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GHSGT-SCIENCE_PHYSICS OF PHYSICAL SCIENCE STUDY GUIDE

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Motion is the change of position in a certain amount of time. The motion of an object can be measured by its speed. Speed is the distance traveled in an unit of time; it is the “rate of motion”. To calculate speed,

Speed = Distance v = d

Time t

Speed can be described in 3 ways:

• Instantaneous – speed at a given instant speedometer • Constant – speed that does not change; moving at a steady pace • Average – opposite of constant speed; total distance divided by the total time

Velocity describes the speed and direction of a moving object.

Sample Problems 1. A car travels 240 km in 3 hours. What is the speed of the car during that time? 2. The speed of a cruise ship is 50 km/hr. How far will the ship travel in 14 hours? 3. Sound travels at a speed of 330 m/sec. If a lightning bolt strikes the ground 1000 m away

from you, how long will it takes for the sound to reach you? A change in velocity in a unit of time is called acceleration. The velocity change may be due to a change in speed, a change in direction, or both. To calculate acceleration, Acceleration = Change in velocity a = Δv

Time t

Change in velocity (Δv) = Final velocity – Initial velocity

Generally, the unit for acceleration is m/sec2.

Positive acceleration a moving object is “speeding up” Negative acceleration (deceleration) a moving object is “slowing down”

Sample Problems

1. A swimmer speeds up from 1.1 m/sec to 1.3 m/sec during the last 20 seconds of the workout. What is the acceleration during that time?

2. A roller coaster is moving at 25 m/sec at the bottom of a hill. Three seconds later, it reaches the top of the next hill, moving at 10 m/sec. What is the acceleration of the rolling coaster?


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Momentum measures how strongly an object tends to keep moving; it asks “how hard it is to stop a moving object?” To calculate momentum,

Momentum = Mass X Velocity p = m X v

The unit for momentum is kg m/sec.Momentum depends on mass and velocity. The more mass and/or more velocity a moving object has, the greater its momentum. Sample Problem: What is the momentum of a 0.30 kg blue jay flying at 17 m/sec?

Law of Conservation of Momentum When a collision occurs, the momentum of one object is transferred to another object. Thus,

Total momentum before collision

= Total momentum after collision

No matter how the two objects collide, the total momentum of the two objects is always the same. Momentum is always conserved. Sample Problems: Two train cars traveling in opposite directions will collide with each other under the following conditions:

Train Car Mass Velocity A 10 kg 14 m/sec east B 10 kg 10 m/sec west

a) What is the momentum of Train Car A? b) What is the momentum of Train Car B? c) What is the total momentum? d) Which train car has more momentum? Explain. e) The two train cars collide and stick together. In which direction do you think both cars will

move?


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A force is a push or pull. It can also do the following: It can start or stop motion It can give energy to an object It can change the direction of a moving object

The unit for force is Newton (N). Vectors

Velocity, acceleration, and momentum are examples of a vector quantity. A vector quantity is anything that has magnitude (size, distance, or amount) and direction. These quantities can be represented by arrows called vectors.

Same magnitude, different directions Different magnitudes, same direction Force is also a vector quantity and can be represented as a vector (or arrow). The length of the vector represents the magnitude of the force, and the direction of the vector indicates the direction of the force.

Combining Forces We can use vectors to show how forces acting on an object can combine. A. Adding forces – Combining forces in same direction If more than one force are acting on an object in the same direction, then the forces are added together. 1 N 2 N 1 N B. Subtracting forces – Combining forces in opposite directions

1. Balanced forces – When two equal forces are acting in opposite directions, the forces cancel out each other.

1 N 1 N 0 N

Thus, with balanced forces, there is no change in motion (i.e., the object is either moving at a constant speed or not moving at all). 2. Unbalanced (Net) forces – When two forces of different magnitudes are acting in

opposite directions, the forces are subtracted. The direction of the resultant force will be the same as that of the larger force.

2 N 3 N 1 N

Thus, an unbalanced (net) force can change the motion of an object.

1 kg mass

1 kg mass

1 kg mass

1 kg mass

1 kg mass

1 kg mass


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Friction is a force opposing motion. It will cause a moving object to slow down and finally stop. It occurs whenever two surfaces are touching each other. The amount of friction depends on how hard the surfaces are forced together and on the materials of which the surfaces are made.

When you exert a force on an object in one direction, friction will always act in the opposite direction. Thus, to overcome friction, a larger force must be exerted. Three types of friction

Static – both objects are stationary Kinetic – both objects are in motion (sliding or rolling) Fluid – force exerted by a liquid or gas (example: air resistance)

Friction can be helpful or harmful. Ways to decrease friction

Lubricate the surfaces with motor oil, wax, grease, etc. Smooth the surfaces Place ball bearing between the surfaces

Newton’s Laws of Motion

1st Law: An object at rest will remain at rest and an object in motion will remain in motion at constant velocity unless acted upon by an unbalanced force; also called the “Law of Inertia”. [NOTE: An object in motion tends to always move in a straight line.]

2nd Law: Force, mass, and acceleration are related.

Force = mass X acceleration F = ma Remember, the unit of force is Newton (N).

1 N = 1 kg X 1 m/sec2 NOTE: The acceleration of an object is directly proportional to the net (or applied) force on the object and inversely proportional to the object’s mass. TRENDS: Comparing two or more objects under the 2nd Law of Motion

1. The larger the mass, the greater the applied force if the accelerations are the same [Ex: one person rolling a 3-kg ball and a 6-kg ball down the street]

2. The larger the mass, the less it accelerates if the applied forces are the same [Ex: pushing an empty shopping cart and pushing a shopping cart full of groceries]

3. The greater the acceleration, the greater the force if the masses are the same [Ex: two identical cars one person pushing one car; two persons pushing the other car]


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Sample Problems 1. A 50-kg skater pushed by a friend accelerates 5 m/sec2. How much force did the friend

apply? 2. A bowling ball rolled with a force of 15 N accelerates at a rate of 3 m/sec2; a second ball

rolled with the same force accelerates at 4 m/sec2. Which ball do you think will have the greater mass? To verify your answer, calculate the mass of each ball.

3. If a 60-kg person on a 15-kg sled is pushed with a force of 300 N, what will be the person’s acceleration?

3rd Law: For every action, there is an equal and opposite reaction; all forces come in pairs. ALL FORCES ACT IN PAIRS!

Some forces can be seen or felt; some forces cannot be seen or felt. Nevertheless, they are present!

Gravity is a natural force of attraction that occurs between two (or more) objects. It exists throughout the universe. Gravity depends on the masses of the objects and the distance between them.

The bigger the object, the more gravitational pull (gravity) it has

The closer the two objects are, the greater the gravitational pull between them

The further the two objects are, the lesser the gravitational pull between them

On Earth, the gravity pulls any falling object (excluding air resistance) toward the center of Earth at the same rate “free-fall”. The acceleration due to gravity (“free-fall”) is 9.8 m/sec2. That means, on Earth, a falling object will accelerate to the ground at 9.8 m/sec2. Of course the free-fall acceleration is different on other planets in the solar system. Some planets have higher/lower gravitational pull than Earth.


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MASS VS. WEIGHT THE FORCE OF GRAVITY Mass is the amount of matter an object has; weight is the amount of gravitational pull exerted on an object. Since weight depends on gravity, it can change. Mass doesn’t ever change; it is always constant. Since weight is a force (SI Unit: Newton), we can calculate it as follows:

Sample Problems An astronaut has a mass of 66 kg.

a). Calculate his weight (in Newtons) on Earth. b). Calculate his weight on the moon (gravity is 1.6 m/sec2). c). Why did the weight of the astronaut change when he went to the moon? d) Did his mass change? Why or why not?

Work has a common, everyday meaning, but it also has a scientific meaning. Work measures the effects of force acting over a distance. The unit for work is called Joule (J) Work is only done when force cause a change in the motion of an object. Power measures the rate at which work is done. That is, how much work is done in a certain amount of time? The unit for power is called Watt (W)

Sample Problems 1. A father was playing with his daughter by lifting her repeatedly in the air. How much work

does he do with each lift, assuming he lifts her 2.0 m and exerts an average force of 190 N? 2. It takes 100,000 J of work to lift an elevator 18 m. If this is done in 20 seconds, what is the

power of the elevator during the process?

Weight = mass x gravity

W = mg

where the acceleration of gravity on Earth is 9.8 m/sec2.

Work = force x distance W = F x d

1 J = 1 N x 1 m

Power = Work/time P = W/t

1 W = 1 J/1 sec


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A machine is a device that makes work easier; it can change the size or the direction of the force you exert. WITH OR WITHOUT A MACHINE, THE AMOUNT OF WORK DONE WILL BE THE SAME! There are six types of simple (basic) machines. They are divided into two groups:

The Lever Family The Inclined Plane Family Simple lever Inclined plane Pulley Wedge Wheel and axle Screw

Simple Machine How does it make work

easier? Examples

A simple lever is a straight, rigid bar that rest on a support called a fulcrum

Lifts or moves things Shovel, nutcracker, screwdriver, broom, crowbar, bottle opener, seesaw, forearm, jack (car)

A pulley is a grooved wheel with a rope or cable around it; it’s a modified lever

Moves things up, down, and across

Curtain rod, tow truck, mini-blind, flag pole, crane

A wheel and an axle is a wheel with a rod (called an axle) through its center; both parts move together. It’s a turning lever.

Moves things; lifts things Cars (steering wheels and tires on the car), wagons, bicycles, doorknob, pencil sharpener, skateboard

An inclined plane is a slanted surface connecting a lower level to a higher level

Moves things up or down on it Slide, stairs, ramp, escalators, slope

A wedge is made from two inclined planes placed back to back; it has at least one slanted side and a sharp edge

Cuts or spread an object apart Knife, pin, nail, chisel, ax, snowplow, front of a boat

A screw is an inclined plane wrapped around a cylinder or a pole

Holds things together or lifts things

Screws, jar lids, bottle caps, bottom of a light bulb, corkscrew

A compound machine is made of two or more simple machines. The mechanical advantage (MA) of a machine tells us how much a machine multiplies force or distance; it describes how easier the machines get the work done. The larger the MA, the less effort needed to get the work done. There are two types of MA – Ideal and Actual. A. Ideal Mechanical Advantage (IMA)

• It is the MA of an ideal machine (the “perfect” machine which is frictionless) • It is theoretical – “that’s what it is supposed to be” • To calculate IMA, IMA = Effort distance

Resistance distance


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B. Actual Mechanical Advantage (AMA) • It is the MA of a real machine • It takes into consideration real world factors (i.e., friction and energy lost) • To calculate AMA,

Where,

• Effort force/distance – the force/distance applied by you to move an object • Resistance force/distance – force/distance applied by the machine to overcome

resistance (weight of object being moved) In this class and on future tests, unless otherwise it is stated that the machine is ideal, ALWAYS ASSUME WE ARE DEALING WITH REAL MACHINES (SOLVE FOR AMA – even if friction is ignored)! For inclined planes,

Length

Height For simple levers,

Resistance force (load) Effort force Fulcrum Where the effort force is the force YOU exert on the lever and the resistance force is the force exerted on the object (can be the object’s weight) For wheels and axles,

Wheel Axle

MA = length/height

MA = distance of the effort force from the fulcrum distance of the resistance force from the fulcrum

MA = radius of the wheel/radius of the axle

AMA = Resistance force Effort force


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For pulleys, Resistance force (load) Effort force The efficiency of a machine compares the work output to the work input The amount of work done by the effort force is the work input. The amount of work done on the resistance (load) is the work output. In the real world, because extra work must be done to overcome friction, work input is always greater than work output. Since extra work must be put into the machine to overcome friction, work output can never be greater than work input. The efficiency of a machine can never be greater than 100 %; in fact, there is no machine that is 100 % efficient since friction is always present. Sample Problem: Jordan used a crowbar to open a crate. She applied a force of 10 N to the end of a 30 cm (0.3 m) crowbar. The resistance of the crate lid was 40 N, and it opened 6 cm (0.06 m). [Assume friction is ignored]

a) What is the mechanical advantage? b) What was the efficiency of the crowbar?

MA = # of rope segments pulling on the resistance force (load)

Efficiency = Work Output x 100 % Work Input


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Energy – the ability to do work; SI Unit for energy is Joules (J)

Two States of Energy Kinetic energy (KE) – energy of motion

Any moving object has kinetic energy

KE depends on mass and velocity The more mass and/or velocity a moving object has, the greater its KE To calculate KE,

KE = ½ mv2 Where, • m = mass (kg) • v = velocity/speed (m/s)

Potential energy (PE) – energy of position; stored energy An object with PE has the potential, or the ability, to

do work or release energy PE stored in a spring, bungee cord, or rubber

band is called elastic PE PE from the height off the ground is called

gravitational PE – the higher the object is off the ground, the greater its gravitational PE

To calculate gravitational PE, PE = mgh

Where • m = mass (kg) • g = acceleration due to gravity (9.8 m/s2) • h = height from the ground (m)

Sample Problems

1. A 65-kg rock climber ascends a cliff. What is the climber’s gravitational PE at 35 m above the base of the cliff?

2. What is the KE of a 44-kg cheetah running at 31 m/s?

Five Main Forms of Energy Main Form of Energy Description State of

Energy Examples

1. Mechanical energy involves energy from matter that is in motion

KE water in a waterfall, wind, sound, any moving object, any physical activity

2. Heat energy involves energy from the internal motion of atoms/molecules the faster the particles move, the more heat energy is produced

KE any temperature change, phase changes (i.e., melting, freezing, etc.)

3. Chemical energy involves energy from forming or breaking bonds between atoms

PE jet fuel, gasoline, food, batteries (all have stored energy)

4. Electromagnetic energy

involves energy from moving electric charges

KE electricity, light, X-rays, radio/TV waves, laser light


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5. Nuclear energy involves energy from the nucleus (center) of an atom

PE

nuclear fission (splitting of nuclei) and nuclear fusion (joining of nuclei powers the sun and other stars)

The Law of Conservation of Energy states that energy cannot be created or destroyed by ordinary means; however, it can change from one form to another. Changes in the form of energy are called energy conversions (or energy transformations.) One of the most common energy conversions is KE PE or PE KE.

Dropping an book from a table Riding a roller coaster A pendulum in motion Tossing a ball in the air

All forms of energy can be changed to other forms.

Solar powered products (e.g., solar cells) Sunlight electricity

Electric motors Electricity mechanical energy (movement, sound, etc.)

Robot Battery electricity mechanical energy (movement, sound, etc.)

Photosynthesis Sunlight Sugars & starches in green plants (chemical)

Electricity from power plant Fuel such as coal (chemical energy)/nuclear fission (nuclear energy) Heated water steam (heat energy) Steam turns turbines in generators (mechanical energy) Generator produced electricity (electromagnetic energy) Electricity traveled to homes and businesses

Temperature is a measure of the average kinetic energy of all the particles within an object; they are measured using an instrument called a thermometer. [REMEMBER – KE depends on mass and velocity. Therefore, the bigger the particles and/or the faster the particles are moving, the more KE they possess and the greater the temperature.]


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Temperature Conversions There are three temperature scales:

a) Fahrenheit (oF) – used in weather reports and in cooking b) Celsius (oC) – commonly used scale in science

c) Kelvin (K) – SI unit for temperature

The Kelvin temperature scale contains the lowest/coldest possible temperature – absolute zero (0 K). At absolute zero, the particles of an object have NO KINETIC ENERGY – THE PARTICLES ARE NOT MOVING! Also, unlike the oC and oF scales, the Kelvin scale has NO NEGATIVE TEMPERATURES.

Sample Problems 1. Water boils at 100 oC. Express this temperature in oF and K. 2. What is the temperature of absolute zero in oC and oF? 3. The freezing point of water is 32 oF. Convert this temperature to oC and K. Heat is the transfer of energy from an object with a high temperature to an object with a lower temperature.

Three methods of heat transfer 1. Radiation – transfer of heat by rays or waves sun energy reaches Earth this way 2. Conduction – transfer of heat when molecules collide into each other through direct

contact 3. Convection – transfer of heat by the circular flow of a fluid (liquid or gas) due to density

difference Density describes how light or heavy an object is. Cold air is heavier (more dense) than warm air because the air molecules are closer together in cooler air. Thus, cold air sinks as warm air rises. When cold air forces warm air to rise, a circular movement of air, called convection current, occurs. Similar action will occur with liquids.

------------------------------------ Metals are good conductors, because they can easily carry heat energy. Wood, rubber, and Styrofoam are insulators, because they are poor conductor of heat. A physical property, specific heat is the amount of heat energy that will raise the temperature of 1 kg of a substance by 1 K; it describes how much energy is required to raise an object’s temperature. Some materials can take in more heat than others.

oF = (9/5 x oC) + 32

oC = 5/9(oF – 32)

K = oC + 273 or oC = K – 273

Heat Energy (HE) = cmΔt

Where c = specific heat (J/kg K) m = mass of substance (kg) Δt = temperature change = tf – ti (in Kelvin)


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Sample Problems 1. How much heat energy must be transferred to the 420 kg of water in a bathtub in order to

raise the water’s temperature from 25 oC to 37 oC? The specific heat of water at 25 oC is 4186 J/kg K.

2. What is the specific heat of aluminum with a mass of 0.455 kg that has absorbed 6330 J of heat energy, thus having a temperature change of 15.5 oC?

Phase Changes – Changes of State of Matter

Absorb Heat Energy Melting Solid Liquid

Evaporation Liquid Gas *Sublimation Solid Gas

Release Heat Energy Condensation Gas Liquid

Freezing Liquid Solid An energy change is always the cause for a phase change. A phase diagram shows the relationship between temperature and heat energy during a phase change.

Temperature

Gas Liquid Solid

Heat energy

During a phase change, the temperature remains unchanged; however, heat energy is absorbed or released.

• Melting point – the temperature of a substance changing from a solid to a liquid • Freezing point – the temperature of a substance changing from a liquid to a solid

Note – On the phase diagram, the melting point and the freezing point are the same temperature • Boiling point – the temperature of a substance changing from a liquid to a gas • Dew (condensation) point – the temperature of a substance changing from a gas to a

liquid Note – On the phase diagram, the boiling point and the dew point are the same temperature


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What are waves? Moving disturbances/vibrations that transfers energy (not matter) from one place to

another Medium – matter that a wave travels through Most waves are mechanical waves (they travels through a medium); electromagnetic

waves do not travel through a medium Most waves are periodic; they have a repeating pattern of motion

Two Classes of Waves

Transverse Waves These waves moves perpendicular (up-and-down motion) to the direction of the wave Water waves and light are examples

Longitudinal (or Compression) Waves These waves moves parallel (back and forth) to the direction of the wave The “slinky” and sound waves are examples

Characteristics of Waves A. Transverse Waves

Crest – the highest point of a wave Trough – the lowest point of a wave Amplitude – distance of the wave from rest Wavelength – the distance from one point of the wave to the same point of the next wave Period (T in sec) – the time it takes a wave to pass by a certain point Frequency – the number of waves that pass a point in one second [unit of frequency =

Hertz (Hz) = 1/sec] NOTE – Frequency = 1/T (period)


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B. Longitudinal/Compression Waves Compression – areas in medium where particles are squeezed together Rarefaction – areas in medium where particles are spread apart Wavelength – distance from one compression to the next Amplitude – half the distance between compressions Frequency – the number of waves per second

||||||||||||| | | | | | ||||||||||||||| | | | | | ||||||||||||||| | | | | | |||||||||||||||| | | | | |||||||||||||||| | | | | | |||||||||||||||| To calculate the speed of a wave,

Wave Speed (ν) = wavelength (λ) x frequency (f) ν = λf

The amplitude of a wave depends on its energy; the larger the amplitude, the greater the energy.

The frequency of wave depends on its speed; the faster the wave is moving, the greater its frequency. Wavelength and frequency are inversely proportional; waves with shorter wavelengths have higher frequencies (and vice versa).

The speed of a wave depends on the type of medium it passes through.

Sample Problems 1. What is the speed of a wave that has a wavelength of 1 m and a frequency of 2 Hz? 2. Sound waves travel through air at 343 m/sec. Suppose a sound wave has a frequency of 1000

Hz. What is its wavelength?


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Waves travel in straight lines until they hit a boundary. When this occurs, one of three things can happen; the wave will be reflected, refracted, or diffracted. A. Reflection – the bouncing back

of a wave when it hits a boundary

B. Refraction – the bending of a wave as its changes speed by moving through a different medium

C. Diffraction – the scattering of a wave as its hits the edges of a boundary or tiny opening

When two or more waves are moving through a medium at the same time, the energy of the waves may interact by adding together or canceling out as they pass. This is called interference.

Waves in same medium Description Combined waves Constructive interference

• Crest-crest overlapping

• Add the amplitudes • Form bigger wave

Destructive interference • Crest-trough

overlapping • Subtract the

amplitudes • Form smaller wave

(different sizes) • Form straight line

(same size)


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General Characteristics of Sound Waves Sound waves are longitudinal/compression waves

They transfer sound, which is a form of energy, from one place to another The sound we hear are produced by vibrations of the longitudinal/compression waves Sound waves are mechanical waves – needs a medium

Speed of Sound Waves

The speed of sound waves depends on the medium which the waves travels and its temperature

The closer the particles are in a medium, the greater the speed of sound wave; sound waves transmit energy faster in substance with smaller spaces between particles more vibrations

solid (more dense) liquid gas (less dense)

speed of sound increase

Air is the most common medium of sound waves The higher the temperature of the medium, the more particles of the medium will

collide (causing vibrations). Therefore, more energy can be transmitted in a shorter amount of time increase the speed of sound.

Sound cannot travel in a vacuum (area where there is no air particles)

Speed of Sound through Various Substances Air (at 0 oC) 331 m/sec Wood 3828 m/sec Air (at 25 oC) 346 m/sec Iron 5103 m/sec Water (at 25 oC) 1454 m/sec Stone 5971 m/sec

1. Which of the above items would you believe to be the most dense? Why? 2. What would happen if you increased the temperature of these items?

The speed of sound is much slower than the speed of light (3.0 x 108 m/sec). Light waves travel through air about one million times faster than sound waves. This is why you see lightning before hearing the sound (thunder).

Properties of Sound

1. Volume/Intensity – the softness or loudness of sound depends on the amplitude of the sound wave

a. The greater the amplitude, the greater the volume/intensity (the louder the sound) the more energy a wave has

||||||||||| | | | | ||||||||||| | | | | |||||||||| | | | | |||||||||| | | | | direction of wave


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b. SI Unit of volume/intensity – decibels (dB)

10 – 20 dB very faint Whisper, human breathing, rustle of

leaves 20 – 40 dB faint Quiet home, quite conversation, private

office 40 – 60 dB moderate Noisy home, movie theater, loud

conversation 60 – 80 dB loud Noisy office, loud radio, opera singers

singing 80 – 100 dB very loud Noisy machine shop, rock/rap concert,

truck unmuffled 100 – 120 dB results in hearing loss Jet in flight, firing range, explosion

c. Continual/prolonged exposure to sound with an intensity greater than 90 dB can cause permanent hearing damage/loss

2. Pitch – the highness or lowness of sound depends on the frequency of the wave a. The higher the frequency, the higher the pitch

b. The human ear can hear sound frequencies from 20 Hz to 20,000 Hz c. Sound waves are described as infrasonic (frequencies less than 20 Hz) or

ultrasonic (frequencies greater than 20,000 Hz) most humans cannot hear either of them

3. Timbre/Sound Quality – the blending of different-frequency sound waves If the source of the sound wave is moving, like a train blowing the whistle while moving down the tracks or an ambulance blasting its siren while moving along a street, a phenomenon called the Doppler effect occurred.

As the source moving toward the observer, the frequency of the sound wave appears higher louder. The sound waves are closer together in front of the source.

As the source moves away, the frequency of the sound wave appears lower softer. The sound waves are farther apart behind the source.

Thus, the Doppler effect is the change in wave frequency (pitch) caused by the motion of the wave source.


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In physics, the study of sound is called acoustics. Irregular or unpleasant sounds are called noise. Too much “noise” may cause health and/or hearing problems. Sounds having a pleasing quality and a regular pattern are called music.

The reflection of a sound wave is called an echo. If you hear multiple echoes of sounds, you will experience reverberation – making it difficult to hear clearly. The sounds reflecting off different things in the room reach your ears at different times. In many auditoriums, theaters, and concert halls, soundproofing materials (i.e., carpets and long curtains) are placed on walls to reduce reverberation by absorbing sound and eliminating echoes. Although human cannot hear them, echoes of ultrasonic waves are useful in many ways.

1. Oceanography – SONAR (acronym for SOund NAvigation and Ranging) use to find the depth of water or sunken ships.

2. Medicine (called Ultrasound) – use to remove kidney stones and “see” the inside of the body (locate tumors/gallstones or examine a developing fetus inside their mothers). The reflected waves are fed into a computer, which provides a picture called a sonogram.

3. Use in cleaning jewelry, machine parts, and electronic components. Items are placed in a bath of water, and ultrasonic waves are sent creating strong vibrations in the water the remove dirt from items in bath.

Electromagnetic (EM) Waves

• All EM waves are transverse waves; they moves perpendicular (up and down) to the direction of the wave

• They can travel in a medium or in a vacuum (empty space with no air particles) – do not require a medium!

• All EM waves are formed by the motion of electrically charged particles • All EM waves travel at the same speed in a vacuum: 3 x 108 m/sec (the speed of

light). They travel slower in a medium – still faster than the speed of sound. • EM waves, however, are classified by their wavelengths and frequencies SEVEN

TYPES OF EM WAVES Longest Radio waves Lowest

Wavelength

Microwaves Frequency (& Energy)

Infrared (heat) waves

Visible light

Ultraviolet (UV) waves

X-rays

Shortest Gamma rays Highest

Visible Light and “Seeing” Colors

• The only EM waves the human eye can SEE • ROY G BIV – the order of colors increasing frequencies and decreasing

wavelengths o Red – longest wavelength & lowest frequency o Violet – shortest wavelength & highest frequency


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• White light is a mixture of many colors. These colors can be separate when white light is refracted (bended) in a prism.

• Seeing colors

o We can see color because our eyes see each wavelength as a different color

o When white light strikes most objects, certain colors are reflected (bounced off) while others are absorbed

o The REFLECTED LIGHT is what you see as color o [Example] A BLUE object appears blue because it reflects mostly

wavelengths of blue light; all other colors are absorbed by the object o When all wavelengths/colors are reflected, the object appears white; when

all wavelengths/colors are absorbed, the object appears black o The human eye can see about 17,000 different colors

Light can be refracted (bended) when it can pass through a different medium.

It can also be refracted when it passes through lens. Light bends toward the thicker part of the lens.

In convex lens, the light rays converges, or come together, at a focal point

In concave lens, the light rays diverges, or spread apart


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TYPES OF

WAVES RANGE OF

FREQUENCYRANGE OF

WAVELENGTHUSAGES

RADIO WAVES

Less than 1 x 109 Hz

Greater than 30 cm

AM and FM radio; television broadcasting; radar; air craft navigation; MRI in medicine; radio telescopes

MICROWAVES

1 x 109 – 3 x 1011 Hz

30 cm – 1mm Microwave cooking; telecommunication; research on atoms and molecules

INFRARED (HEAT) WAVES*

3 x 1011 – 4.3 x 1014 Hz

1 mm – 700 nm Heat radiation from sun; heating lamps for warming foods; hair-dryer; heat-sensitive or “night vision” cameras and weapons

VISIBLE LIGHT

4.3 x 1014 – 7.5 x 1014 Hz

700 nm – 400 nm

Visible light photography; optical microscopes and telescopes

ULTRAVIOLET (UV) LIGHT*

7.5 x 1014 – 5 x 1015 Hz

400 nm – 60 nm Sterilizing medical instruments; killing harmful bacteria in foods; identifying fluorescent minerals

X-RAYS*

5 x 1015 – 3 x 1021 Hz

60 nm – 1 x 10-4 nm

Medical examination of bones, teeth, and organs; detected for black holes in space

GAMMA RAYS*

3 x 1018 – 3 x 1022 Hz

0.1 nm – 1 x 10-5 nm

Cancer treatment; food irradiation; energy used in nuclear power plants to create electricity

* Prolonged/excessive exposure to these types of waves can cause serious health problems, genetic mutation, and even death

WAVELENGTH LONGER SHORTER

RADIO WAVES

MICROWAVES

INFRARED (HEAT) WAVES

VISIBLE LIGHT

ULTRAVIOLET (UV) LIGHT

X-RAYS

GAMMA RAYS

R O Y G B I V

LOWER HIGHER

FREQUENCY AND ENERGY

RED ORANGE YELLOW GREEN BLUE INDIGO VIOLET

700 nm 400 nm WAVELENGTH (λ)


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Electricity is also called electrical energy. It is energy due to the movement of electrically charged particles.

Two Types of Electricity A. Static electricity – the accumulation (build-up) of electrically charged particles on an

object DOES NOT FLOW a. Take a comb and rub it through your hair; afterwards, use the comb to pick up

small pieces of paper b. Rub a balloon in your hair and watch as it stick to the wall c. Walk across a carpeted floor and be stung by a spark when you reach out to touch

something d. Place clothes in dryer and see how they “cling” to each other

B. Current electricity – the flow of electrically charged particles through a wire or a conductor (material that can carry electricity through it)

With any type of electricity, it all begins with the atom. In an atom, there are three subatomic particles:

Particle Charge Location Movement in Atom

Proton +1 Nucleus None Neutron 0 (neutral) Nucleus None Electron -1 Electron cloud Constantly in motion An atom is electrically neutral if it has the same number of protons and electrons. However, in some atoms, electrons are not held tightly. As a result, those atoms lose electrons thus, becoming positively charged. Whereas, in other atoms, they attract additional electrons thus, gain electrons and becoming negatively charged.

Static Electricity Law of Electric Charge: Electrically charged objects obey the following rule: Opposite charges attract, and like charges repel!

Static electricity can occur in three ways: By friction

• As two electrically neutral objects are rubbed together, one object will lose electrons to the other object.

• The object that lost electrons becomes positively charged and the object that gains electrons becomes negatively charged.


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By conduction • When a negatively charged object and a positively charged object are brought

together, the effects of both charges are cancelled out. • Electrons will move from one (-) object to the other (+) object until both objects are

neutral. By induction

• A charged object is brought near a neutral object • The opposite charge will be attracted toward the charged object

forcing the neutral object to behave as if it was charged

If the charges are strong enough, the objects do not even need to touch for this exchange to take place. Electrons can jump a gap between two oppositely charged objects. When this happens, the charge heats the air enough to make a spark. After the spark (transfer of electrons), both objects are electrically neutral. This process of transferring electric charges is called electric discharge. Static electricity may be discharged if a charged object comes in contact with an object that will accept the charge. Lightning is a spectacular example of electric discharge.

Current Electricity

The amount of electric current (flow of electrons) depends on the number of electrons passing a point in a given time. The coulomb (C) is the unit of electrical charge. It takes 6.25 x 1018 electrons to make a charge of -1 coulomb (or 6.25 x 1018 protons to make +1 coulomb). There are two types of current:

Direct Current (DC) o Current that move in ONE direction o Produced by battery (changes chemical energy into electricity)

Alternating Current (AC) o Current repeatedly changing direction (ALTERNATING direction) travel

longer distances o Produced by generator (changes mechanical energy into electricity)

Three Basic Units of Electricity

A. Current (I) – flow of electrons [SI Unit – Ampere (Amps or A) = Coulomb/second] B. Voltage (V) – the work/energy that push electrons from one point to another [SI Unit – Volts

= Joule/coulomb]; also called potential difference C. Resistance (R) – measures how much a substance opposes the flow of electrons, or current.

(SI Unit – Ohms or Ω); also called electric friction


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Ohm’s Law describes the relationship of the three basic units of electricity.

Sample Problems:

1. What is the resistance of a circuit if the current is 4 amps and the voltage is 12 volts? 2. What voltage is needed to cause a current of 3 amps to flow through a 2 ohm resistor? A circuit is a closed path through which electricity can flow. Every circuit must have these 4 components:

1. A source of electricity – battery (or generator) a. Will have a positive terminal and a negative terminal b. Electrons will be “pushed” from the negative terminal at a certain voltage c. Through a wire, the electrons will flow to the positive terminal

2. A switch a. Controls the flow of electric current b. Made of a conductor attached to an insulator (material that cannot carry electricity

through it) c. When the switch is closed, the current can continue to flow though the entire

circuit; If the switch is opened, NO current can flow 3. One or more loads

a. Provide resistance b. Convert electricity into other forms of energy, like heat, light or sound c. Light bulb, toaster, motor, TV, etc. (any electrical device)

4. Wires (at least two) a. Consist of copper or aluminum (conductor) surrounded by rubber (insulator) b. Carry electricity between the source and the load(s) c. Electrons move from the source (- terminal) to the load(s) and back to the source

(+ terminal)

Symbols of Parts of an Electric Circuit

Battery - +

Switch

open

closed Load

any electrical device – zigzag

a light bulb Wires

or single connected

Voltage = Current x Resistance V = IR


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Two Types of Circuits Series Circuit – only ONE path for the current to follow

A break anywhere along the path will stop the current flow Parallel Circuit – has more than one path for the current to flow

A break along one path will NOT stop the current flow in the other paths Then there are some circuits that are a combination of series and parallel circuits.


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Magnetism is a force produced by the motion of charged particles.

A magnetic field is an area around a magnet where the magnetic force is observed. These lines are a way to show the structure of a magnetic field. The lines are close together where the magnetic force is strong, and spread out where it is weak; thus the magnetic force is greatest at the north and south poles. Also, the line (or “force”) always travels from the north pole of the magnet to the south pole.

Within a magnet, a group of atoms, called domains, have electrons spinning in the same directions creating a magnetic field in the material

• Domains lined up in an orderly fashioned magnetized • Domains in disarray not magnetized

Every magnet is a dipole; it has two poles – north and south poles. Even if you break a magnet in half, the two pieces will have their own dipoles.

In fact, our Earth is one large magnet, with its two poles. The north pole of a magnet is attracted to the magnetic North Pole of the Earth; this explains why, in a compass, the needle always points north.


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Think of the Earth as a gigantic bar magnet buried inside. In order of the compass needle to always point to the North Pole, we have to assume that the buried bar magnet has its south end at the North Pole.

Law of Magnetism states this:

• Like magnetic poles repels • Unlike magnetic poles attracts

Thus,

N S

N S N S

N S S N


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Like any magnet, our Earth has a magnetic field of its own magnetosphere.

• It protects us from solar wind (a stream of charged particles blown from the sun which can be harmful to humans)

• It creates beautiful auroras (northern/southern lights) around the poles, due to charged particles from solar wind that are trapped in the Earth’s magnetic field

There are two types of magnets – permanent and temporary.

A. Permanent magnets are substances that are “magnetic” all the time. The most common permanent magnet is lodestone (or magnetite), a rock mostly made of iron.

B. A temporary magnet (also called an electromagnet) is a device that becomes “magnetic” when its magnetic field is produced by an electric current.

A simple electromagnet consists of a copper wire wrapped

around an iron nail attached to a battery. To increase its magnetic strength,

a. Add more coils* (“loops”) around the nail b. Use iron nails only – no other metal c. Increase current use larger batteries d. Decrease the distance of the coiled iron nail and the

battery

When electricity runs through the wire, it produces a magnetic field in a specific direction. Use the “right hand rule” to determine the direction of the magnetic field. • Your thumb points in the direction of the electric

current • Your fingers point in the direction of the magnetic field

around the wire

*A coil of wire – not wrapped around a nail – used to create a magnetic field is called a solenoid Just as an electric current can produce a magnetic field around a wire, a magnetic field can also produced an electric current in a coil of wire. As the coil moves through a magnetic field, it produces electricity by inducing a voltage from the coil of wire. This is how a generator works.


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A generator is a machine that changes mechanical energy into (AC) electricity. Below is a diagram of a simple generator.

NOTE: In the diagram, the coil is stationary and the magnet – providing the magnetic field – is moving. You can have a coil of wire moving through or around a stationary magnet found in generators at power plants. The electricity produced by generators can have its voltage regulated by the use of a transformer. A typical transformer (shown below) consists of a large iron ring with two coils – primary and secondary – wrapped around it. AC current flows through the primary coil, producing a magnetic field in the iron ring that will induce a current in the secondary coil.

We use transformers to change the size of the voltage; we can step the voltage down from a high voltage to a smaller one or we can step it up.

A. Step-Up Transformers a. Secondary coil has more loops than the primary coil b. Outgoing current has higher voltage c. Used at power plants to transport electricity over longer distances

B. Step-Down Transformers a. Secondary coil has fewer loops than the primary coil b. Outgoing current has lower voltage c. Placed near homes to reduce voltage to safer levels


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To calculate the outgoing voltage, Sample Problem: The primary coil of a transformer contains 20 turns of copper wire. In the secondary coil, there are 100 turns of wire. If the voltage going into the transformer is 12 V, what is the outgoing voltage? What type of transformer is this? While generators used motion to create electricity, electric motors used electricity to create motion. Thus, an electric motor is a device that changes electricity into mechanical energy. In a simple electric motor (shown below), an electromagnet rotates around (or within) a permanent magnet; this rotation is due to the magnetic fields alternatively attract and repel each other.

You know magnets can be used to produced electricity (and vice versa)

Did you know? Magnets are used in

• Refrigerators, vacuum cleaners, washing machines, CD and DVD players, blenders, hedge trimmers any household device that used a motor

• Cars, trains, subways (yes…including MARTA) • Maglev trains – use repelling forces of magnets to cause the train to levitate (float

above the track); because it levitate, it eliminates friction so these trains can travel at high speeds

• Computers information is saved and retrieve • Audio and video players used magnetic “heads” to record and read information on

tape covered with tiny magnetic particles • Speakers and microphones • Images on TV screen • Escalators and elevators • Magnetic Resonance Imaging (MRI) – patient lies between two large magnets,

causing the domains in the human body to align; use to view inside the body

Voltage out = Turns in secondary coil Voltage in Turns in primary coil

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