Objective 1: Relate the Conservation of Energy to energy transformations

Describe how energy--mechanical, electrical, chemical, light, sound, and heat--can be transformed from one form to another

Show understanding that energy transformations result in no net gain or loss of energy, but that in energy conversions less energy is available due to heat loss.

Apply Conservation of Energy

Apply the concept of conservation and transformation of energy within and between organisms and the environment--such as food chains, food webs, and energy pyramids

Apply the concept of conservation and transformation of energy to other everyday phenomena.

Objective 2: Relate waves to the transfer of energy

Relate wavelength to energyRelate frequency to energyRelate wavelength to frequencyDescribe how waves travel through

different kinds of media Mechanical waves

Water, Sound, Slinky, etc.

Electromagnetic waves

Describe how waves can be destructive &/or beneficial

Describe how waves--earthquake waves, water waves, and electromagnetic waves--can be destructive (harmful) or beneficial (good) due to the transfer of energy

Destruction (cons)Benefits (pros)

ALL WAVES

Transfer energy from one place to anotherEnergy transferred does NOT have mass.Actual particles of the wave (such as water

waves) are NOT transferred, but stay in the same place

Have wavelength, frequency, amplitudeSHORTER WAVELENGTH means HIGHER

FREQUENCY AND ENERGY!

Mechanical vs. Electromagnetic

Require a medium, or something to travel through (cannot travel through space)

Water waves, waves in a rope or slinky, and sound waves are examples

Require NO medium, can travel through outer space!

Examples of ELECTROMAGNETIC WAVES:

Electromagnetic waves, from low to high frequency:

RADIO WAVESMICROWAVESINFRARED

(HEAT)VISIBLE LIGHTULTRAVIOLETX-RAYS, GAMMA RAYS

LONG wavelength, LOW frequency AND energy

HIGH wavelength, HIGH frequency AND energy

VISIBLE LIGHTOnly a SMALL band of the EM spectrumRegular “white” light can be separated into

all the different colors with a prismThis was discovered by Isaac Newton!RED (longest wavelength, lowest energy)

to VIOLET (shortest wavelength, highest energy)

ROY G BIV stands for Red, Orange, Yellow, Green, Blue, Indigo, Violet

Longitudinal vs. TransverseCompression waves

where one part of a medium smashes into another

Wave particles travel parallel to the energy

SOUND WAVES are longitudinal. They cannot travel in space because there is no medium

Up and down waves, like wiggling a rope back and forth

Wave particles travel perpendicular (at right angles) to the energy being transferred

Electromagnetic waves are transverse!

Electromagnetic vs Sound

ALL travel at the “speed of light”, 186,000 miles/second or 300,000,000 m/s

TransverseDon’t need a mediumCan travel through

outer space, all across the universe

Travels MANY MANY times slower, only about 370 m/s (almost a million times slower!)

LongitudinalRequire a mediumCannot travel through

outer spaceEnergy gets

dispersed(spreads out) quickly

ENERGY

The ability to “do work” or make a CHANGE in something

Energy has many forms, and all can be transformed from one to another

There is a CONSTANT amount of energy in any given closed system, even in the universe as a whole!

ENERGY AND WORKAn “ideal system” means NO friction, and

no energy “lost” as heatEnergy is NEVER destroyed. It is only

“lost” if it becomes unusableIn an ideal system (or machine), you get

ALL the energy OUT that you had to put IN. This is called 100% efficiency.

There are NO “ideal systems” in real life!In REAL LIFE some energy is ALWAYS

changed to “lost” heat because of friction!

ENERGY AND WORK UNITS

MASS is measured in kilograms [kg]WEIGHT and other FORCES are

measured in NEWTONS [N]ENERGY is usually measured in Joules [J]WORK is usually measured in Newton-

meters [N m]SINCE ENERGY AND WORK ARE EQUAL,

A JOULE IS EQUAL TO A NEWTON-METER!

POTENTIAL ENERGY

This is STORED ENERGYMost commonly means

GRAVITATIONAL potential energy, or energy stored because of a position HIGHER than some reference point (like the ground)

Potential energy continued

Can be ELASTIC OR SPRING potential energy, like the energy stored in a stretched rubber band, the spring in a wind up toy, or a drawn bow before shooting an arrow

Potential energy is also stored in batteries, as CHEMICAL potential energy!

POTENTIAL ENERGY continued

POTENTIAL ENERGY can also be stored up in chemical bonds, such as in food or fat

There is a tremendous amount of potential energy in MASS ITSELF, as Einstein showed with E = mc2

MASS itself is like VERY concentrated, congealed energy!

Gravitational potential energy is described by PE = mgh or mass x gravity x height

KINETIC ENERGYEnergy of motion (kine- means MOTION, like

cinema means moving picture or movie!)KE = 1/2 mass times velocity squaredIf something is NOT MOVING, is has ZERO

KINETIC ENERGY!In an “ideal system,” ALL (or 100%) of the

WORK you put IN can be changed to KEIn real machines, most energy is changed

to heat. A car is only about 30% efficient! Only 30% of the gas gets changed to KE!

POTENTIAL energy example

If a rock has a mass of 5 kg, and it is on a hill 2 m high, how much PE does it have?

PE = mgh [or mass in kg x height in meters]g = 10 m/s/sWeight in Newtons = mass in kg x gravity!PE = weight in Newtons x height in meters so PE = 5 kg (10 m/s/s) (2m) = 100 Joules or

100 J !

PE Problems

1. If a rock has 5 kg of mass and is lifted up a 1 m hill, how much PE does it have?

2. If a rock has has 20 N of weight and sits on top of a 2 meter tall box, how much potential energy does it have?

PE Solutions1. PE = mghso PE = 5 kg x 10 m/s/s x 1 m = 50 J

2. PE = weight x heightso PE = 20 N x 2 meters =40 J

Reminder: Weight = mass x gravity. For example, 2 kg of mass X 10 m/s/s = 20 N!

Kinetic energy example

KE = 1/2 mass x velocity squaredIf a 3,000 kg car is traveling at 10

m/s, how much KE does it have?

KE = 1/2 (3,000 kg) (10 m/s)2

= 1,500 (100) = 150,000 J!

Kinetic energy problems

1. If a 60 kg girl is running at 5 m/s, how much Kinetic energy does she have?

2. If the girl stops and sits on a bench to rest, how much kinetic energy does she have?

Kinetic energy solutions1. KE = 1/2 mv2

so KE = 1/2 (60 kg) (5 m/s)2so KE = 30 (25) = 750 J

2. KE = 1/2 (60 kg) (0 m/s)2

so KE = 0 She is not moving, so she has no

Kinetic energy while sitting on the bench!

Potential and Kinetic, transferred back and forth

If you do 20 J of WORK lifting a rock onto a table, how much PE does the rock have?

If the rock then falls off the table, how much KINETIC ENERGY does it have just before it hits the floor?

WHERE did the rock GET the kinetic energy?

When the rock smashes into the floor, where does the energy go?

KE if you double mass

If you had instead lifted a rock with TWICE as much mass, how much more WORK would you have put in to lift it?

How much more PE would it have had at the top?

How much more KE at the bottom?

If you lifted more distance

If, instead of lifting a rock with twice the mass, you lifted the SAME rock twice the height, how much more WORK would you have done?

What if you lifted a rock with TWICE the MASS a distance TWICE AS FAR? How much more Work would you have to do?

Roller Coaster

ON a roller coaster, at what point is your POTENTIAL ENERGY greatest?

Where is your KINETIC ENERGY greatest?

Ignoring energy “lost” as heat due to friction, what can you say about the TOTAL amount of energy for the whole ride on the roller coaster?

Roller Coaster continued

As you go DOWN a hill on the ride, what kind of energy is being

transferred to what other kind?As you go UP a hill on the ride, what kind of energy is being

transferred to what other kind?

Energy transferred

How is energy transferred from the SUN, to you walking down the sidewalk?

If you hit a baseball, describe the energy changes occurring.

You throw a ball into the air. What energy transformations are taking place?

MOMENTUM

Momentum is mass X velocity

p = mv The unit is kg m/s

The Law of Conservation of Momentum

Momentum in a closed system is ALWAYS CONSERVED

Momentum “before” an event is equal to momentum “after” an event in the system

Classic examples are explosions, car crashes, pool balls, & shooting a gun.

Momentum conserved

In a collision, if one pool ball collides into another one that is at rest, pool ball 1 “shares” some momentum with pool ball 2

The TOTAL momentum of both pool balls added together is THE SAME before and after the collision

p = p’m1v1 = m2v2

The Impulse Momentum Theorem

CHANGE in momentum is EQUAL to Impulse

IMPULSE is equal to IMPACT (or force) times the TIME INTERVAL of the impact

p = Ft or (mv) = F t

Applications

Why is it better to bend your knees when you jump off a table?

Why do you move your hand backward when catching a fast pitch?

Why do air bags help?Why does a karate expert often try

to have a SHORT time of impact?

More applications

If you only want maximum velocity, such as trying to achieve maximum range of a golf ball, you should hit the ball with

a) a short time of impactb) a long time of impactc) it makes no difference

Applications continued

If a building is on fire and you want to minimize the force of impact on your bones when you jump from the 2nd story window, you should

a) land with straight legsb) land on your feet but bend kneesc) drop and roll to maximize time of

impact