physics power point

Relative Velocity and Frame of Reference

Frame of Reference

Motion is a change in position relative to a frame of reference

Frame of reference: a set of objects used to measure a change in position.1. Standing frame of reference2. Moving frame of reference.

Speed vs Velocity

Speed is the distance an object travels in a time period.▪ S = d/ t ▪ Units m/s

Velocity of an object is the speed and direction of motion. Ex: A car travels 60 m/s north on I-75 and then

turns around and goes south at 60 m/s. Does the car have the same speed? Same velocity?

Ans: Same speed, different velocities b/c different directions

Relative Speed/ Velocity

Relative speed and velocity depend on a frame of reference.1. Standing frame of reference

a. Objects moving in the same directions, add (+) speeds

b. Objects moving in opposite directions, subtract (-) speeds

Relative Speed/ Velocity

1. Moving frame of referencea. Objects moving in the same directions,

subtract (-) speedsb. Objects moving in opposite directions, add

(+) speeds

Calculating Relative Speed Flowchart

What is the frame of

reference?

Standing

Same direction

“+”

Opposite directions

“−”

Moving

Same direction

“−”

Opposite directions

“+”

Newton’s Gravitational Force

Force of Gravity

Gravitational force – attractive force that any two objects having a mass exert on each other. On Earth, gravitational force is equal to

the mass of the object times the gravitational constant (accelaration)▪ F = mg▪ Units = kg m/s2 newtons (N)▪ Earth average g= 9.81 m/s2

▪ Gravitational force = weight

Review

Mass vs. Weight Mass – amount of matter in an object▪ Units = kilogram (kg)

Weight- how heavy something is. ( gravity applied on the mass of an object) ▪ Units = Newton (N) ▪ Newton is a derived unit (kg m/s2 )

Universal Law of Gravitation Universal Law of Gravitation(ULG) – used

to describe attractive force between large objects such as the planets and the sun.

G has constant value of 6.67 x 10-11 N m2/kg2

m1 = mass of object 1

m2 = mass of object 2 d = distance between two objects

Using the ULG

Ex: A satellite orbits Earth at a distance of 72 km. If the satellite were to orbit Earth at a distance of 144km away from the center of the Earth, by how much would the force between the satellite and the Earth change.a. The force would be 4 times greaterb. The force would be 2 times greaterc. The force would be 2 times smallerd. The force would be 4 times smaller

Using the ULG

Solution:

Proportions

Proportions are relationships between two or more things.

To find relationships divide (÷)or create a ratio (fraction)

Direct relationships are shown as follows X = Y If x increases, y increases

Inverse relationships X = 1/Y If Y increases, X decreases

Using the ULG

Ex2: Two one kg spheres are 1 meter apart. Which of the following would double the gravitational force between them?a. Doubling the mass of one sphereb. Doubling the mass of both spheresc. Halving the distance between both

spheresd. Doubling the distance between both

spheres

ULG

Ex3: Two 20 kg spheres are 15 meters apart. Which of the following will give a gravitational force that is ¾ of the original force?a. Double both masses, leave the distance the

same.b. Triple one mass, double the distance between

themc. Triple both masses, double the distance between

themd. Double both masses, double the distance

between them.

Energy

Types of Energies

Radiant Energy- energy from the sun in the form of electromagnetic waves (light)

Electrical Energy – energy of flowing electric particles, current.

Heat Energy – energy transferred by a difference in temperature

Chemical Energy – energy given off by chemical reactions

Types of Energies

Kinetic Energy – energy that an object has due to its motion KE = ½ mv2

Units = kg m2/s2 Joules (J)

Potential Energy – stored energy that an object has due to its position PE = mgh Units = kg m/s2 m Joules (J)

Types of Energies

Mechanical energy – energy used to perform work

Practice

Energy Transformations

During phase changes, energy is either absorbed or released.

Energy Flow & Transformation Energy from the sun is captured by the green plants, (trophic level I)transformedinto chemical energy through photosynthesis and passed on through the various trophic levels.

The flow of energy is unidirectional i.e., non-cyclic.

Some energy is lost in theform of heat at every statein the atmosphere. Energy pyramid

9. Buzz Lightyear is on a mission to save his home planet Galactika. A giant blazing meteor with a mass of 2.5 x 10^8 kg is creeping dangerously close to Galactika, whose mass is of 5.56 x 10^23 kg. It is currently at a distance of 6.99 x 10^3 km from his planet. Woody helped Buzz create the Mega Meteor Blaster to save Galactika. If Buzz uses the blaster on the meteor it will decrease the mass of the meteor by 4 but also push the meteor closer to the planet, cutting the distance between Galactika and the meteor in half. Time is ticking and Buzz needs your help to decide if he should use the Mega Meteor Blaster. Should he use the Blaster and what would happened to the force between Galactika and the meteor if he did?