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Energy

The ability of a system to do work.

Two types of energy:

•Kinetic Energy

•Potential Energy

States of Energy

All forms of energy can be in either of two states:

KINETIC ENERGY

POTENTIAL ENERGY

What’s the difference?

Kinetic Energy is the energy of MOTION

Potential Energy is STORED energy.

Kinetic Energy – what does it depend on?

The an object moves, the it has.

The greater the of a moving object, the

it has. Kinetic energy depends on both

faster more kinetic energy

massmore kinetic energy

mass and velocity.

Calculating Kinetic Energy

What has a greater affect of kinetic energy, mass or velocity? Why?

25.0 velocitymassKE

What is the unit for Kinetic Energy?

Unit: Joule

Named after: James Prescott Joule He discovered the relationship between heat

(energy) and mechanical work which led to the law of conservation of energy.

How do we derive this unit? 1 Joule = 1kg m2/s2

KE = ½ m(kg) v(m/s) 2

Some types of Potential Energy include…

Gravitational potential energy

Elastic potential energy - Stored energy due to

- stored energy due to an objects position (height)- depends on mass of the object and its distance from earth.

- Stored energy due to compression or expansion of an elastic object

Calculating Potential Energy

OR you could multiply weight (in Newton’s) by height

PE mass gravity height

What unit do we use for Potential Energy?

Unit: Joule

How do we derive this unit? 1 Joule = 1kg m2/s2

PE = m(kg) g (m/s2 ) height (m)

1. You serve a volleyball with a mass of 2.1 kg. The ball leaves your hand with a speed of 30 m/s. The

ball has ___________ energy. Calculate it.

2. A baby carriage is sitting at the top of a hill that is 21 m high. The carriage with the baby weighs 12

N. The carriage has ____________ energy. Calculate it.

3. A car is traveling with a velocity of 40 m/s and has a mass of 1120 kg. The car has

___________energy. Calculate it.

4. A cinder block is sitting on a platform 20 m high. It weighs 79 N. The block has _____________ energy.

Calculate it.

 5. A roller coaster is at the top of a 72 m hill and weighs 966 N. The coaster (at this moment) has

____________ energy. Calculate it.

6. Two objects were lifted by a machine. One object had a mass of 2 kilograms, and was lifted at a speed of 2 m/sec. The other had a mass of 4 kilograms and was

lifted at a rate of 3 m/sec.

a. Which object had more kinetic energy while it was being lifted? 

b. Which object had more potential energy when it was lifted to a distance of 10 meters? Show your

calculation.

As a basketball player throws the ball into the air, various energy conversions take place.

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Law of Conservation of Energy

Energy can be neither created nor destroyed by ordinary means.

Energy can be from one form to another.

The total amount of is the before and after any transformation or

transfer.

energy same

transformed or transferred

Energy Transfer

Energy TRANSFER is the passing of energy from one object to another object.

Example: A cup of hot tea has thermal energy. Some of this thermal energy is transferred to the particles in cold milk, in which you put to make the coffee cooler.

Energy Transformation

A change from one form of energy to another.

Single Transformations Occur when form of needs to be

into another to get work done.

Multiple Transformations Occur when a of energy transformations are

needed to do

one energy transformed

serieswork

Energy Transformation

An objects energy can be:

As velocity kinetic energy and potential energy

As velocity kinetic energy and potential energy

1. All Kinetic Energy2. All Potential Energy

3. A combination of both

increases increases

increasesdecreases

decreasesdecreases

WHAT IS THE TYPE OF RELATIONSHIP KE AND PE HAVE? INVERSE

Roller CoastersDoes energy get transferred

or transformed?

http://www.youtube.com/watch?v=8abzpXCjyjA

• As you move up to the first hill on a roller coaster the distance between the coaster and the Earth increases, resulting in an increase of Gravitational Potential Energy.• At the top of the first hill you have the most Gravitational Potential Energy• As you begin your trip down the hill you increase your speed resulting in a transformation from GPE to KE.• At the bottom of the hill right before it goes back upward the GPE is small, but the KE is Large.• As it starts to move up the next hill or loop KE is transformed back into GPE