What happens to the gravitation force on an object as it gets closer

to another object?

Agenda for Monday Nov 10th 1.Quiz2.Energy Notes

Nature of Energy

• Energy is all around!– Sound– Light– Wind

• Living organisms need energy

Nature of energy• Energy is involved when– A bird flies– A bomb explodes– Rain falls– Electricity flows through a wire

Law of Conservation of Energy

• Energy cannot be created or destroyed– It can only be converted from one form to another

• 1905, Albert Einstein said mass and energy can be converted into each other– Matter is destroyed, energy is created and vice

versa– E = mc2

Nature of energy

• Energy is the ability to do work– If something does work (exerts a force over a

distance) it uses energy

• Direct connection between energy and work– measured in the same unit: Joules (J)

Forms of Energy

• 5 main categories– Heat– Chemical– Electromagnetic– Nuclear– Mechanical

1. Heat Energy

• Internal motion of the atoms– Moving particles produce heat

• Heat energy can be produced by friction

• Heat energy causes changes in temp. and phase of any form of matter

What is the law of conservation of energy?

Agenda for Tuesday Nov 11th 1.Finish notes2.Problems on GE/KE

2. Chemical Energy

• Energy that is available for release from chemical reactions.

• The chemical bonds in a matchstick store energy that is transformed into thermal energy when the match is struck.

• Fuel and food

Examples of Chemical Energy

3. Electromagnetic Energy

• Gamma rays, x-rays, ultraviolet rays, visible light, infrared rays, microwave and radio bands

• Power lines carry electromagnetic energy in the form of electricity

• Light - each color (ROYGBIV) is a different amount of energy

4. Nuclear Energy

• Nucleus of an atom is the source of nuclear energy

• SUN– Fission & Fusion

5. Mechanical Energy• Energy due to a object’s motion

(kinetic) or position (potential)• When work is done to an object, it acquires

energy• When you kick a football, you give mechanical

energy to the football to make it move

Energy Conversion

• Energy can be changed from one form to another– Changes in the form of energy are called energy

conversions

• All energy forms can be converted to other forms– Sun through solar cells to electricity– Plants take sun energy to sugars (electromagnetic to

chemical)

States of Energy

• Most common energy conversion is between potential and kinetic energy

• All forms of energy can be in either of 2 states– Potential– Kinetic

Kinetic Energy

• Kinetic Energy – energy of motion– Depends on mass and velocity– Faster an object moves, more kinetic energy it has– Greater the mass, more kinetic energy it has

• KE – 1/2mv2

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

Potential Energy

• Potential energy – stored energy– Fuel, nucleus, food– Stored because of the work done on it:• Stretching a rubber band• Winding a watch• Pulling back on a bow’s arrow• Lifting a brick high in the air

• Energy that is stored due to being stretched or compressed is elastic potential energy

Gravitational Potential Energy

• Potential energy that is dependent on height– Waterfall– Suspension Bridge– Falling snowflake

• GPE = weight x heightOr• GPE = mgh

Gravitational Potential Energy

• If you stand on a 3 meter diving board, you have 3 times the GPE than you had on a 1 meter diving board

Kinetic - Potential Energy Conversions

• Roller Coaster– Mechanical energy brings them to the top– This gives them great potential energy– Conversion between potential to kinetic energy

powers cars through the entire ride

• At the point of max PE, the car has minimum KE

Kinetic - Potential Energy Conversions

• As a baseball player throws the ball into the air, various energy conversions take place

Which has more gravitational potential energy: a ball on a 5 m

cliff or a ball on a 10 m cliff? Why?

Agenda for Wednesday Nov 12th 1.Bouncing ball lab

All late work due Wednesday Nov 19th

Where is the most kinetic energy?Most potential energy?

Agenda for Thursday Nov 13th 1.KE/GPE Problem set

A

D

C

B

Equations for Energy

Practice Problems

1. A 800g ball is lifted 20 cm. Calculate the potential energy it gains.

2. A man climbs on to a wall that is 3.6m high and gains 2268J of potential energy. What is the mass of the man?

1. Determine the kinetic energy of a 625-kg roller coaster car that is moving with a speed of 18.3 m/s.

2. What is the kinetic energy of a 0.50 kg ball travelling at a speed of 120 m/s ?