EnergyEnergy

Nature of Energy• Energy is all around you.• You hear energy as sound,

you see energy as light, you can feel energy in wind.

• Living organisms need energy for growth and movement.

• You use energy when you hit a tennis ball, compress a spring, or lift a grocery bag.

• Energy is the ability to do work.

Forms of Energy• Energy appears in many forms.• There are five main forms of energy.

– Mechanical– Heat– Chemical– Nuclear– Electromagnetic

• Electrical

Mechanical Energy• The energy possessed by an object

due to its motion or position.• Mechanical Energy is equal to

potential energy plus kinetic energy.– ME = PE + KE

• Examples:– A thrown baseball– Water in a waterfall

Heat Energy• The internal motion of atoms.• The faster the molecules move, the

more heat energy is produced.

Examples:FrictionChanges in state of matter

Chemical Energy• Energy that exists in the bonds that hold

atoms together.• When bonds are broken, chemical energy

is released.

• Digesting food…bonds are broken to release energy for your body to store and use.

• Fire…a chemical change.

Examples:

Nuclear Energy• The potential energy stored in the

nucleus of an atom.• When the nucleus of an atom splits,

nuclear energy is released.• Nuclear energy is the most

concentrated form of energy.

Electromagnetic Energy

• Light is this form of energy (X-rays, radio waves, laser light, etc.)

Example:

Energy that travels in waves, such as ultra-violet radiation. It can be thought

of as a combination of electric and magnetic

energy.

Electrical Energy• The energy associated with electric

charges.• Power lines carry electrical

energy into your house = electricity.

• Batteries

Examples:

Each of these forms of

energy is a combination of

PE & KE.

Questions• What is energy?• What are the different forms of

energy?• Can energy be transferred from one

object to another?

States of EnergyThere are two

states of energy: Potential and

Kinetic

Potential Energy• A stretched rubber band has energy.• Two magnets, when pulled apart,

have energy.– The rubber band has energy because

it’s stretched rather than relaxed.– The magnets have energy because

they’re apart rather than together.

Potential EnergyWhen something, or a group of

things, has energy simply because of relative position or shape, it’s known as potential

energy.• A stretched rubber band has PE and thus the ability to do something…– snap back into place if you let go.

• Two separated magnets have PE and thus the ability to do something…– jump back together when you let them go.

Potential Energy• Gravitational Potential Energy

(GPE) – the PE everything has because of its height above the Earth’s surface.

• GPE = m g h (where m equals the mass of the object, g equals 9.8 m/s2, and h equals the height of the object above some surface)

Kinetic Energy• Anything that is moving has

a special kind of energy known as “moving energy.”

• This “moving energy” is called kinetic energy.– A rolling ball, a running dog, a

falling object, two magnets heading towards each other, and anything else in motion, all have kinetic energy.

– The faster the object moves, the greater the kinetic energy.

Kinetic Energy• The kinetic energy of an object

depends on both its mass and its velocity.– KE increases as mass increases.– KE increases as velocity increases.

• Kinetic energy = ½ mass x velocity2

– KE = ½ mv2

Energy Conversions

The most common energy

conversioninvolves the changing of

potential energy into

kinetic energy or vice-versa.

1

2

3

1. At the top of the ramp, the marble’s ME is equal to its PE because the marble has no velocity.• 100% PE

2. As the marble goes down the ramp, it loses height but gains speed. The PE lost is equal to the KE gained.• 50% PE & 50% KE

3. As the marble speeds along the bottom of the ramp, all of the PE has changed to KE. Total ME remains unchanged.• 100% KE

Energy Conversions• The Law of Conservation of Energy states

that energy cannot be created or destroyed, BUT can be converted into other forms of energy.

• No matter how energy is transformed or transferred, all of the energy is still present somewhere in one form or another.

• As long as you account for all of the different forms of energy involved in any process, you will find that the total amount of energy never changes.

Your body converts chemical energy stored in food into thermal

energy & mechanical energy

(muscle movement).

ENERGY