Chapter 15

Energy: Forms and Changes

Nature of Energy Energy is all around you. Energy comes in the forms of

sound, light, and wind. Energy is defined as the ability to

do work. Energy is measured in Joules. (J)

Forms of Energy There are five main forms of

energy: Mechanical Heat Chemical Electromagnetic Nuclear

Mechanical Energy Matter that is

moving has energy. Energy that is

associated with motion is called mechanical energy.

Anything that is moving has mechanical energy.

Heat Energy All matter has

molecules that are constantly moving.

The more they move, the more heat is generated from friction.

The internal motion of atoms is called heat energy.

Chemical Energy Energy exists in

the chemical bonds of atoms.

When the bonds are broken, chemical energy is released.

Food and combusting gasoline release chemical energy.

Electromagnetic Energy Electromagnetic

energy is created by moving electric charges.

Electricity, light, x-rays, radio waves and laser light all have electromagnetic energy.

Nuclear Energy The nucleus, or

center of an atom is the source of nuclear energy.

When the nucleus of an atom splits or fuses together with another nucleus, nuclear energy is released.

Kinetic and Potential Energy Remember that everything has energy

because it is made of moving atoms. Potential energy is the stored energy of an

object that is not moving. Kinetic energy is called the energy of

motion. When an object is moving, it has kinetic energy. Which would have more kinetic energy, an elephant that weighs 8909 N or a mosquito that weighs .0098 N if they are both moving at the same velocity?

Kinetic energy The elephant

would have more kinetic energy because it has more mass.

The formula for kinetic energy is: K.E. = mass x velocity squared divided by 2.

Potential Energy Potential energy is

the energy of position.

A stretched rubber band has the potential to fly across the room, but as it is not moving it has potential energy rather than kinetic energy.

Gravitational Potential Energy Gravitational

potential energy is potential energy that is dependent on an object’s height above a surface.

A diver on a 3 meter board has 3 times the potential energy as a diver on a 1 meter board.

Weight and Gravitational Potential Energy Weight also determines the

gravitational potential energy of an object.

“The bigger they are, the harder they fall” is no exaggeration.

The formula for G.P.E is: G.P.E.= Weight x Height

Energy Conversions Changes in forms

of energy are called energy conversions.

The most common is the change of potential energy to kinetic energy and kinetic to potential energy.

Other Conversions All forms of energy can be

converted to other forms of energy.

For instance, when a match is lit what kind of energy is first released?

What kind of energy is that converted to?

Conservation of Energy The Law of Conservation of Energy states

that energy can neither be created nor destroyed by ordinary means.

Einstein’s theory of relativity: E=mc2

directly relates energy with mass. Einstein theorized that a great amount of energy could be formed from very little mass. Thus, energy and mass could be converted into one another.

Physics and Energy The topic of energy is

essential to learning about any subject in physical science.

Already you have studied it in terms of velocity, force, momentum and power.

How does energy relate to these topics?

Another quantity you have learned is work.

Work is directly related to energy.

What unit are both work and energy measured in?

Bouncing ball

Lasers and Energy