Nature of EnergyNature 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!

ENERGYENERGY

• The energy released by a supernova is capable of destroying a nearby solar system in just a few hours.

A supernova is one of the greatest concentrations of energy in the universe.

There are two states of energy:

Potential (stored)

Kinetic (moving)

• Stored energy – energy of position.

• Not always mechanical energy – can be other forms.

• Gravitational Potential energy – dependent on height and weight.

• GPE = Weight x Height

• Units – Newton*meter

• The energy of motion.

• The faster the object moves – the more kinetic energy.

• Kinetic energy depends on both mass and velocity.

• KE = ½(mass x velocity2)

• Kg m2/s2 =Newton*meter= JoulesWhat is the kinetic energy of a 45 kg object moving at 13

m/sec?

1. KE = 1/2 mv2 KE = 1/2 (45 kg)(13 m/sec)2

2. Solving the equation gives a kinetic energy value of 3802.5 J

Practice Problems

1. A 6 kg rock is thrown with a velocity of 10 m/sec.  What is the kinetic energy of the rock?

2. A ball has 475 J of energy while in motion.  If the ball is moving at 30 m/sec, what is the mass of the ball?

3. A 1.8 kg cat climbs upwards 12 meters to sit on the roof of a house.  How much potential energy does it possess while it sits enjoying the sunshine?

4. A boulder has 5000 J of potential energy while sitting on top of a cliff.  If the cliff is 250 m above the ground, what is the weight of the boulder?

5. The boulder in problem 4 slides off the cliff, but lands on a ledge 50 feet below.  What is potential energy of the boulder now?

Forms of EnergyForms of Energy

• Energy appears in many forms.

There are several main forms of energy.

• Mechanical

• Heat

• Chemical

• Electromagnetic

• Nuclear

• Sound

• Light

Mechanical EnergyMechanical Energy

Energy of motion.

Examples:

• Water in a waterfall

• Wind

• Moving vehicles

• Sound

• Blood traveling through your body

Heat EnergyHeat Energy

• The internal motion of atoms.

• The faster the molecules move, the

more heat energy is produced.

Examples:

Changes in state of matter

Friction

• Energy that exists in the bonds that hold atoms together.

• When bonds are broken, chemical energy is released.

Examples:

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

• Sports… your body uses energy stored in your muscles obtained from food.

• Fire–a chemical change.

• Sodium metal reacts with water.

Chemical EnergyChemical Energy

http://www.projectgreenmachine.org/7F-chem.jpg

Electromagnetic EnergyElectromagnetic Energy

Moving electric charges.

Examples:

• Power lines carry electricity

• Electric motors are driven by electromagnetic energy

The magnets are strong enough to bear each other's weight when opposite poles are touching

The magnets can push each other along without touching, again when like poles are together

Nuclear EnergyNuclear Energy

• When the nucleus of an atom splits, nuclear

energy is released.

• Nuclear energy is the most concentrated

form of energy.

• Fission/fusion

http://www.dlt.ncssm.edu/TIGER/Flash/nuclear/Chain_Reaction.html

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

Sound EnergySound Energy

Sound energy relates to the compression and movement of molecules in a substance

sound waves travel in a given direction until an outside force or object gets in the way of its motion and

reflects it

sound waves can travel through different mediums, including solids, liquids, and gases

• The most common energy conversion

involves the changing of potential energy

into kinetic energy or vice-versa.

Examples:

Ball thrown in the air

Roller coaster

More Conversions

• All forms of energy can be converted to other forms.

• Law of Conservation of Energy:

Energy cannot be created or destroyed.

• Einstein – If matter is destroyed, energy is created,

if energy is destroyed, matter is created.

The total amount of mass and energy is conserved.

QuestionsQuestions

• What is energy?

• Can energy be transferred

from one object to another?

• What are the different forms

of energy?