EnergyEnergy

Chap 4

Intro & Conservation

The Nature of EnergyThe Nature of Energy

4.1

What is Energy?What is Energy?

Every change that occurs (large or small) involves energy.

Changes are always taking place – light bulbs are heating the air the wind might be rustling leaves cars are driving down the road

What is Energy?What is Energy?

Energy is the ability to cause change. Anything that causes change must

have energy.The SI unit for energy is the joule

(abbreviated J)

Nature of EnergyNature of Energy

ENERGY

motion of electric charges

bonding of atoms

motion of objects

internal motion of particles

changes in the nucleus

The ability to cause change.

MECHANICAL

ELECTRICALCHEMICAL

NUCLEAR

THERMAL

joules (J)

An Energy AnalogyAn Energy Analogy

If you had $1000, you could put it in your wallet put it in the bank trade it for gold exchange it for travelers’ checks

Regardless of its form, money is money.

An Energy AnalogyAn Energy Analogy

In the same way, energy is energy – regardless of its form. Energy from the Sun that warms

you and energy from the food that you eat are only different forms of the same thing.

Nature of EnergyNature of Energy

Kinetic Energy (KE) energy a moving object has because

of its motion depends on mass and velocity

Nature of EnergyNature of Energy

KE = ½ mv2

KE increases as mass increases KE increases as speed increases

80 km/h

50 km/h

80 km/h80 km/h truck

50 km/h motorcycle

• Which has the most KE?

• Which has the least KE?

Nature of EnergyNature of Energy

Potential Energy (PE) stored energy depends on position or configuration

of an object

Nature of EnergyNature of Energy

• Which boulder has greater gravitational PE?

• What other ways can an object store energy?

PE = mgh PE increases as mass increases PE increases as height increases

Potential EnergyPotential Energy

There are several types of PE: Elastic PE

•Stretched rubber band Chemical PE

•Gasoline (bonds) Gravitational PE

•anything that can fall

• increases with height and mass

KE or PE?KE or PE?

An apple in a tree has PE.

An apple falling from a tree has KE.

Conservation of EnergyConservation of Energy

4.2

Conservation of EnergyConservation of Energy

Law of Conservation of Energy Energy can change from one form to

another, but the total amount of energy never changes.

6 Forms of Energy6 Forms of Energy Mechanical Thermal Energy Chemical Energy Electrical Energy Electromagnetic Energy Nuclear Energy

Transforming EnergyTransforming Energy

Light bulbs transform electrical energy into light and heat.

Transforming EnergyTransforming Energy

An engine transforms the chemical PE stored in gasoline molecules into the kinetic energy of a moving car or bus. spark plug fires (chemical PE into

thermal energy) Hot gases expand (thermal

energy into kinetic energy)

Transforming EnergyTransforming Energy

Some energy transformations are less obvious (no visible motion, sound, heat, or light)

Green plants convert light energy from the Sun into energy stored in chemical bonds in the plant

Conservation of EnergyConservation of Energy

PE KE The form of energy changes, but

the total amount of energy remains the same.

View pendulum animation.

Conservation of EnergyConservation of Energy

If energy is conserved, why do swings eventually slow to a stop? Mechanical Thermal

View rolling ball animations.

Your Body and EnergyYour Body and Energy

Everybody, raise both hands.In terms of energy, what happened?

PEKEEvery second, chemical PE (stored

when you eat) is converted into: Heat (constant body temperature

and given off to surroundings) Other daily functions (heart beat,

digesting, walking, etc.)

Your Body and EnergyYour Body and Energy

The food Calorie (C) is a unit used to measure how much energy you get from foods. 1 C = 4184 J 1 g of fat = 9 C 1 g of carbs or

protein = 4 C

Video and VLabVideo and VLab

http://www.brainpop.com/science/energy/formsofenergy/

http://www.brainpop.com/science/energy/kineticenergy/

http://glencoe.mcgraw-hill.com/sites/0078779626/student_view0/unit1/chapter4/virtual_lab.html

Self-Check 4Self-Check 4

1. 3 gram ball on a top shelf and a 3 gram ball on a bottom shelf. Which has more PE?

2. 2 gram ball and 6 gram ball move at 3 m/s. Which has more KE?

3. Friction converts ___________ energy into _________ energy.

top

6 gmechanical

thermal