ENERGY & POWER

Part 1The Nature of Energy

What is Energy?

• The ability to do work or cause change is called energy.

• OK…but what’s work?• Work is done when a force moves an

object through a distance.

TYPES OF ENERGY

• The two types of energy are KINETIC & POTENTIAL.

• What type you have depends on whether an object is moving or not.

KINETIC ENERGY

• The energy of motion is called kinetic energy.

I can’t swim

!

What Affects Kinetic Energy?

• K.E. depends on an objects mass and its velocity.

THINK: Which ball would you have to push harder to get rolling?

Once rolling the bowling ball would have more kinetic energy than a golf ball rolling at the same velocity.

CALCULATING KINETIC ENERGY

• KINETIC ENERGY = MASS x VELOCITY2

2Sometimes written (1/2)mv2

NOTICE: Changing the velocity of an object will have a greater effect on its kinetic energy than changing its mass. Why?

WHAT ARE THE UNITS?

• KINETIC ENERGY = MASS x VELOCITY2

2K.E. = kg x m2

s2

instead of saying all that we use the Joule!

SAMPLE PROBLEM• FIND THE K.E.A 10 kg wagon moving at 5 m/s• KINETIC ENERGY = MASS x VELOCITY2

210 x (5)2 divided by 210 x 25 divided by 2250 divided by 2

125… what were those units? kg.m2/s2 or JOULES

POTENTIAL ENERGY

• Potential Energy is energy that is stored and ready to use.

TYPES OF POTENTIAL ENERGY

• ELASTIC –the energy of an object that is stretched or compressed

GRAVITATIONAL POTENTIAL ENERGY

• Potential Energy That Depends on Height • G.P.E. = Weight (measured in Newtons) x

Height (measured in meters)

So..the units are NxM? YUP! Guess what? A NewtonMeter equals…A JOULE!!!

Uh…Wait a second.

• What if I don’t know an objects weight in Newtons?

• EASY: just multiply it’s mass (in Kg) times the acceleration caused by gravity (9.8m/s2)

Example: An object with a mass of 10kg would weigh how many newtons?

RIGHT! 98 Newtons!

G.P.E. Sample Problem

• A hiker weighing 680 Newtons climbs up a hill 40 meters high. How many Joules of G.P.E. has the hiker gained?

G.P.E. = Weight x Height680N x 40m= 27,200 Nm-OR- 27,200 Joules!

DIFFERENT FORMS OF ENERGY

• MECHANICAL• THERMAL• CHEMICAL• ELECTRICAL• ELECTROMAGNETIC• NUCLEAR

MECHANICAL• The energy

associated with motion or position of an object.

THERMAL

• The TOTAL energy of the particles in an object (kinetic + potential).

CHEMICAL

• The potential energy stored in chemical bonds that hold compounds together.

ELECTRICAL

• The energy of moving electric charges.

ELECTROMAGNETIC

• Energy That Travels in Waves.

NUCLEAR• A type of potential

energy• Stored in the nucleus

of the atom• Released during

nuclear reactions

Part 1 Check for Understanding

1. Are energy and work the same thing? Explain.

2. How are kinetic and potential energy different?

3. List the forms of energy and give an example of each.

4. A boulder the weighs 200N is sitting at the edge of a 100m cliff. What is its GPE?

• Work and energy are not the same thing, even though they are measured in the same units. Energy is the ability to do work. As work is done, energy is transferred from one object to another.

• Kinetic energy is the energy of motion. Potential energy is stored energy; it has the potential to do work.

• Mechanical – riding a bike

• Thermal – hot water

• Chemical – food

• Electrical – batteries

• Electromagnetic – TV Remote

• Nuclear – fusion in a star

• GPE = Weight x Height• GPE = 200 N x 100 m = 20,000 J

ENERGY & POWER

Part 2Energy Conversion &

Conservation

Part 2 Check for Understanding1. What is energy conversion?2. State the law of conversion of energy in your

own words.3. Describe the energy conversion that occurs

when a ball is dropped and bounces back up. Why does it bounce a little lower each time?

4. A roller coaster car with a mass of 500kg is at the top of a hill that is 30 m high. Without friction what would it KE be as it reached the bottom of the hill?

ENERGY & POWER

Part 3Energy Conversions & Fossil

Fuels

Part 3 Check for Understanding

1. How is the chemical energy in fossil fuels related to the sun’s energy?

2. How is the energy of coal released?3. Describe the energy conversions

involved in the formation of coal.4. What general statement can you make

about the supply of fossil fuels? (Hint: think about how they form).

ENERGY & POWER

Part 4Power

Part 4 Check for understanding

1. State the formula for calculating power.2. How are power and energy related?3. Find the work you do when you exert a

force of 40N to run a distance of 18m in 4 seconds. Now find the power you used.

4. The motor of an electric fan converts 24,000 J of electric energy every 60 sec. What is the power of the fan’s motor?

ENERGY

WORKJOULESKINETIC ENERGY

POTENTIAL ENERGY

ELASTIC GRAVITATIONAL POWER