energy

• “the ability to do work”

• The combination of energy and matter

make up the universe:

– Matter is substance, and energy is the

mover of substance.

What is energy?

The Law of Conservation of

Energy

• Energy cannot be created or destroyed; it

may be transformed from one form into

another, but the total amount of energy

never changes.

Energy is

nature’s way of keeping score.

We sense energy only when the score changes,

either a transformation from one form of energy to another,

or a transfer of energy from one point to another.

How is all energy divided?

Potential

Energy

Kinetic

Energy

All Energy

Gravitation

Potential

Energy

Elastic

Potential

Energy

Chemical

Potential

Energy

Potential Kinetic

• energy of position

or energy in

storage.

– Water behind a dam

– Hammer over head

– Food on the plate

• energy of motion,

the form capable of

doing work

– Flowing water

– A falling hammer

– Electrons regenerating

ATP in a bio’l cell

What is Gravitational Potential Energy?

o Potential energy due to an object’s position

o G,P.E. = mass x

height x gravity

Don’t look down,

Bingo!

Good boy!

GPE = mgh

• m = mass (kg)

• h = height (m)

• g = acceleration due to

gravity (10 m/s2)

Example .1

• How much gravitational potential

energy is lost by a 5Kg object to

kinetic energy due a decrease in

height of 4.5 m

• GPE = mgh

• GPE = (5Kg) x(10 m/s2)x (4.5 m)

• GPE = 225 J

10.3 Potential Energy

• A cart with a mass of 102 kg is

pushed up a ramp.

• The top of the ramp is 4 meters

higher than the bottom.

• How much potential energy is

gained by the cart?

• If an average student can do 50

joules of work each second,

how much time does it take to

get up the ramp?

1. An object has a mass of 1500g. What is

its gravitational potential energy

1. 4m above the ground

2. 650cm above the ground

2. How high should a car of mass = 15

tonnes be to have a GPE of 2.0x106J?

What is Potential Energy?

o Energy that is stored

and waiting to be

used later

OTHER FORMS OF POTENTIAL ENERGY

1. Elastic Potential Energy

o Potential energy due compression or

expansion of an elastic object.

Notice the ball compressing

and expanding

2. Chemical Potential Energy

o Potential energy

stored within the

chemical bonds of

an object

•

3. Mechanical energy is the energy possessed by

an object due to its motion or its position.

4. Radiant energy includes light, microwaves, radio

waves, x-rays, and other forms of

electromagnetic waves. It is also called

electromagnetic energy.

5. Nuclear energy is released when heavy atoms in

matter are split up or light atoms are put

together.

6. The electrical energy we use is derived from

other sources of energy.

What is Electrical Energy?

o Energy caused by

the movement of

electrons

o Easily transported

through power lines

and converted into

other forms of

energy

What is Thermal Energy?o Heat energy

o The heat energy of an

object determines how

active its atoms are.

A hot object is one whose

atoms and molecules are

excited and show rapid

movement.

A cooler object's molecules

and atoms will show less

movement.

What is the source of our

energy?

• The source of

practically all

our energy is

the Sun.

Kinetic Energy

• Energy of motion is called kinetic energy.

• The kinetic energy of a moving object

depends on two things: mass and speed.

• Kinetic energy is proportional to mass.

Kinetic Energy

K.E = 1

mv2

2

Speed (m/s)

Mass (kg)

Kinetic Energy

(Joules)

KE = 1/2 m v2

• 4 kg bowling ball

• at 10 m/s

• = .5 (4kg) (10m/s)2

• = 200 J

• .25 kg baseball

• at 50 m/s

• = .5 (.25kg) (50 m/s)2

• = 312 J

Law of Conservation of Energy

• As energy takes different forms and

changes things by doing work, nature

keeps perfect track of the total.

• No new energy is created and no existing

energy is destroyed.

5.3 Energy Transformations

Key Question:

Where did the energy go?

A 5kg block falls from a height of 12m.

Calculate:

a. The G.P.E that the block had before the

fall.

b. The K.E in the block just before hitting the

ground.

c. The velocity with which the block hits the

ground.

Exercise

Q.1.

Q.2.

A car with a mass of 1,300 kg

is going straight ahead at a

speed of 30 m/sec (67

mph).

The brakes can supply a force

of 9,500 N.

Calculate:

a) The kinetic energy

of the car.

b) The distance it takes

to stop.

PREP

A ball has a mass of 0.75kg. Dropped from a cliff

top, the ball hits the sea at a speed of 10m/s.

a. What is the kinetic energy of the ball as it is

about to hit the sea?

b. What was the ball’s gravitational potential

energy before it was dropped?

c. From what height was the ball dropped?

d. A stone of mass 1kg also hits the sea at 10m/s.

repeat stages a, b, and c above to find the

height from which the stone was dropped.

Energy and Conservation of Energy

Key Question:

How is motion on a

track related to

energy?

Application: Hydroelectric Power

Thank you!