1.6 form 3 energy work and power

energy

by: Chris Lembalemba

(chrislembalemba@yahoo.com)

• “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?

PotentialEnergy

KineticEnergy

All Energy

GravitationPotentialEnergy

ElasticPotentialEnergy

ChemicalPotentialEnergy

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?

oEnergy that is stored and waiting to be used later

OTHER FORMS OF POTENTIAL ENERGY1. Elastic Potential Energy

o Potential energy due compression or expansion of an elastic object.

Notice the ball compressingand expanding

2. Chemical Potential Energyo 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.

ExerciseQ.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!