1. Title: Kinetic and elastic energy
DO NOW
Describe, in a much detail as you can, what is happening to a ball as it rolls down a hill. Think about the energy changes.

2. Targeting GRADE 4 GRADE 6 GRADE 8
State the factors that affect the size of a kinetic energy store of an object.
State the factors that affect the elastic potential energy store of a spring.
Describe energy changes involving elastic potential energy and kinetic energy stores.
GRADE 6
Calculate the kinetic energy store of an object.
Calculate the elastic potential energy store of a stretched spring.
GRADE 8
Perform calculations involving the rearrangement of the kinetic energy equation.
Perform calculations involving the rearrangement of the elastic potential energy equation.
Perform a wide range of calculations involving transfer of energy.

3. amount of work done = amount of energy transferred
Work done = force x distance moved
When lifting things up the force is equal to it’s weight
Overall we can say
amount of work done = amount of energy transferred

4. Moving side to side
Imagine pushing a cart with very well-oiled wheels (no friction).
The speed of the cart will increase while the force acts.
work done = change in kinetic energy of the cart

5. kinetic energy = ½ mass  (velocity)2
The kinetic energy of a moving object depends on:
its mass (how big it is)
its speed (how fast it is moving).
The equation for calculating the kinetic energy of a moving object is:
kinetic energy = ½ mass  (velocity)2
KE = ½ mv2

6. Questions KE = ½ mv2 Which of the following has more kinetic energy:
a car of mass 500 kg travelling at 20 m/s
a car of mass 1000 kg travelling at 10 m/s
KE = ½ mv2

7. KE = ½ mv2 Which of the following has more kinetic energy:
a car of mass 500 kg travelling at 20 m/s
KE = ½ x 500 x 202 = 100,000 J
a car of mass 1000 kg travelling at 10 m/s
KE = ½ x 1000 x 10 m/s = 50,000J
So the lighter but faster car has more kinetic energy.

8. But what about when something stretches?
When you stretch and elastic band or spring the energy is stored as elastic potential energy
Lets picture a bungee jumper as an example……….

9. But what about when something stretches?

10. Investigating bungee jumpers
Set up the apparatus as shown at the front. Either clamp a metre ruler vertically as shown (using the set square to check the ruler is vertical), or set up graph paper behind the masses and measure positions by marking them on the graph paper.
Hold the masses at a fixed position near the point the rubber band is hanging from.
Record the position of the bottom of the mass holder against the metre ruler or graph paper.
Release the masses. Measure the lowest position of the bottom of the mass holder, and the highest position it rebounds to. Record all your measurements.
Repeat steps 2–4 two more times, using the same starting position of the masses.

11. But what about when something stretches?
We can calculate the energy stored in the bungee cord by calculating the elastic potential energy

13. Targeting GRADE 4 GRADE 6 GRADE 8
State the factors that affect the size of a kinetic energy store of an object.
State the factors that affect the elastic potential energy store of a spring.
Describe energy changes involving elastic potential energy and kinetic energy stores.
GRADE 6
Calculate the kinetic energy store of an object.
Calculate the elastic potential energy store of a stretched spring.
GRADE 8
Perform calculations involving the rearrangement of the kinetic energy equation.
Perform calculations involving the rearrangement of the elastic potential energy equation.
Perform a wide range of calculations involving transfer of energy.