1. Energy

2. Menu Calculating Potential Energy Calculating Kinetic Energy
Conservation of Energy

3. How do we calculate Gravitational Potential energy?

4. Gravitational Potential Energy
This is energy when something is ‘out of position’. This rock climber has potential energy. The further she climbs – the more potential energy she would gain.
Water held behind a dam has this type of energy too.

5. How do we calculate Gravitational Potential Energy?
Potential Energy = mass x g x height PE
m x g x h

6. Calculate the Potential Energy of this Rock Climber
Her mass is 65 kilograms and she has climbed to a height of 84 metres

7. What is the mass of this rock climber?
His total potential energy is currently 192,000 J as he has climbed to a height of 320 metres
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8. How do we calculate Kinetic Energy?

9. Kinetic Energy This is energy due to motion.
All moving objects have kinetic energy
The faster they move (or the more mass they have) the more kinetic energy they have

10. Kinetic energy KE ½ x m x v2
Any object that moves will have kinetic energy.
To calculate the amount of kinetic energy an object has use the formula:
Kinetic energy = ½ x mass x velocity 2
J kg (m/s) 2 KE
KE = ½ mv2
½ x m x v2

11. Calculate the kinetic energy of this surfer
He has a total mass of 65kg and is travelling at a velocity of 7m/s

12. Kinetic energy = ½ x mass x velocity2
Answer
Kinetic energy = ½ x mass x velocity2
= ½ x 65 x 72
= ½ x 65 x 49
= J

13. Questions on Kinetic Energy
A girl of mass 40 kg is running at about 5m/s. What is her kinetic energy?
What is the kinetic energy of a 200g tennis ball thrown at a speed of 9m/s?
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14. Conservation of Energy

15. What is the Principle of ‘Conservation of Energy’?
ENERGY can never be CREATED or DESTROYED – it can only be CONVERTED from one form to another.
Another important principle is:
Energy is ONLY USEFUL when it is CONVERTED from one form to another.

16. Are energy conversions 100% efficient?
NO device is 100% efficient and the wasted energy is dissipated usually as HEAT & SOUND
Think of this washing machine. It gets noisy and hot when it is switched on to wash our clothes