1. WHEN G.P.E. IS CONVERTED
ENTIRELY TO K.E. OR VICE VERSA...
 Ek = ½mv2
 Ep = mgh
 By Principle of Conservation of Energy,
Ek = Ep
½mv2 = mgh
½v2 = gh
v = 2gh

2. 2
Principle of Conservation of Energy
and the non-ideal pendulum
1. Lost in EP  Gain in EK + Thermal energy (friction)
2. Lost in EK  Gain in EP + Thermal energy (friction)
Height gained is lower than the original because some of the energy
has been converted to thermal energy.
(1) (2)
The pendulum eventually comes to a stop.
Video -
Ballistic
pendulum

3. EFFICIENCY
What does efficiency refer to?

4. EFFICIENCY
 Recall Senoko Power Station:
 Note the conversion of energy from one
form to another

5. EFFICIENCY
 Do you agree?
The chemical energy of the fuel is fully
converted to electrical energy because
the Principle of Conservation of Energy
states that energy cannot be created
nor destroyed.

6. EFFICIENCY
 Some of the energy is converted to heat,
light and sound. The energy conversion is
thus not 100%
Wouldn’t this violate the
Principle of Conservation
of Energy?

7. EFFICIENCY
No, because the total sum of
heat, light, sound and electrical
energy is equal to the chemical
energy of the fuel

8. LIGHT BULB

9. EFFICIENCY
 In a system, the ratio of useful energy
output to the total energy input is
known as the efficiency of the system.
 Efficiency is expressed as a percentage

10. EFFICIENCY
 Calculate the efficiency of the light bulb.