7. POWER
ENERGY
WORK

8. WHEN ENERGY IS TRANSFORMED FROM ONE FORM TO ANOTHER
WORK IS DONE
WHEN ?
WHEN ?
WHEN ENERGY IS TRANSFORMED FROM ONE FORM TO ANOTHER

9. UNITS OF WORK & ENERGY ? mJ kJ
JOULES GJ MJ
Symbol J

10. FORMS OF ENERGY ENERGY IS A SCALAR ELECTRICITY Gravitational &
MAGNETISM
Gravitational
Potential
HEAT
Chemical
Potential
Sound
LIGHT
Nuclear
kinetic
ENERGY IS A SCALAR

11. THE PRINCIPLE OF
CONSERVATION OF ENERGY
ENERGY CAN BE CHANGED FROM ONE FORM TO ANOTHER, BUT CAN NEVER BE DESTROYED

12. heat
heat
potential
chemical
electromagnetism
kinetic
sound
light

13. What energy changes occur here?

14. WORK DONE = FORCE X DISPLACEMENT
Work (W) is done when a force (F) moves an object between two positions.
WORK DONE = FORCE X DISPLACEMENT
W = F d
Force F
Force F
Displacement d

15. W = F·d·Cosθ
Force F θ
Displacement d

16. Eg = mgh Work done = Potential Energy change h mg
Formula for (gravitational) Potential Energy Eg h
Work done = Potential Energy change
Eg = mgh mg

17. EK = ½ m v2 Formula for Kinetic Energy - EK d F Final velocity vf
Mass m
Initial velocity vi=0 F
EK = work done in accelerating to velocity, vf. i.e EK = Fd
vf2 = vi2 + 2 ad = 2 ad [as vi = 0]
EK = m a d
as F = ma
EK = ½ m v2

18. JOULES / SECOND = WATTS ( W )
POWER is the
RATE OF DOING WORK
= RATE OF CONVERTING ENERGY
UNITS
JOULES / SECOND = WATTS ( W )

19. The efficiency [ e ] of a machine is the power output (or energy output) divided by the power input (or energy input), usually expressed as a percentage.
If a kW electric motor lifts a load 2.00 kg though a distance of 3.00 m in 2.00 seconds, its efficiency is given by:

20. P = F v For a vehicle moving at constant velocity, v.
Where F is the driving force of the engine. F
The power to maintain this velocity is given by :
P = F v

21. s FINDING ONE’S POWER x (Sx) m Height of step = x m Height of steps =
My weight in Newtons = y N
Time to ascend = z s
MY POWER = (ySx/z) W
746 W = 1 hp