This document defines key concepts related to work, energy, and power. It explains that work is force times distance, and defines units of work. It describes different types of energy like potential, kinetic, elastic, and chemical energy. Energy can change forms but is conserved. Power is the rate of doing work and is measured in watts. Moment, torque, and center of gravity are also defined in relation to rotational forces and equilibrium. Key concepts like Hooke's law, stress, strain, and thermal capacity are explained with mathematical formulas.

1. CHAPTER 4
Work, Energy, and Power

2. WORK
 Work is done when a force moves an object to which it acts in the
direction of the force
 Work = force x distance moved by force in the direction of the force
 Unit of work = Joule (J) or (force in newton x distance moved in
metre)

3. WORK DONE BY
EXPANDING GAS
 As gas expands, it does work by breaking down the masonry.
 Work done = pressure x change in volume
 When gas expands, work is done by the gas. If the gas contracts, then work is
done on the gas.
 Unit of work (J) = pressure (pascals/Pa) x changes in volume (m3)

4. ENERGY
 Energy is the ability to do work
Energy Notes
Potential energy Energy due to position
Kinetic energy Energy due to motion
Elastic or strain energy Energy due to stretching of an object
Electrical energy Energy associated with moving electric charge
Sound energy A mixture of potential and kinetic energy of
the particles in the wave
Wind energy A particular type of kinetic energy
Light energy Energy of electromagnetic wave
Solar energy Light energy from the sun
Chemical energy Energy released during chemical reaction
Nuclear energy Energy associated with particles in the nuclei
of atoms
Thermal energy Sometimes called heat energy

5. ENERGY
 Potential energy is the ability of an object to do work as a result of its
position or shape
 Work done = force x distance moved
= mxgxh
m- mass g- gravitational force
h- height of the distance moved

6. ENERGY
 Kinetic energy is energy due to motion.
 Ek=½mv2
m- mass v- velocity

7. ENERGY CONVERSION
AND CONSERVATION
Law of energy conversation:
 Energy cannot be created or destroyed. It can only be converted
from one form to another.

8. EFFICIENCY
 Efficiency gives measure of how much total energy may be used and is not
‘lost’
 Efficiency = useful work done ÷ total energy input

9. DEFORMATION OF SOLIDS
 Deformation – change of shape
tensile
Deformation
compressive
 Tensile – stretching of an object
 Compressive- pressing of an object

10. HOOKE’S LAW
 Hooke’s law stated that proved the elastic limit is not
exceeded, the extension of a body is proportional to the applied load.
 F= kΔL
F- force k – elastic constant (Nm-1)
ΔL- extension

11. STRAIN ENERGY
 Strain energy is the energy store in a body due to change of shape
 Strain energy W= ½k(ΔL)2
or
W= ½kx2

12. THE YOUNG MODULUS
 Young modulus is the constant that a particular material has that
enable us to find extensions knowing the constant and the dimension
of the speciment.
 Young modulus is = Stress ÷ Strain

13. STRAIN
 Strain is the ratio of two lengths, the extension and the original,
and thus it does not have unit.
 Stress= extension ÷ original length

14. STRESS
 The strain produced within an object is caused by stress.
 Tensile stress is the changes in length of the object
 Stress= Force ÷ area normal to force
 The unit of stress is (Nm-2) also known as Pascal (Pa)

15. SPECIFIC HEAT CAPACITY
 Specific heat capacity is the numerical value which a substance
needed to raise the temperature of unit mass of substance by one
degree.
 Q= mcΔt
Q- heat m- mass c- specific heat capacity
Δt- temperature change

16. THERMAL CAPACITY
 Thermal capacity is the numerical value of a body needs to raise
the temperature of the whole body by one degree
 Q=CΔt
Q- heat energy C- thermal capacity

17. SPECIFIC LATENT HEAT
 Specific latent heat is the numerical value of the quantity of heat
energy required to convert unit mass of solid to liquid (fusion) or
liquid to gas (vaporization) without any change in temperature.
 Q=mL
 L – specific latent heat

18. EXCHANGES OF HEAT
ENERGY
 Law of conservation of energy stated that energy applies in heat
energy gained by the colder object is equal to heat loss by the hotter
object.
 Energy gained= Energy lost

19. POWER
 Power is the rate of doing work and it’s a scalar quantity
 Power = work done ÷ time taken
 Power= force x speed
 Unit of power is watt

20. KILOWATT HOUR
 One kilowatt hour is the energy expended when work is done at
the rate of 1 kilowatt for a time of 1 hour.

21. MOMENT OF A FORCE
 The turning effect of a force is called moment of force
 The moment of force is defined as the product of the force and
the perpendicular distance of line of action of the force from the
pivot.

22. COUPLES
 A couples consist of two forces equal in magnitude but opposite
in direction of whose lines of action do not coincide.
 The torque of a couple is the product of one of the forces and the
perpendicular distance between the forces.

23. PRINCIPLE OF MOMENT
 The principle of moment stated that for a body to be in rotational
equilibrium, the sum of the clockwise moment about any point must
equal the sum of anticlockwise moment about the same point.

24. CENTRE OF GRAVITY
 The centre of gravity of an object is the point at which the whole
weight of the object may he considered to act.

25. EQUILIBRIUM
 Equilibrium :
• Sum of all forces in any direction must be 0
• Sum of moment of the forces about any point must be 0

26. RESOURCES
 International A/AS Level Physics by chris mee, mike
crundell, brian arnold, and wendy brown, published at 2008.

27. THE END
Jessica L
Grade 11 - Sci