WORK
Work is done when an object is moved by a force. The amount of work done is defined as the force F
multiplied by the distance s moved in the direction of the force.
i.e.
W = Fs
Where: W is work (J)
F is force (N)
S is distance moved in the direction of force (m)
The work done is a measure of the amount of energy transferred. E.g. when you lift a stone of mass m to
a vertical height h, the work done is mgh. This is the amount of chemical energy transferred to potential
energy of the stone.
POWER
It is the rate at which work is done or transfer.
work done /energy transfer
Power =
time taken
i.e
w
P= ===
t
Where: P is power (w)
W is work (J)
t is time (s)
ENERGY :It is the ability to do work.
TYPES OF ENERGY
(a) Chemical Energy: Sources include food, fossil (coal, oil and natural gas).
(b) Potential Energy: It depends on the raised position (gravitational potential) and strained
condition (elastic potential) of an object.
(c) Nuclear Energy: This is energy released from the nuclei of atoms.
(d) Sound Energy: This is energy produced by vibrating objects.
(e) Electrical Energy: It involves the flow of charges.
(f) Light Energy: Sources are sun, lamps, candles e.t.c.
(g) Kinetic Energy: Energy a body has because of its motion.
(h) Heat Energy: Sources are fires and sun.
MECHANICAL ENERGY
Examples of mechanical energy are kinetic and potential.
(a) KINETIC ENERGY: This is energy a body has because of its motion.
1 2
Ek = mv
2
Where: Ek is kinetic energy (J)
m is mass (kg)
v is velocity (m/s)
(b) POTENTIAL ENERGY : Energy a body has because of its position or codition.
Ep = mgh
Where: Ep is potential energy (J)
m is mass (kg)
g is gravitational field strength (N/kg or m/s2)
ENERGY CONSERVATION
The principle of energy conservation says “energy cannot be created or destroyed but it is
always conserved”. This means that energy can be changed from one form to another.
EXAMPLES
(a) MICROPHONE: Sound Electrical
(b) CATAPULT: Chemical Potential Kinetic
(c) HYDRO ELECTRIC POWER: Potential Kinetic Electrical
(d) BURNING CANDLE: Chemical Light + Heat
(e) ELECTRICAL KETTLE: Electrical Heat
CONSERVATION OF MECHANICAL ENERGY
In many machines there is a constant interchange between kinetic and potential energy. In a
frictionless machine, the total of the kinetic and potential would remain constant.
(a) ENERGY CHANGES OF A FALLING OR RISING OBJECT
If the total mechanical energy is conserved :
LOSS OF Ep = GAIN OF Ek OR GAIN OF Ep = LOSS Ek
(b) ENERGY CHANGES OF A SIMPLE PENDULUM
The kinetic energy Ek is great when v is greatest at C. Ep is greatest where bob is at its greatest
height h.
energy output
Efficiecy = x 100
energy input
(c) ENERGY CHANGES IN SOME DEVICES
(i) MICROPHONE: Sound Electrical
(ii)CATAPULT: Chemical Potential Kinetic
(iii)HYDRO ELECTRIC POWER: Potential Kinetic Electrical
(iv)BURNING CANDLE: Chemical Light + Heat
(v) ELECTRICAL KETTLE: Electrical Heat
(vi) SOLAR CELL: Light Electrical
(vii) LOUDSPEAKER: Electrical Sound
MAJOR ENERGY SOURCES IN BOTSWANA
(a) FOSSIL FUELS: These include coal, oil and natural gas.
(b) BIOMASS: These include crops, crop residue, animal dung and natural vegetation.
(c) SOLAR: Energy from the sun
(d) WIND: used to turn wind mills (turbines)
THE SOCIO – ECONOMIC AND ENVIRONMENTAL IMPACTS OF EACH ENERGY SOURCE
LOCALLY AND GLOBALLY
(a) FOSSIL FUELS
- Emits Sulphur Dioxide therefore causes acidic rain
- Emits Carbon Dioxide so increases greenhouse effect
- Limited fuel available(non-renewable)
(b) NUCLEAR
- Nuclear waste has to be disposed off safely
- Risks of big accidents
- Limited fuel available (non-renewable)
(c) SOLAR
- Unreliable because it depends on weather
- Solar cells are expensive
(d) HYDROELECTRIC
- Acts as a barrier to shipping routes
- Impossible in flat regions
- Floods large areas
- Affects ecology of an area when building the dam
- Expensive to build a dam
(e) BIOMASS
- Cutting down of trees leads to desertification
- Continual use of fertilizers and irrigation result in salination i.e soil becomes salty
(f) WIND
- Needs many large turbines over a large area.
- Noisy and unsightly
- Unreliable because wind does not blow everyday
(g) GEOTHERMAL
- Expensive
- Used where plates are stable
