Download Potential Energy

Energy Sources and Transfer of Energy:
Energy:
Energy is defined as the ability (or capacity) to do work. Energy is measured in joules. When a body has
300 J of energy it means that it can do 300 J of work.
It exists in different forms and when something happens, it is likely to be due to energy being
transferred from one form to another.
Energy transfer is needed to enable people, computers, machines and other devices to work and to
enable processes and changes to occur.
Different forms of energy:
Type of energy
Description
Kinetic energy
Gravitational potential
energy
Elastic potential
energy
Sound energy
Internal energy
Electrical potential
energy
Chemical potential
energy
Nuclear potential
energy
Type of energy Description
The ability to do work due to the movement of a body
The ability to do work due to the position of a body in a gravitational field
The ability to do work due to the deformation of a body (e.g. a compressed
or extended spring)
The ability to do work due to the kinetic and potential energy of the
vibrating particles in a sound wave
The ability to do work due the random kinetic and potential energy of the
particles in a body
The ability to do work due to a the position of a charged particle in an
electric field
The ability to do work due to potential energy of the particles making up
substances
The ability to do work due to the potential energy of the subatomic particles
in the nuclei of atoms
Principle of the conservation of energy:
The law of conservation of energy states that the total energy of a closed system is constant.
For examination purposes, you should explain this statement by saying that this means that energy can
be transformed from one form to another but it can neither be created nor destroyed — the total energy
of a closed system will be the same before an interaction as after it.
When energy is transformed from one form to another either:
Work is done — for example, a man does work against gravity by lifting a large mass onto his shoulders.
or
Energy is radiated or received in the form of electromagnetic radiation — for example, internal energy is
radiated away from the white hot filament of a lamp by infrared and light radiation.
Kinetic Energy:
Kinetic energy is the energy a body has because of its motion.
For a body of mass m travelling with velocity v, 𝐾. 𝐸. =
1
𝑚𝑣 2
2
Work–Kinetic Energy Theorem:
When work is done on a system and the only change in the system is in its speed, the net work done on
the system equals the change in kinetic energy of the system.
Work done = change in kinetic energy
Potential Energy:
Potential energy is the energy a body has because of its position or condition / shape.
Gravitational Potential Energy:
Energy possessed by an object due to its position in a gravitational field is called gravitational potential
energy. If mass of an object is m, and it is at a certain height h from ground, then
G.P.E = mgh
Elastic Potential Energy:
When a force causes an object to change its shape, the particles of the body are either squashed
together or pulled apart. Therefore, they have potential energy, called elastic potential energy.
𝐸𝑙𝑎𝑠𝑡𝑖𝑐 𝑃𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 =
1 2
𝑘𝑥
2
Conservation of Energy – Revisited:
A mass m at height h above the ground has potential energy mgh.
When it falls, its velocity increases and it gains kinetic energy at the expense
of its potential energy.
If it starts from rest and air resistance is negligible, its kinetic energy on
reaching the ground equals the potential energy lost by the mass.
1
𝑚𝑣 2 = 𝑚𝑔ℎ
2
Or
loss of P.E. = gain in K.E.
Renewable and non-renewable energy sources.
The ‘useful’ energy needs to be produced in controllable energy transfers.
For example, in power stations a supply of useful energy in the form of electricity is produced. The ‘raw
materials’ for energy production are energy sources.
These may be non-renewable or renewable. Apart from nuclear, geothermal, hydroelectric or tidal
energy, the Sun is the source for all our energy resources.
Renewable energy sources are not exhaustible. Their rate of generation is greater than rate of
consumption. For example, wind energy, tidal energy.
Non-renewable energy sources are exhaustible. Their rate of generation is less than their rate of
consumption. For example, we consume fossil fuels more as compare to their rate of production.
Energy Transfer:
(1) chemical/fuel energy (a re-grouping of atoms),
(2) hydroelectric generation (emphasising the mechanical energies involved),
(3) solar energy (nuclei of atoms in the Sun),
(4) nuclear energy,
(5) geothermal energy,
(6) wind energy.
Nuclear fusion and fission in terms of energy-releasing processes:
Electricity generation:
Draw a block diagram of the process from fuel input to electricity output.
Environmental issues associated with power generation.
Work done by a force:
Efficiency for an energy conversion:
Efficiency of energy conversions in processes giving electrical output:
Usefulness of energy output from a number of energy conversions:
Power:
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