Energy (transfer) Flashcards
'x' and '*' mean multiplication, '^' means superscript and '_' means subscript
Define Work
Work is the energy transfer that takes place when a force causes an object to move.
Or:
work done = force applied × distance moved in direction of force
(W = Fs)
W in Joules
F in Newtons
s in Meters
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How can Work be measured when force is applied at an angle
work done = force applied × distance moved in direction of force x cos(angle)
(W = Fscosθ)
W in Joules
F in Newtons
s in Meters
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Describe a Force - Distance Graph
A graph used for calculating work.
Since Work is the product of force and distance,
(Work = Force x Distance)
the area underneath the force distance line is equal to the work
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Define Energy
Energy is the measure of the ability of an object or a system to perform work.
There are many types of Energy.
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Define Kinetic Energy
The energy of an object, due to its speed
Or:
kinetic energy = ½ * mass * speed^2
(E_k = ½mv2)
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Define Gravitational Potential Energy
The energy of an object, due to its position in a gravitational field
Or:
gravitational potential energy = mass * gravitational field strength * height
(E_p = mgh)
often:
(ΔEp = mgΔh)
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Define Elastic Energy
The energy of an object, stored when it is stretched or compressed
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Define Chemical Energy
Energy stored in chemical bonds
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Define Nuclear Energy
Energy stored in nuclei
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Define Energy Transfer
The change of energy from one form to another
e.g. heat and sound when a car brakes, originating from friction
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State the first law of thermodynamics (the law of conservation of energy)
Energy cannot be created, or destroyed; it can only be changed into another form.
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Define Resistive Forces
Resistive forces are forces that act on a moving body in the opposite direction to the direction of movement.
e.g. friction, which includes drag and air resistance
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Define Power
Power is the rate at which work is done, or the rate at which energy is transferred.
Power is measured in Watts
Describe the Relationship between power, work done, and time taken
power = work done / time taken
W = ΔE_p + ΔE_k
where ΔE_p is positive when ΔE_k is negative and vice versa
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Define Efficiency (in the context of Work Energy and Power)
Efficiency is the ratio of useful work done by a device, to the total work done (or the ratio of useful output energy to the total energy input).
Or:
efficiency = useful work done / total work done
Or:
efficiency = useful energy output / total energy input
usually represented as a percentage
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Define a Sankey Diagram
A Sankey diagram is a type of flow diagram that shows the major energy transfers, including energy losses, through a closed system.
Remember, the intended output is always the one that continues towards the left, even if it is only 5%
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