Work, Power and Efficiency - Topic 1 Flashcards
What is it meant by the term “work”
Work, Power and Efficiency
Work is the amount of energy shifted.
What is meant by mechanical work?
Work, Power and Efficiency
The energy shifted by a force
What are the units of work?
Work, Power and Efficiency
Joules, J
What is the equation for calculating mechanical work?
Work, Power and Efficiency
Work done = Force * distance
W = F * d
What force do you do work against when you lift an object onto a shelf?
Work, Power and Efficiency
Gravity
What force do you do work against when you push an object across a rough surface?
Work, Power and Efficiency
Friction
What force do you do work against when you push the opposite poles of two magnets together?
Work, Power and Efficiency
Magnetic force between the magnets
What is meant by the term power?
Work, Power and Efficiency
It is the rate of energy transfer (or the rate of work done).
This is the energy transferred (or work done) per second.
What are the units of power?
Work, Power and Efficiency
Watts, W
What is the equation for calculating power?
Work, Power and Efficiency
Power = Energy transferred/Time taken
One watt is the same as…
Work, Power and Efficiency
1 Joule per second.
What is meant by the term efficiency?
Work, Power and Efficiency
It is the fraction of the total energy that is useful.
What is the equation for efficiency, in terms of energy?
Work, Power and Efficiency
Efficiency = Useful energy/Total energy
What is the equation for efficiency, in terms of power?
Work, Power and Efficiency
Efficiency = Useful power/Total power
What are the units of efficiency?
Work, Power and Efficiency
Efficiency has no units, because it is a ratio.
Efficiencies are written as a decimal or a percentage.
What is the smallest value of efficiency?
Work, Power and Efficiency
0
What is the largest possible value of efficiency?
Work, Power and Efficiency
1
Explain why in practice it is impossible to have an efficiency of 1 for an energy transfer.
Work, Power and Efficiency
Because some energy is dissipated to other non-useful stores
State and explain how energy dissipation can be reduced for objects moving through air or water.
Work, Power and Efficiency
Make them more streamlined, to reduce the amount of drag/air resistance on the object
State and explain how energy dissipation can be reduced for surfaces moving against each other.
Work, Power and Efficiency
Lubricate the surfaces with oil, to reduce the amount of friction
State and explain how energy dissipation can be reduced for a house.
Work, Power and Efficiency
· Loft insulation
· Cavity wall insulation
· Double glazing
· Use materials with low thermal conductivity
Give an example of a material with a high thermal conductivity.
Work, Power and Efficiency
Metal
