Topic 8 - Energy - Forces doing work Flashcards
When systems change
Energy is transferred
A system is
An object or group of object
Some energy is always
Dissipated or stored in less useful ways
Efficiency is
The proportion of total energy supplied that ends up in useful stores
When there are energy transfers in a closed system
There is no net change to the total energy
The energy of a system is changed by
Heating
Forces doing work
Electrical equipment
Energy transfer diagrams show
The original energy store
The way the energy of the system was changed
The energy store(s) that it ends up in
If a force moves an object through a distance
Work is done and energy is transferred
Energy transferred(j) is equal to
Work done(j)
Work done(j) =
Force(n) x Distance moved(m)
One joule of work is done when
A force of 1N moves and object 1m
1J =
1Nm
Change in GPE (J) =
Mass(kg) x gravitational field strength(N/kg) x Change in height(m)`
Kinetic energy (J) =
1/2 x mass(kg) x velocity^2 (m/s)
Examples of waste energy stores
Electric toothbrush - Wasted sound and heating
Hair dryer - Sound and heating
Mechanical processes become wasteful when
The cause a rise in temperature so energy dissipates into surroudnings by heating
Power(W) =
Work done(J) / Time taken(s)
Power is
The rate of energy transfer
1W =
1 J/s
Effiency =
Useful energy transferred/Total energy supplied
