P1 Energy And Energy Resources Flashcards
In what ways can energy be transferred?
Heating, waves, electric current, or when a force moves an object
Principle of conservation of energy
Energy cannot be created or destroyed
What is a closed system?
A system in which no energy transfers take place out of or into the energy stores of the system
Energy transferred=
Work done
Work done (J) =
Force applied (N) x distance moved along the line of action of the force (m)
Ep=
mgh
Change of gravitational potential energy store, ΔEp =
Mass, m x gravitational field strength, g x change of height, Δh
Unit for gravitational field strength
N/kg
The gravitational potential energy store of an object increases when…
It is lifted up as work is done on it to overcome the gravitational force
Kinetic energy, Ek =
1/2 x mass x speed^2
Ek=
1/2 x m x v^2
Elastic potential energy store, Ee=
1/2 x spring constant, k x extension^2, e^2
Ee=
1/2 x k x e^2
What is elastic potential energy
The energy stored in an elastic object when work is done on it
Useful energy
Energy that is transferred to where it is wanted in the way that it is wanted
Wasted energy
The energy that is not usefully transferred
As energy dissipates it gets
Less and less useful
Input energy
The energy supplied to the device
Useful output energy
The useful energy transferred by the device
Input energy=
Useful output energy+energy wasted
Efficiency
Useful output energy transferred by the device / total input energy supplied to the device
How to reduce friction between moving parts causing heating
Lubricate the moving parts to reduce friction
How to solve the resistance of a wire causing the wire to get hot when a current passes through it
In circuits, use wires with as little electrical resistance as possible
How to prevent energy waste from air resistance that causes a force on a moving object that opposes its motion
Streamline the shapes of moving objects to reduce air resistance
How to prevent energy transfer to the surroundings due to the sound created by machinery
Cut out noise (e.g. tighten loose parts to reduce vibrations)
What is power?
Rate of transfer of energy
Unit for power
Watts (W) or Kilowatts (kW)
Power (W) =
Energy (J) / time taken for energy to be transferred (s)
P=
E/t
Efficiency =
Useful power out / total power in
Power wasted =
Total power in - useful power out
