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Energy
4.1.1 Energy changes in a system and the ways
energy is stored before and after such changes
A system is an object or group of objects.
E.g. (example of changes in way energy is stored): when a ball is thrown up its
kinetic energy is transferred to it gravitational potential store.
Stores of energy:
Chemical - stored in chemical bonds
Kinetic - energy of moving object, increases with speed
Gravitational potential - energy of object at a height above the ground
Elastic potential -stored when objects are squeezed or stretched
Magnetic - two magnets are moved apart or closer together
Electrostatic - where two electric charges move closer or apart
Thermal - dependent on temperature
Nuclear - energy stored in nucleus. Where nuclei inside atoms decay or join.
Energy 1
, Energy pathways:
Mechanical work - a force moving an object through a distance (E.g. lifting an
object)
Electrical work - when an electric current flows (E.g. any electrical current)
Heating - due to a temperature difference (E.g. where an object gets warmer
or cooler)
Radiation - energy transferred as a wave (E.g. light radiation and infrared
radiation are emitted from the sun)
Work:
If a force is applied to an object over a distance, work is done on it. The work
done=energy transfer.
Work done (J) = force applied (N) x distance (m) W=fs
note: one joule = one newton-metre, and distance must be in the same
direction as force.
Power:
Is the rate of energy transfer so the rate at which work is done.
Power (W) = energy transferred (J) / time (s) P= W/t
note: one watt = one joule per second
Even if two systems transfer the same amount of energy, if one does it faster then
the power output is greater
Kinetic Energy:
Kinetic energy is directly proportional to mass
Kinetic energy is directly proportional to velocity squared.
Kinetic energy (J) = 0.5 x mass (kg) x velocity (m/s)^2 Ek = 0.5mv^2
Elastic Potential Energy:
Elastic potential energy (J) = 0.5 x spring constant (N/m) x extension (m)^2
Ep = 0.5ke^2
Energy 2
Energy
4.1.1 Energy changes in a system and the ways
energy is stored before and after such changes
A system is an object or group of objects.
E.g. (example of changes in way energy is stored): when a ball is thrown up its
kinetic energy is transferred to it gravitational potential store.
Stores of energy:
Chemical - stored in chemical bonds
Kinetic - energy of moving object, increases with speed
Gravitational potential - energy of object at a height above the ground
Elastic potential -stored when objects are squeezed or stretched
Magnetic - two magnets are moved apart or closer together
Electrostatic - where two electric charges move closer or apart
Thermal - dependent on temperature
Nuclear - energy stored in nucleus. Where nuclei inside atoms decay or join.
Energy 1
, Energy pathways:
Mechanical work - a force moving an object through a distance (E.g. lifting an
object)
Electrical work - when an electric current flows (E.g. any electrical current)
Heating - due to a temperature difference (E.g. where an object gets warmer
or cooler)
Radiation - energy transferred as a wave (E.g. light radiation and infrared
radiation are emitted from the sun)
Work:
If a force is applied to an object over a distance, work is done on it. The work
done=energy transfer.
Work done (J) = force applied (N) x distance (m) W=fs
note: one joule = one newton-metre, and distance must be in the same
direction as force.
Power:
Is the rate of energy transfer so the rate at which work is done.
Power (W) = energy transferred (J) / time (s) P= W/t
note: one watt = one joule per second
Even if two systems transfer the same amount of energy, if one does it faster then
the power output is greater
Kinetic Energy:
Kinetic energy is directly proportional to mass
Kinetic energy is directly proportional to velocity squared.
Kinetic energy (J) = 0.5 x mass (kg) x velocity (m/s)^2 Ek = 0.5mv^2
Elastic Potential Energy:
Elastic potential energy (J) = 0.5 x spring constant (N/m) x extension (m)^2
Ep = 0.5ke^2
Energy 2
