Law of conservation of energy
- energy cannot be created or destroyed
- it can only be transferred
Common energy transfers
- kinetic energy - in a moving object
- gravitational potential - in a falling object
- elastic - in a stretched or compressed object
- chemical - anything with a battery/ power source
- electical
- thermal
- light
Kinetic energy
- E = 0.5mv2
- E - kinetic energy (J)
- m - mass (kg)
- v - speed (m/s)
Gravitational potential energy
- E = mgh
- E - gravitational potential energy (J)
- m - mass (kg)
- g - acceleration due to gravity (9.8 m/s2)
- h - height (m)
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Elastic potential energy (given)
- E = 0.5ke2
- E - elastic potential energy (J)
- k - spring constant (N/m)
- e - extension (m)
Common question - final speed of a falling object
- work out gravitational potential energy at the top
- assume: K.E at the bottom = G.P.E at the top
- 😄 - most of the energy gets transferred when you drop the ball
- 😦 - some energy also gets transferred to other sources e.g. thermal energy/ used to overcome air resistance
- use the K.E equation to work out speed
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Efficiency
- efficiency = useful energy/ total energy
- efficiency = useful power/ total power
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