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P2 3 Work, energy and momentum
- Energy and work
- Work is done on an object when
a force makes the object move
- The energy transferred
equals the work done
- Work done (in joules) = force (in
newtons) x distance moved in the
direction of the force (in metres)
- W = F x d
- W = F x d
- Work done to overcome friction is transferred
as energy that heats the objects that rub
together and the surroundings
- Work is done on an object when
a force makes the object move
- Gravitational potential energy (GPE)
- An object's GPE depends
on its weight and its height
- An object's GPE increases when
the object goes up and decreases
when the object goes down
- See notes for maths
- An object's GPE depends
on its weight and its height
- Kinetic energy
- A moving object's kinetic energy
depends on its mass and its speed
- See notes for maths
- Elastic potential energy is the
energy stored in an elastic object
when work is done on the object
- A moving object's kinetic energy
depends on its mass and its speed
- Momentum
- Momentum = mass (in kilograms)
x velocity (in metres per second)
- p = m x v
- Velocity is speed IN A
CERTAIN DIRECTION
- p = m x v
- Momentum is conserved whenever objects
interact in a closed system with no external forces
- This means the momentum after the interaction
equals the momentum before the interaction
- This means the momentum after the interaction
equals the momentum before the interaction
- The unit of momentum
is kilogram metres per
second (kg m/s)
- Momentum = mass (in kilograms)
x velocity (in metres per second)
- Explosions
- When two objects push each
other apart, they move apart ...
- ... with different speeds if
their masses are not the same
- The greater the mass,
the lower the speed
- The greater the mass,
the lower the speed
- ... with equal and opposite momentum
so their total momentum is zero
- ... with different speeds if
their masses are not the same
- When two objects push each
other apart, they move apart ...
- Impact forces
- When vehicles collide, the force of the
impact depends on mass, change of
velocity, and the duration of the impact
- The longer the impact time,
the lower the impact force
- Crumple zones and air bags increase the
impact time, so reduce the impact force
- Crumple zones and air bags increase the
impact time, so reduce the impact force
- The longer the impact time,
the lower the impact force
- When two vehicles collide...
- .. they exert equal and
opposite forces on each other
- ... their total momentum
is unchanged
- .. they exert equal and
opposite forces on each other
- When vehicles collide, the force of the
impact depends on mass, change of
velocity, and the duration of the impact
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