ENERGY AND WORK P2 3.1
When a force moves an object, energy is transfered and work is done.
Whenever an object moves a force must have been appied. This supply must come from somewhere e.g electricity or fuel.
When work is done moving the object, the supplied energy is transfered to the object so the work done is equal to the energy transfered.
Work done = energy transfered.
Both work and energy used joule J.
Work done equation:
work done = force x distance moved in the direction of the force.
If no distance oves no work is done.
KINETIC ENERGY P2 3.2
Elastic potential energy is the energy stored in an elastic object when work is done on the object.
Kinetic energy is one which will go back to the original shape after being squashed or stretched.
Kinetic energy is the energy of movement.
The greater its mass the faster its speed, the more kinetic energy it has.
Kinetic energy J = 0.5 x mass kg x speed(squared) m/s2.
MOMENTUM P2 3.3
Momentum is calculated:
momentum kgm/s = mass kg x velocity m/s
Whenever objects interact, the total momentum before the interaction is equal to the total momentum afterwards, provided no external forces act on them.
This is called 'conservation of momentum'.
the interaction could be a collision or an explosion. After a collision the objects move off together, or they may move apart.
MORE ON COLLISIONS AND EXPLOSIONS P2 3.4
Momentum has size and direction.
When two objects are at rest their momentum is zero. In an explosion the objects move apart with equal and opposite momentum. One momentum positiove the other negative, so the total momentum after the explosion is equal.
The bullet moves off with a momentum in one direction and the gun recoils with equal momentum in the opposite direction.
CHANGING MOMENTUM P2 3.5
When a force acts on an object that is moving, or able to move, its momentum changes.
force = change in momentum / time taken for change.
For a particular change in momentum the longer the time taken for the change the smaller the force.
In a collision the momentum of an object often become zero durin the impact and the object comes to rest. If the impact time is short the forces on the object are large. As the impact time increases the force becomes less.
Crumple zones increases impact time and so reuces the force on the car and the people in it.