Physics 2.3

Physics 2.3

Energy and work
1. When a force moves an object, work is done
2. Energy transferred= work done
  1. Work=force x distance
3. Work done to overcome friction is transferred to heat energy
Gravitational potential energy
1. The gpe of an object depends on its weight and how far it moves vertically
2. change in gravitational potential= massXgravitational field strengthXchange in height
3. Power is the rate of transfer of energy
  1. P=Energy/time
Kinetic energy
1. All moving objects have kinetic energy
  1. E=0.5XmassXv^2 (speed)
2. kinetic energy depends on mass and speed
3. An object is 'elastic' if it regains its shape after being stretched/squashed
  1. When work is done on an elastic object it has elastic potential energy
Momentum
1. The greater the mass and velocity, the greater the momentum
  1. Momentum=mass x velocity
2. conservation of momentum=momentum stays the same after explosion/collision
Explosions
1. In an explosions 2 objects push apart with equal forces
  1. 1 positive 1 negative so momentum is 0
Impact forces
1. When vehicles collide the force of impact depends on: mass,velocity and duration
  1. If impact time is short forces are large
Car safety
1. Seat belts and airbags spread force across chest
2. Crumple zones increase impact time
3. We can use conservation of momentum to work out speed before impact

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