Physics 2.3

Physics 2.3

1. Energy and work

   • When a force moves an object, work is done
   • Energy transferred= work done
     • Work=force x distance
   • Work done to overcome friction is transferred to heat energy

2. Gravitational potential energy

   • The gpe of an object depends on its weight and how far it moves vertically
   • change in gravitational potential= massXgravitational field strengthXchange in height
   • Power is the rate of transfer of energy
     • P=Energy/time

3. Kinetic energy

   • All moving objects have kinetic energy
     • E=0.5XmassXv^2 (speed)
   • kinetic energy depends on mass and speed
   • An object is 'elastic' if it regains its shape after being stretched/squashed
     • When work is done on an elastic object it has elastic potential energy

4. Momentum

   • The greater the mass and velocity, the greater the momentum
     • Momentum=mass x velocity
   • conservation of momentum=momentum stays the same after explosion/collision

5. Explosions

   • In an explosions 2 objects push apart with equal forces
     • 1 positive 1 negative so momentum is 0

6. Impact forces

   • When vehicles collide the force of impact depends on: mass,velocity and duration
     • If impact time is short forces are large

7. Car safety

   • Seat belts and airbags spread force across chest
   • Crumple zones increase impact time
   • We can use conservation of momentum to work out speed before impact