Energy and Momentum

1. Energy and Momentum Work Done Kinetic Energy Kinetic Energy Momentum Vehicle Safety Features

2. Work Work done is the transfer of energy Work done (J) = Force (N) x distance (m)

3. Work done against gravity • Work done against gravity = Gravitational Potential Energy (GPE) • Flying saucer Work done (J) = Force (N) x distance (m) So Upwards: GPE (J) = Weight (N) x height (m) (weight = mass x gravity)

4. Work done against friction • Rub hands together • Brakes in a car

6. 40 mph • She has been hit initially on the pelvis. Her pelvis has broken. She has been thrown approximately 28m from the car, and has fallen to the ground onto her arm initially, with her head hitting the road next, causing her skull to be fractured (hence the trickle of blood from the ear, and the blood in the hair). She has grazes on the side of her face (on her cheeks and temple) from where she has slid along the road.

7. 30 mph • She has been hit initially on the pelvis. Her pelvis is bruised. Having been hit initially in the pelvis she is thrown approximately 16 metres and falls onto her side, fracturing her arm (though it would not look distorted). She then hits her head, but not so hard as to concuss her.

8. Momentum momentum (kg m/s)= mass(kg) x velocity(m/s) • Air track

9. Conservation of momentum • In some crashes momentum is conserved • Eg, snooker balls colliding • So total momentum before = total momentum after Massb4 x velocityb4 = massafter x velocityafter

10. Vehicle safety features and momentum Egg and sheet

11. How crumple zones work force = change in momentum / time taken for the change Stays constant Can change