Definition - strictly speaking it should be Linear Momentum momentum (p) = mass (m) x velocity (v) p = m v Units of momentum will be kgms-1. Momentum is a vector quantity.

E.g. calculate the momentum and Ek of the following objects a) a fly of mass 10g hitting an aircraft window at 880kmh-1 and b) a tank of mass 15 tonne travelling at 30kmh-1. First convert the velocities to ms-1 880kmh-1 = 880 x 1000 / 60 x60 = 244ms-1 30kmh-1 = 30 x1000 / 60 x 60 = 8.33ms-1

E.g. calculate the momentum and Ek of the following objects a) a fly of mass 10g hitting an aircraft window at 880kmh-1 and b) a tank of mass 15 tonne travelling at 30kmh-1. 880kmh-1 = 880 x 1000 / 60 x60 = 244ms-1 30kmh-1 = 30 x1000 / 60 x 60 = 8.33ms-1

The principle of conservation of momentum The total linear momentum of any closed system of interacting particles in any particular direction is constant. This is best understood as the fact that the total momentum before a collision is equal to the total momentum after the collision. It applies also to explosions.

Questions: 1 An astronaut of mass 80kg who is at rest in deep space throws a spanner of mass 0.5kg at a velocity of 2ms-1. Describe the velocity of the astronaut. 2 An aircraft is travelling at 700 kmh-1 and explodes into 4 equal pieces which miraculously fly up, down, forwards and backwards. The forward piece travels at 750kmh-1 in the horizontal, what is the horizontal velocity of the piece going backwards? 3 A bullet of mass 10g hits a wooden block of mass 1kg and sticks into it. The block and bullet move off with an initial velocity of 2ms-1. What was the inital velocity of the bullet?

1 An astronaut of mass 80kg who is at rest in deep space throws a spanner of mass 0.5kg at a velocity of 2ms-1.

2 An aircraft is travelling at 700 kmh-1 and explodes into 4 equal pieces which miraculously fly up, down, forwards and backwards. The forward piece travels at 750kmh-1 in the horizontal, what is the horizontal velocity of the piece going backwards?

3 A bullet of mass 10g hits a wooden block of mass 1kg and sticks into it. The block and bullet move off with an initial velocity of 2ms-1. What was the inital velocity of the bullet?

An experiment to confirm the principle of conservation of momentum Use the linear airtrack, two cars, two light gates and two timers. Timers Light gates separated by a distance Card of length x

Timers Light gates separated by a distance Card of length x The first light gate is used to measure the initial speed of the first car while the other one is stationary. They then collide and stick together (because there is a pin on one and a piece of cork on the other). The two, now travelling more slowly pass through the second light gate. This allows us to measure the final speed. List the measurements that you would need to make and explain how you would use these`measurements to show that momentum had been conserved.

Solution Measurements: Masses of each car Length of card which breaks the light beam Time taken for the card to break the beam in each case Then: Calculate the initial (u) and final (v) velocities by dividing the length of the card by the time for each beam to be broken. Find the initial momentum pi mass of first car x u Find the final momentum mass of (first + second) car x v If the momentum is conserved, the two numbers should agree within acceptable experimental uncertainty. Why did you use an airtrack to do this?

The end