1.1. To understand what momentum isTo understand what momentum is

2.2. To understand conservation of momentum To understand conservation of momentum and to be able to complete related and to be able to complete related calculationscalculations

3.3. To understand different types of collision, to To understand different types of collision, to be able to complete related calculations and be able to complete related calculations and to be able to classify a collision as either to be able to classify a collision as either elastic or inelasticelastic or inelastic

Book Reference : Pages 4-17Book Reference : Pages 4-17

Which is more effective at demolishing a wall?Which is more effective at demolishing a wall?

A 1kg metal ball moving at 50msA 1kg metal ball moving at 50ms-1-1

Or a 1000kg ball moving at 1msOr a 1000kg ball moving at 1ms-1-1

Newton realised that what happens to a moving Newton realised that what happens to a moving objects involved in a collision depends upon two objects involved in a collision depends upon two things : things :

•Mass of the objectMass of the object

•Velocity of the object Velocity of the object

Newton used the concept of momentum to Newton used the concept of momentum to explain the results of collisionsexplain the results of collisions

Momentum Momentum = mass x velocity= mass x velocity

p p = m v= m v

Units :Units :

p (kg msp (kg ms-1-1) ) = m (kg) x (ms= m (kg) x (ms-1-1))

Note since velocity is a Note since velocity is a vectorvector quantity, (both quantity, (both magnitude and direction) then magnitude and direction) then momentummomentum is also is also a a vectorvector quantity quantity

When objects collide, assuming that there are no When objects collide, assuming that there are no external forces, then momentum is always external forces, then momentum is always conserved.... Definition :conserved.... Definition :

When two or more objects interact, the total When two or more objects interact, the total momentum remains constant provided that momentum remains constant provided that there is no external resultant forcethere is no external resultant force

Mass 75 kgVelocity 4 ms-1

Mass 50 kgVelocity 0 ms-1

Mass 125 kgVelocity ??? ms-1

When objects hit each other the resulting When objects hit each other the resulting collision can be considered to be either elastic or collision can be considered to be either elastic or inelastic. Momentum and inelastic. Momentum and totaltotal energy are always energy are always conserved in both cases. conserved in both cases.

Elastic :Elastic : momentum conserved, kinetic momentum conserved, kinetic energy conserved, total energy energy conserved, total energy conservedconserved

Inelastic :Inelastic : momentum conserved, kinetic momentum conserved, kinetic energy energy NOTNOT conserved, total energy conserved, total energy conservedconserved

In an Inelastic collision some of the kinetic energy is In an Inelastic collision some of the kinetic energy is converted to other forms of energy (often heat & Sound)converted to other forms of energy (often heat & Sound)

Is the following collision elastic or inelastic?Is the following collision elastic or inelastic?

A toy lorry of mass 2kg is travelling at 3msA toy lorry of mass 2kg is travelling at 3ms-1-1 and crashes into a smaller a toy car with a and crashes into a smaller a toy car with a mass of 800g which is travelling at 2 msmass of 800g which is travelling at 2 ms-1-1 in the in the same direction as the lorry. The velocity of the same direction as the lorry. The velocity of the lorry after the collision is 2.6 mslorry after the collision is 2.6 ms-1-1. What is the . What is the velocity of the car after the collision and is the velocity of the car after the collision and is the crash elastic or inelastic? crash elastic or inelastic?

Mass 2 kgVelocity 3 ms-1

Mass 800 gVelocity 2 ms-1

Mass 800gVelocity ? ms-1

Mass 2 kgVelocity 2.6 ms-1

Lorry Momentum = 2 x 3Lorry Momentum = 6 kgms-1

Car Momentum = 0.8 x 2Car Momentum = 1.6 kgms-1

Total momentum before = 7.6 kgms-1

Total momentum after= 7.6 kgms-1

Lorry Momentum = 2 x 2.6Lorry Momentum = 5.2 kgms-1

Car Momentum = Total - LorryCar Momentum = 7.6 – 5.2Car Momentum = 2.4 kgms-1

Car Momentum = 0.8v

v = 2.4 / 0.8 = 3 ms-1

Mass 2 kgVelocity 3 ms-1

Mass 800 gVelocity 2 ms-1

Mass 800gVelocity 3 ms-1

Mass 2 kgVelocity 2.6 ms-1

Lorry Ek = ½ x 2 x (3)2

Lorry Ek = 9J

Car Ek = ½ x 0.8 x (2)2

Car Ek = 1.6J

Total Ek before = 10.6J

Lorry Ek = ½ x 2 x (2.6)2

Lorry Ek = 6.76J

Car Ek = ½ x 0.8 x (3)2

Car Ek = 3.6J

Total Ek after= 10.36J

Total Ek before Total Ek afterInelastic Collision

Where is the energy likely to have gone?

Two trolleys on an air track are fitted with Two trolleys on an air track are fitted with repelling magnets. The masses are 0.1kg and repelling magnets. The masses are 0.1kg and 0.15kg respectively. When they are released the 0.15kg respectively. When they are released the lighter trolley moves to the left at 0.24mslighter trolley moves to the left at 0.24ms-1-1. What . What is the velocity of the heavier trolleyis the velocity of the heavier trolley

A ball of 0.6kg moving at 5msA ball of 0.6kg moving at 5ms-1-1 collides with a collides with a larger stationary ball of mass 2kg. The smaller ball larger stationary ball of mass 2kg. The smaller ball rebounds in the opposite direction at 2.4msrebounds in the opposite direction at 2.4ms-1-1

Calculate the velocity of the larger ballCalculate the velocity of the larger ball

Is the Collision elastic or inelastic. Explain your Is the Collision elastic or inelastic. Explain your answeranswer