Momentum & Impulse

• Momentum is commonly used in sports

  • ​A football player that has momentum is MOVING, and will take effort to stop​

• If an object is moving, it has momentum​

• Defined as "mass in motion"

• All objects have mass

  • Therefore, if an object is moving, it has momentum​

• Momentum depends on two variables:

  • How much stuff is moving (aka, how much mass it has)

  • How fast it's going​

p = m x v

• Where....

  • p = momentum​

  • m = mass

  • v = velocity​

• Units: kg*m/s​

Change in p = m_fv_f - m_iv_i

• If an object can HAVE momentum, it can change its momentum​

A 5 kg ping pong moves at a velocity of 10 m/s. The ball is struck by a paddle, causing it to rebound in the opposite direction at a speed of 20 m/s. What is the change in the ball's momentum?

• By applying a force over a period of time can change the momentum of an object​​

• This is called Impulse = change in momentum​

​Impulse = Force x Time

Since Impulse = change in momentum

​F x t = m_fv_f - m_iv_i

​A car is traveling at 1000 m/sec and is stopped at a stop light at an impulse of 100 N*sec. What is the mass of the car?

• Just like energy, momentum is CONSERVED

• Meaning, the momentum before the collision equals the momentum after the collision​

• Elastic = Bounce off of each other after collision

• Inelastic = Stick together after collision

​

​Elastic: m₁v₁ + m₂v₂ = m₁v₁ + m₂v₂

​

Inelastic: ​m₁v₁ + m₂v₂ = mv

During a football game, a 90 kg running back moving east is tackled by a 110 kg defensive lineman running west at 5 m/sec. Both players move east at 1.5 m/sec after the tackle is made. Before he is tackled, the running back is moving with a speed of about....

A large fish weighing 3 kg is in motion at 2 m/s when it encounters a smaller fish that weighs 1 kg that is at rest. The large fish swallows the smaller fish and continues in motion at a reduced speed. What is the speed of the large fish (and the smaller fish) after the collision?