Momentum & Impulse

Momentum & Impulse

What is Momentum?

• 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​

What is 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​

Multiple Select

Which of the following variables are momentum dependent on?

• Mass

• Velocity

• Kinetic Energy

• Work

Multiple Select

Choose all of the following that have momentum

• A moving car on a highway

• A person sitting in a chair working on homework

• A person on their morning run

• Someone eating at a Chinese buffet

Momentum Equation

p = m x v

• Where....

  • p = momentum​

  • m = mass

  • v = velocity​

• Units: kg*m/s​

Multiple Choice

Which of the follwoing has the greatest momentum?

• Tortoise with a mass of 270 kg moving at a velocity of 0.5 m/s

• Hare with a mass of 2.7 kg moving at a velocity of 7 m/s

• Turtle with a mass of 91 kg moving at a velocity of 1.4 m/s

• Runner with a mass of 1.8 kg moving at a velocity of 6.7 m/s

Multiple Select

Which of the following situations is an example of a visible change in momentum?

• A hiker walks through a spider's web

• A volleyball hits a mosquito in the air

• A car drives over a pebble

• A baseball is hit by a bat

Multiple Choice

A skateboarder increases her speed for 2 m/s to 4 m/s. Her momentum....

• Increases

• Decreases

• Remains the same

• Goes to zero

Change in Momentum Equation

Change in p = m_fv_f - m_iv_i

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

Change in Momentum: Example

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?

How can we change 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

Impulse and Momentum: Example

​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?

Multiple Choice

The impulse necessary to cause a change of momentum of 20 kg*m/sec for a 5 kg object is....

• 5 N*sec

• 15 N*sec

• 20 N*sec

• 100 N*sec

Multiple Choice

The time required to stop a 200 kg wagon moving at 5 m/sec with a 40 N force is....

• 1 second

• 5 seconds

• 80 seconds

• 25 seconds

Momentum with Collisions

• Just like energy, momentum is CONSERVED

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

Elastic vs. Inelastic Collisions

• Elastic = Bounce off of each other after collision

• Inelastic = Stick together after collision

​

​Elastic: m₁v₁ + m₂v₂ = m₁v₁ + m₂v₂

​

Inelastic: ​m₁v₁ + m₂v₂ = mv

Momentum with Collisions: Example

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....

Momentum with Collisions: Example

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?