Momentum

• Momentum is defined by the equation: p = mv

  Where:

  • p = momentum in kilogram metre per second (kg m/s)
  • m = mass in kilograms (kg)
  • v = velocity in metres per second (m/s)

  An object at rest (v = 0) has no momentum

  Momentum keeps an object moving in the same direction, making it difficult to change the direction of an object with a large momentum

  The momentum of an object depends on its direction of travel, which can be positive or negative
• The momentum of an object will change if:

  • The object accelerates (speeds up) or decelerates (slows down)
  • Changes direction
  • Its mass changes
• Conservation of Momentum:

  • In a closed system, the total momentum before an event is equal to the total momentum after the event
  • Momentum is always conserved over time
  • Momentum is a vector quantity, so a system of objects moving in opposite directions at the same speed will have an overall momentum of 0 since they will cancel out
• Newton's Third Law:

  • Whenever two bodies interact, the forces they exert on each other are equal and opposite
  • All forces arise in pairs
  • Force pairs are of the same type
  • Newton's third law explains the forces that enable someone to walk
• Force & Momentum:

  • When a force acts on an object that is moving, the object will accelerate or decelerate
  • Force is the rate of change in momentum
  • Force and momentum are vectors, so they can be either positive or negative values
• Newton's first law of motion:

  • Objects will remain at rest, or move with a constant velocity unless acted on by a resultant force
• Newton's third law of motion:

  • Whenever two bodies interact, the forces they exert on each other are equal and opposite
• Newton's third law in collisions:

  • When one object exerts a force on another object, the second object will exert an equal force on the first object in the opposite direction
  • In collisions, both objects will react, generally causing one object to speed up (gain momentum) and the other object to slow down (lose momentum)
• Safety features in vehicles:

  • Vehicle safety features are designed to absorb energy upon an impact by changing shape
  • Main vehicle safety features are crumple zones, seat belts, and airbags
  • For a given force upon impact, these features absorb the energy and increase the time over which the force takes place, reducing the risk of injury
• Seat belts:

  • Designed to stop a passenger from colliding with the interior of a vehicle by keeping them fixed to their seat in an abrupt stop
  • They stretch slightly to increase the time for the passenger’s momentum to reach zero and reduce the force on them in a collision
• Airbags:

  • Deployed at the front on the dashboard and steering wheel when a collision occurs
  • Act as a soft cushion to prevent injury on the passenger when they are thrown forward upon impact
• Crumple zones:

  • Designed into the exterior of vehicles to crush or crumple in a controlled way in a collision
  • Increase the time over which the vehicle comes to rest, lowering the impact force on the passengers
• Crash mats:

  • Used in gymnasiums to reduce the risk of injury for falls in gymnastics and climbing
  • Offer shock absorption of the force created by the person landing on the mat
  • Increase the contact time over which their momentum is reduced, creating a smaller impact force and a lower chance of injury
• In a collision, if the total initial momentum is equal to the total final momentum, it is called an elastic collision.
• Momentum can be transferred between objects through collisions or forces acting on them.
• The momentum of an object is the product of its mass and velocity.