Momentum (Edexcel GCSE Physics: Combined Science)

Higher Tier Only

• A moving object has momentum which 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)

• This means that an object at rest (i.e 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

• Since velocity is a vector this means that the momentum of an object also depends on its direction of travel
• This means that momentum can be either positive or negative
  • If an object travelling to the right has positive momentum, an object travelling in the opposite direction (to the left) will have negative momentum

The tennis ball's momentum is negative when it moves in the opposite direction to which it initially was travelling in

• Therefore, the momentum of an object will change if:
  • The object accelerates (speeds up) or decelerates (slows down)
  • Changes direction
  • Its mass changes

Higher Tier Only

• Examples of momentum in an event are collisions
• Objects will either:
  • Collide and move in opposite directions - this is an elastic colision
  • Collide and move in the same direction together - this is an inelastic collision

• When the objects move in opposite directions:
  • Each object will have a different velocity depending on its mass and initial momentum of the system

• When the objects move in the same direction together:
  • They will have a combined mass and velocity

• Momentum is always conserved in a collision

The difference between elastic and inelastic collisions