Linear Momentum (CIE A Level Physics)

• When an object with mass is in motion and therefore has a velocity, the object also has momentum
• Linear momentum is the momentum of an object that is moving in only one dimension
• The linear momentum of an object remains constant unless the system is acted upon by an external resultant force

• Momentum is defined as the product of mass and velocity

• Where:
  • = momentum, measured in kg m s⁻¹ 
  • - mass, measured in kg
  • = velocity, measured in m s⁻¹ 

• Momentum is a vector quantity with both magnitude and direction
  • The initial direction of motion is usually assigned the positive direction

When the ball is travelling in the opposite direction, its velocity is negative. Since momentum = mass × velocity, its momentum is also negative

• Both the tennis ball and the brick have the same momentum
• Even though the brick is much heavier than the ball, the ball is travelling much faster than the brick
• This means that on impact, they would both exert a similar force (depending on the time it takes for each to come to rest)