3.5 Momentum

• Newton's First Law of Motion

  An object will remain at rest or continue to move with constant velocity unless acted upon by another force
• Newton's Second Law of Motion

  $F=$$\frac{\Delta p}{\Delta t}=$$\frac{\Delta m\Delta v}{\Delta t}$

  p - momentum

  t - time

  m - mass

  v - velocity
• A special case of Newton's Second Law is F=ma as mass is constant
• Newton's Third Law of Motion

  When two objects interact, they exert equal and opposite forces on each other
• Characteristics of Newton's 3rd Law pair forces

  • Equal in magnitude
  • Opposite in direction
  • Forces are the same type (electrostatic, gravitational, contact, etc)
• Impulse is the area under a force-time graph; the product of force and the time for which the force acts; change in momentum
• Impulse = $\int_{ }^{ }F dt$
• When catching a ball, drawing your hands back increases the time taken for the ball to come to a stop, reducing the force applied on your hands
• $p=$$mv$

  p - momentum, $kgms^{-1}$

  m - mass

  v -velocity
• Momentum is a vector quantity as it is the product of velocity and mass
• Conservation of momentum

  For a system of interacting objects, the total momentum in a specified direction remains constant as long as no external forces act on the system
• An elastic collision is when there is no net loss of kinetic energy in the system as a result of the collision
• An inelastic collision is when there is a loss in kinetic energy but momentum is conserved - energy is transferred to thermal energy, sound energy and material deformation
• A perfectly inelastic collision is when the objects collide and they join to form one connected mass, because the maximum possible kinetic energy has been lost, but the final kinetic energy cannot be zero as momentum must be conserved