Physics OCR Chapter 7 (Laws of Motion and Momentum)

Newton’s First Law: An object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force

Newton’s Third Law: When two object interact, they exert equal and opposite forces on each other

All types of interaction can be explained by four fundamental forces: gravitational, electromagnetic, strong nuclear and weak nuclear

— The two nuclear forces have short range, very little impact on the day to day
— Gravational force, why we stay on earth
— When you push your hands together the contact force you feel is due to the electrostatic repulsion between the electron clouds in your hands

Momentum
Momentum (p) = Mass (m) x Velcoity (v)
Kg m s-1 =. Kg x. m/s
Momentum is a vector quantity

Conservation of momentum
In a collision objects transfer both KE and Momentum
In a closed system the total momentum doesn’t change, therefore, p before = p after

Elastic or Inelastic Collisions

Elastic = momentum conserved, total energy conserved, total KE conserved
Inelastic = momentum conserved, total energy conserved, total KE not conserved

Newton’s Second Law: The net resultant force acting on an object is directly proportional to the rate of change of its momentum and is in the same direction

Therefore: net resultant force ∝ rate of change of Momentum

F ∝ Δp / Δt    →    F = K Δp /Δt  

K = 1

∴ Newton's 2nd law can be written as 

 F =  Δp /Δt  

Impulse

 F = Δp /Δt   can be rearranged to  Δp = F x Δt  

The impulse of a force is defined as product of force and the time for which this force acts

∴      impulse of a force = change in momentum

Force-Time Graphs

Area under a force time graph always = change in momentum