Summary CIE A Level Chapter 3 - Dynamics

Dynamics
 Mass = quantity of matter; measure of the inertia of an object to changes in velocity

Newton’s First Law

 An object remains at rest or travelling at a constant velocity unless a resultant force is
applied


Newton’s Second Law

dp
 F= is the actual form of NL2 where p is momentum, and momentum is equal to the
dt
product of mass and velocity
 F=ma is only true where the mass is constant
 In words, we can write either resultant force is equal to the rate of change of momentum or
resultant force on an object is proportional to the mass of the object and its acceleration in
the same direction as the force
 This law leads to NL1


Newton’s Third Law

 Force of body A on body B is equal in magnitude and opposite in direction to the force
exerted by body B on A
 These forces are of the same kind


Momentum and Newton’s Laws Summarised

 Newton’s Second Law or NL2 can be used to state F=ma and solve in various scenarios
 Note the definition of force is rate of change of momentum
 Weight = the effect of a gravitational field on a mass
 Weight = mass x acceleration of free fall



Non-Uniform Motion

 Drag increases as speed increases
 Hence as an object is falling, the drag will increase until it is equal to the object’s weight
 Hence the object will be in equilibrium, moving at a constant terminal velocity