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
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
