Newtons Laws

• Force


  A push or pull acting on an object due to an interaction with another object
• Resultant force


  The sum of all the individual forces acting on an object (taking directions into account)
• How to calculate resultant force

  Adding together the vector arrows of all the individual forces
• Newton's first law for a stationary object

  If the forces on a mass are balanced (no resultant force) then if it is in rest, it stays in rest
• Newton's first law for a moving object:

  If the forces on a mass are balanced (no resultant force) then if it is moving, it keeps moving at a constant speed in a straight line
• If an object changes direction but remains at a constant speed, there is a resultant force
• If there is zero resultant force, the object will remain stationary or continue to move with constant speed and direction
• Inertia


  The tendency of an object to continue in its state of rest or uniform motion
• Newton's Second Law (equation)

  Resultant force = Mass x Acceleration (F = ma)
• Newton's Second Law (words)

  The rate of change of momentum is proportional to the (resultant) force applied and takes place in the direction of the (resultant) force
• Inertial mass


  A measure of how difficult it is to change a given object's velocity, the ratio of force over acceleration (m = F/a)
• Newton's Third Law:

  In an interaction between two bodies A and B, the force exerted by body A to body B is equal and opposite to the force exerted by body B to body A
• Weight

  The force that acts on an object due to gravity and the object's mass
• What weight depends on

  • The object's mass, the gravitational field strength at the given position in the field (Weight = mass x gravitational field strength)
• The unit used for weight is the Newton (N)
• The gravitational field strength on the surface of Earth is 10 N/kg
• The approximate weight of a 1kg object on the surface of Earth is 10 Newtons
• When a falling object reaches terminal velocity

  When the upwards forces (air resistance) and the downwards forces (weight) are equal to each other, resulting in no resultant force and constant speed
• As velocity increases

  The force of air resistance on the object will also increase