Topic 2 - Newton's Laws

• What is a force?

  A push or pull acting on an object due to an interaction with another object.
• Define resultant force.

  The sum of all the individual forces acting on an object (taking directions into account).
• How is resultant force calculated?

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

  If the resultant force on a stationary object is zero, the object will remain at rest.
• State Newton's first law for a moving object.

  If the resultant force an a moving object is zero, the object will remain at constant velocity (same speed in same direction).
• If an object changes direction but remains at a constant speed, is there a resultant force?

  Yes; since there is a change in direction, there is a change in velocity and so there must be a resultant force.
• What happens if there is zero resultant force?

  The object will remain stationary or continue to move with constant speed and direction.
• What is inertia?

  The tendency of an object to continue in its state of rest or uniform motion.
• State the defining equation for Newton's Second Law.

  Resultant force = Mass × Acceleration

  F = ma
• State Newton's Second Law in words.

  An object's acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass.
• What is 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 (derived from F=ma)
• State Newton's Third Law.

  Whenever two objects interact, the forces that they exert on each other are always equal and opposite.
• What is weight?

  The force that acts on an object due to gravity and the object's mass.
• What quantities does weight depend on?

  Weight = mass × gravitational field strength

  • The object's mass
  • The gravitational field strength at the given position in the field
• What is the unit used for weight?

  The Newton (N).
• What is the gravitational field strength on the surface of Earth?

  10 N/kg
• What is the approximate weight of a 1kg object on the surface of Earth?

  10 Newtons
• When does a falling object reach terminal velocity?

  • When the upwards forces (air resistance) and the downwards forces (weight) are equal to each other.
  • No resultant force, so constant speed.
• What happens to the magnitude of air resistance on a falling object when the velocity increases?

  As velocity increases, the force of air resistance on the object will also increase.