Force and Motion

• Force: The action of one body on a second body.
• Unbalanced forces cause changes in speed, shape, or direction.
• 1 N = force required to give a mass of 1 kg an acceleration of 1 m/s2
• Air Resistance: a form of friction/drag caused when an object moves through air
• Friction: The force that acts when 2 surfaces rub over each other
• Drag: Friction that acts on an object moving through a fluid(liquid/gas)
• Solid friction: The resistance to motion caused when 2 surfaces are in contact
• Unbalanced forces result in change in acceleration
• Balanced forces result in constant speed
• Gravity: The force of attraction that exists between any two objects with mass
• On Earth, the force of gravity is 9.8 N
• Weight: The gravitational force acting on an object that has mass
• w = mg
• g = w/m
• Terminal velocity: The greatest speed an object can reach while falling through a fluid
• At terminal velocity, weight = drag, thus, forces acting on the object are balanced.
• Any object moving along a circular path is changing direction, which requires force
• By moving in a circle, the object’s velocity is constantly changing due to constant change in direction (even if speed = constant)
• Acceleration=change in velocity/time taken
• Resultant force=mv-mu/t
• momentum = mass x velocity
• impulse = mv - mu; or change in momentum
• Impulse = F x t
• The effect of force depends on magnitude and time.
• Principle of conservation of momentum states that total momentum before = total momentum after
• Acceleration depends on :

  1. Mass: more mass, smaller acceleration.
  2. Force: more force, more acceleration.
• The size of the resultant force needed to make an object travel in a circle depends on:

  • Mass of the object: more the mass, more the resultant force.
  • Speed of the object: faster the speed, more the resultant force.
  • Radius of the circle: smaller the radius, more the resultant force.