Motion Forces - Topic 1

• Newton's 1st Law

  A resultant force is required to change the motion of an object
• Newton's 2nd Law

  • Non-zero resultant force acts on an object then it will cause the object to accelerate
  • The size of the resultant force is directly proportional to the acceleration it causes and inversely proportional to the object's mass
• Newton's 3rd Law

  When two objects interact, the forces they exert on each other are equal and opposite
• Balanced forces

  • One object
  • Two or more forces
• Action-reaction

  • Two objects
  • One force
• Resultant Force


  The overall force of the forces acting on an object
• Centripetal Force 


  An object, moving a circle has changing velocity, even though it's speed remains the same. The resultant force that causes the change in the direction is called the centripetal force and cats towards the center of the circle. Velocity continuously changing because of the change in direction and the continuous change in acceleration is due to the velocity changing.
• How does increasing the radius of orbit affect the centripetal force?

  It decreases the centripetal force required to maintain the same speed.
• Mass and Weight

  • Mass - the amount of matter in an object.
  • Weight - The force pulling an object downwards. It depends on mass and the gravitational field strength of the object.
• Inertia 


  The tendency for the motion of an object to remain unchanged.
• Inertial Mass 


  How difficult it is to change an objects velocity.
• Conservation Of Momentum

  In a closed system :

  Total momentum before an event = Total momentum after an event

  Momentum conserved only in collisions and explosions.
• How do Airbags and Seat belts reduce collision?

  They increase collision time, which increases the rate of change of momentum.
• An investigation to show momentum is conserved when two trolleys collide

  • Measure the mass of the trolleys
  • Determine speed of 1st trolley then the 2nd trolley
  • Use light gates further down runways
  • Trolleys stick together
  • Measure momentum
• Thinking Distance 


  The distance the car travels while the driver reacts to the problem.
• Braking Distance


  The distance the car travels while the vehicle brakes.
• Factors that increase braking distance

  • Worn tires
  • Worn brakes
  • Slippery roads
  • Vehicle mass
  • Speed of vehicle
• Factors increasing reaction time (needs more time)

  • Illness
  • Tiredness
  • Drugs and alcohol
  • Mobile phones
  • Other distractions
• Experiment Variables: Independent and Control

  • Independent - height of ramp
  • Control - same card and trolley
• Method to calculate average speed?

  • Measure distance using meter ruler or trundle wheel
  • Record time using stop watch
  • Workout average speed = distance/ time
• Newtons 3rd Law and Conservation of Momentum

  Newtons 3rd Law states when two objects collide they exert equal and opposite forces on each other and their velocities change. However total momentum of the system remains the same before and after collisions. If one object gains momentum, the other must loose the same amount of momentum to stay the same.