Forces

• What is a scalar quantity?

  Only has a size (magnitude)
• What is a vector quantity?

  Has both a size and direction
• What is a force?

  A force is a push or pull that can cause an object to move, stop, or change direction
• What quantity is a force?

  Vector
• What is a contact force?

  When objects physically touch
• 4 contact forces

  1. Friction
  2. Air resistance
  3. Normal contact force
  4. Tension
• What is a non contact force

  When objects are physically separated
• 3 non contact forces

  1. Magnetic force
  2. Electrostatic force
  3. Gravitational force
• How to work out resultant force

  Same direction: Add forces together

  Diff direction: Difference between forces
• Force acting on an object due to gravity

  Weight
• Elastic deformation

  Object can go back to original shape when forces are removed
• Inelastic deformation

  Object cannot go back to its original shape after forces are removed
• What quantity is distance

  Scalar
• What quantity is displacement

  Vector
• What quantity is speed

  Scalar
• What quantity is velocity

  vector
• Typical speeds for someone walking running and cycling

  Walking: 1.5m/s

  Running: 3m/s

  Cycling: 6m/s
• Typical speeds for cars and trains

  Car: 13-30m/s

  Train: 50m/s
• Speed for sound travelling in air

  330m/s
• What is acceleration

  Change in velocity of an object per second
• Unit of acceleration

  m/s
• How to reduce drag on an object

  Streamlining
• Newtons first law

  Says that the velocity, speed, and/or direction of an object will only change if a resultant force is acting on it
• Newtons second law

  Says that the acceleration of an object is

  1. proportional to the resultant force on the object
  2. Inversely proportional to the mass of the object
• Newtons third law

  Says that whenever 2 objects interact with each other, they exert equal and opposite forces on each other
• Resultant force on stationary object

  0
• Resultant force on object moving at a steady speed in a straight line


  0
• What does an object experience if the resultant force is not 0

  Change in velocity
• Stopping distance

  Distance a vehicle travels to safely come to a stop
• Thinking distance

  Distance vehicle travels during drivers reaction time
• Braking distance


  Distance vehicle travels once breaks have been applied
• Relationship between stopping distance, breaking distance and thinking distance

  Stopping distance = thinking distance = breaking distance
• Law of conservation of momentum

  In a closed system, the total momentum before an event is equal to the total momentum after it