5.6 - Forces and motion

Cards (15)

  • Distance is how far an object moves.
  • Displacement includes both the distance an object moves, measured in a straight line from the start point to the finish point and the direction of that straight line.
  • The typical values of speed can include:
    • Walking ~ 1.5 m/s
    • Running ~ 3 m/s
    • Cycling ~ 6 m/s
  • Moving objects will always have a constantly changing speed. This also includes the speed of sound and wind. A typical value for the speed of sound in air is 330 m/s
  • The velocity of an object is its speed in a given direction.
  • Acceleration is the rate at which an object changes its velocity.
  • Newton's 1st Law:
    An object continues in its state of rest or constant speed in a straight line unless acted on by a resultant force. This means that when a vehicle travels at a steady speed the resistive forces balance the driving force.
  • Inertia is the tendency of an object to continue moving with a constant velocity until it experiences a net external force.
  • Newton's 2nd law:
    The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.
  • Newton's 3rd law:
    Two interacting objects exert equal and opposite forces on each other e.g. A book pushing on a table as the table pushes on the book. Keeping both objects in equilibrium
  • The thinking distance is the distance the vehicle travels during the driver's reaction time
  • The braking distance is the distance the vehicle travels whilst the driver is braking
  • The stopping distance is the thinking distance + the braking distance
  • A vehicle's brakes transforms the kinetic energy of the vehicle to thermal energy using friction. Brakes will get very hot so need to dissipate this thermal energy efficiently to the surroundings. A large deceleration may lead to brakes overheating and/or loss of control
  • The braking distance of a vehicle can be affected by:
    • Adverse road
    • Weather conditions
    • Poor condition of the vehicle