chap 3 forces and movement

• ABS = Anti-lock Braking System


  reduce the chance of a skid occuring
• Thinking distance / Reaction time : Before we react to a danger our brain takes time to think (reaction time). The distance travelled during this time is the thinking distance.


  Thinking distance is the distance a car travels after the driver has seen a danger and before the driver applies the brakes.
• Thinking distance depends on-

  1. Tiredness of the driver
  2. Use of alcohol or drugs
  3. Poor visibility
  4. Speed of car
• Breaking distance depends on-

  1. Road condition(icy or wet)
  2. tyres condition(not enough to grip the road surface)
  3. Speed of car
  4. condition of the brakes
• Stopping distance= thinking distance+ breaking distance
• Weight(def) : The weight of an object is the force that acts on it because of gravity. The weight of an object depends on its mass and the strength of gravity.


  The weight is the term we use for the earth's gravitational force on an object.
• weight = mass x gravitational field strength


  w = mg
• 1. If location change but mass doesn't change, weight will change.
  2. If location doesn't change but two objects have different mass, larger mass will have greater weight.
  3. Gravitational field strength depends on the mass of the planet. Greater mass planet has greater value of "g"
• g

  • gravitational field strength
  • acceleration due to gravity(no air resistance)


  (acceleration due to gravity= acceleration of free fall)
• The difference in air is due to air resistance having a greater effect on light bodies than on heavy bodies.
• Acceleration of free fall

  Uniform acceleration of bodies falling freely under the force of gravity when air resistance is negligible
• Acceleration of free fall (g)

  Varies slightly from one place on the earth's surface to another due to variations in the earth's gravitational pull, but the variation is less than 1%
• On average, the acceleration of free fall (g) is about 9.8m/s2, or near enough 10m/s2
• Moving away from the earth and out into space

  The acceleration of free fall (g) decreases
• Velocity of a free-falling body

  Increases by about 10m/s every second