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Science

Forces and motion

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Acceleration is caused by a force, eg gravity or friction, acting on a moving object. The relationship between force, mass and acceleration is expressed in the equation 'force = mass x acceleration'.

The stopping distance of a car depends on two factors - thinking distance and braking distance. Under normal driving conditions, the thinking and braking distance depend on the speed of the car.

Forces, mass and acceleration

When an object accelerates it does so because an extra force is acting on it. For example:

  • Gravity causes a falling apple to speed up as it falls.
  • Air resistance causes a parachutist to slow down just after opening the parachute.
  • The brake pads on a bike cause extra friction, which slows the bike down.

The relationship between force, mass and acceleration

For the same mass:

  • more force causes more acceleration
  • less force causes less acceleration
Mass increases as force and acceleration increase

For the same force:

  • more mass causes less acceleration
  • less mass causes more acceleration
force decreases as acceleration and mass increase

For the same acceleration:

  • more mass needs more force
  • less mass needs less force
Acceleration increases as force and mass increase.

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