physics unit 3

key points and formulas from AQA PHYSICS UNIT 3 :)

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  • Created by: SCOTT
  • Created on: 04-05-10 19:50

turning forces- moments

  • The turning effect of a force is called the moment.
  • a moment can increased by increasing the size of the force and increasing the distance from the pivot/centre point
  • moments are measure in newton metres: Nm


moment = force x perpendicular distance from where the force is being applied.

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turning forces-centre of mass

  • the centre of mass of an object is where the mass is thought to be most concentrated.
  • an object that is being suspended will always return to a point where its centre of mass is directly below the point of suspension. the object is then at equilibrium meaning there is no turning force.
  • the centre of mass for a symmetrical object run along it's lines of symmetry.
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turning forces- balancing moments

for an object to be in equilibrium:

the sum of all the clockwise moments about any point


the sum of all anticlockwise moments about that point.


(force1 x distance 1) = (force 2 x distance 2)

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turning forces-stability

to increase stability:

  • increasing the width of the objects base
  • lowering the centre of mass

an object will topple over if its line of action of its weight acts outside its base

(imagine a line along the centre of mass is acting straight down and this line goes outside of the base of an objectas the object tilts.)

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turning forces-circular motion

when an object moves around a circle at a constant speed:

  • the object accelerates continuously towards the centre of the circle.
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