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I/GCSE Physics - Moments and Circular Motion

Centre of mass, balanced moments, stability, centripetal force

· igcse physics,gcse physics,Moments,Circular motion,Centre of mass

Turning effects

  • Moment (Nm) = force (N) x perpendicular distance from pivot (m).
  • The moment can be increased by increasing the size of the force or using a longer instrument.
  • Force applied by a person is called effort.
  • The closer to the pivot you are,  the harder it will be to lift the load.

Centre of Mass

  • Centre of mass = the point of an object where it’s mass is thought to be concentrated.
  • In symmetrical objects, the centre of mass is along the lines of symmetry or where the lines of symmetry meet.
  • A hanging object rests with it’s centre of mass directly below the point of suspension.
  • This is called being in equilibrium.
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Balanced moments

  • For objects in equilibrium, the total clockwise moment is equal to the total anticlockwise moment.
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  • To work out this weight, we do 0.3 x 2 = 0.6
  • Then, 0.6/0.4 = 1.5N.
  • You can also use this to work out unknown distances.

Stability

  • Stable objects usually have a wide base and a very low centre of mass.
  • When the line of action of weight lies outside the base of an object, it will topple over.
  • When the line of action of weight lies inside the base of an object, it shouldn’t topple over.
  • Buses and coaches have to take special tests which make sure they do not topple over too easily.

Circular motion

For any object moving in a circle at constant speed:

  • Its velocity is directed along a tangent to the circle of direction.
  • The velocity constantly changes direction as it moves around the circle.
  • The change of velocity is towards the centre of the circle.
  • Therefore the object is constantly accelerating towards the centre of the circle.
  • The force that acts towards the centre of the circle is called the centripetal force.
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Make sure you understand the concepts well as these are very important in I/GCSE Physics! 👨‍🏫

Centripetal force

Factors that increase centripetal force:

  • Decreased radius of the circle e.g. a ball being swung around in a circle on a SHORT piece of string.
  • Increased mass of object e.g. a LARGER ball being swung around in a circle on a short piece of string.
  • Basically, the larger and further away the object is, the larger the centripetal force will be.
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Gravitational forces

Gravity is:

  • An attractive force.
  • Gets bigger with the mass of each object.
  • Gets smaller when the objects get further away from each other.
  • As an object leaves the Earth’s atmosphere, the gravitational force acting on it due to the Earth decreases and the gravitational force acting on it due to the moon increases.

References:

http://hyperphysics.phy-astr.gsu.edu/hbase/cm.html

https://commons.wikimedia.org/wiki/File:Circular_motion_velocity_and_acceleration.svg

https://en.wikipedia.org/wiki/Centripetal_force

This is the end of the topic!

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Drafted by Cherry (Chemistry)

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