P3 1 Turning Forces

Key points of P3 1 - Turning Forces.

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P3 1.1 Moments

  • The moment of a force F about a pivot is F x d, where d is the perpenidicular distance from the pivot to the line of action of the force.
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P3 1.2 Centre Of Mass

  • The centre of mass of an object is the point where its mass is thought to be concentrated.
  • When a suspended object is in equilibrium, its centre of mass id directly beneath the point of suspension.
  • The centre of mass of a symmetrical object is along the axis of symmetry.
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P3 1.3 Moments In Balance

  • For an object in equilibrium, the sum of the anticlockwise moments about any point = the sums of the clockwise moments about that point.
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P3 1.4 Stability

  • The stability of an object is increased by making its base as wide as possible and its centre of mass as low as possible.
  • An object will tend to topple over if the line of action of its weight is outside its base.
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P3 1.5 Circular Motion

  • For an object moving in a circle at a constant speed,
    • the object accelerates continuously towards the centre of the circle,
    • the centripetal force needed increases,
      • as the mass or the speed of the object increases
      • as the radius of the circle decreases
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P3 1.6 Gravitational Attraction

  • The force of gravity between two objects
    • is an attractive force,
    • is bigger the greater the mass of each object is,
    • is the smaller the greater the distance between the two objects is.
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P3 1.7 Planetary Orbits

  • To stay in orbit at a particular distance, a small body must move at a particular speed around the larger body.
  • The larger an orbit is, the longer the orbiting body takes to go round the orbit.
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P3 1.8 Satellites

  • A satellite in a geostationary orbit has a period of 24 hours and stays at the same position directly above the Earth's equator.
  • Geostationary orbits are usually used for communication satellites.
  • Monitoring satellites are usually in low polar orbits.
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