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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