# P3 1 Turning Forces

Key points of P3 1 - Turning Forces.

HideShow resource information

## 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.
1 of 8

## 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.
2 of 8

## 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.
3 of 8

## 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.
4 of 8

## 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
5 of 8

## 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.
6 of 8

## 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.
7 of 8

## 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.
8 of 8