weight, mass and gravity

• • gravitational force is the force of attraction between masses
  • gravity attracts all masses, but is only noticed when one of the masses is large like a planet
  • anything near a planet or star is attracted to it very strongly
  • this causes everything on the surface of the planet fall to the ground and gives everything a weight
• • weight is the force acting on an object due to gravity
  • the force of gravity close the Earth is due to the gravitational field around the Earth
• • the weight of an object depends on the gravitational field strength at the point where the object is
• • weight is calculated by:
  • weight = mass x gravitational field strength
• • the weight of an object can be considered to act on a single point
  • this is known as the centre of mass
• • weight and mass are directly proportional
  • weight is measured using a calibrated spring-balance, which is known as a newtonmeter