Gravity

• Gravity is one of the most important forces in the universe.
• An object with mass in a gravitational field experiences a force known as weight.
• The more mass an object has, the greater its gravitational field will be.
• Weight is the force acting on an object due to gravity - it has the unit newtons (N) and acts towards the centre of a gravitational field.
• The weight of an object can be measured using a calibrated spring-balance, often called a Newton meter.
• Weight is a non-contact force.
• The push or pull acting between objects that are not physically touching when they interact is known as a non-contact force.
• An object does not need to be touching the Earth to have a weight.
• Gravitational field strength ( g ) is measured in newtons per kilogram (N/kg).
• The Earth's gravitational field strength is 9.8 N/kg.
• For each kg of mass, an object will experience 9.8 N of force in the Earth's gravitational field.
• Where there is a weaker gravitational field, the weight of an object is smaller.
• The gravitational field strength of the Moon is 1.6 N/kg.
• For each kg of mass, an astronaut will experience 1.6 N of force on the Moon.
• Astronauts on the International Space Station appear to be weightless because both they and the space station are constantly falling towards the Earth.