7.1.2 Gravitational Field Strength

• There is a universal force of attraction between all matter with mass
  • This force is known as the ‘force due to gravity’ or the weight

• The Earth’s gravitational field is responsible for the weight of all objects on Earth
• A gravitational field is defined as:

A region of space where a mass experiences a force due to the gravitational attraction of another mass

• The direction of the gravitational field is always towards the centre of the mass
  • Gravitational forces cannot be repulsive

• Gravity has an infinite range, meaning it affects all objects in the universe
  • There is a greater gravitational force around objects with a large mass (such as planets)
  • There is a smaller gravitational force around objects with a small mass (almost negligible for atoms)

The Earth's gravitational field produces an attractive force

• The strength of this gravitational field g at a point is the force F per unit mass m of an object at that point:

• Where:
  • g = gravitational field strength (N kg^-1)
  • F = force due to gravity, or weight (N)
  • m = mass (kg)

• This equation shows that:
  • The larger the mass of an object, the greater its pull on another object
  • On planets with a large value of g, the gravitational force per unit mass is greater than on planets with a smaller value of g

• An object's mass remains the same at all points in space
  • However, on planets such as Jupiter, the weight of an object will be a lot greater than on a less massive planet, such as Earth
  • This means the gravitational force would be so high that humans, for example, would not be unable to fully stand up

A person’s weight on Jupiter would be so large that a human would be unable to fully stand up

• Factors that affect the gravitational field strength at the surface of a planet are:
  • The radius (or diameter) of the planet
  • The mass (or density) of the planet