Weight, mass and gravitational field strength

The weight of an object is the force on it caused by the gravity due to the planet. The weight of an object and the gravitational field strength are directly proportional. For a given mass, the greater the gravitational field strength of the planet, the greater its weight.

Weight can be calculated using the equation:

weight = mass × gravitational field strength

W = m \ g

This is when:

  • weight (W) is measured in newtons (N)
  • mass (m) is measured in kilograms (kg)
  • gravitational field strength (g) is measured in newtons per kilogram (N/kg)

Gravity on other objects in space

Space objectg, gravitational field strength (N/kg)
The Sun (star)293.0
Mercury3.7
Venus8.8
Earth9.8
Moon (satellite)1.7
Mars 3.7
Ceres (dwarf planet)0.27
Jupiter 24.7
Saturn10.5
Uranus9.0
Neptune11.7
Pluto (dwarf planet)0.49

Example

An apple has a mass of 100 g. Calculate its weight on Mars (g = 3.7 N/kg).

100 g = 100 ÷ 1000 = 0.1 kg

W = m \ g

W = 0.1 \ kg \times 3.7 \ N/kg

W = 0.37 \ N

Question

Calculate the weight of a 30 kg dog on the Moon (g = 1.7 N/kg).

W = m \ g

W = 30 \ kg \times 1.7 \ N/kg

W = 51 \ N