Mass & Weight

Mass and weight are not the same.
The mass of an object is how much matter it contains. It is measured in grams (g) or kilograms (kg) but is NOT a force.
The weight of an object is the force caused by gravity pulling down on the mass of an object. It is measured in newtons (N).

Measuring weight

Weight is measured using a forcemeter. The bigger the weight attached to the forcemeter the more the spring inside the forcemeter stretches.

A Forcemeter. Credit goes to BBC KS2 Bitesize
A Forcemeter. Credit goes to BBC KS2 Bitesize



Mass is a measure of how much stuff is in an object. Weight is a force acting on that stuff.
Weight is the result of gravity. The Earth's gravity attracts objects towards the centre of the Earth and you feel forces like this as weight.
Here is the equation that links weight, mass and gravitational field strength:
W = m × g
  • Wis the weight in newtons, N
  • mis the mass in kilograms, kg
  • g is the gravitational field strength in newtons per kilogram, N/kg.
You would weigh less on the Moon because the gravitational field strength of the Moon is one-sixth of that of the Earth. But note that your mass would stay the same. For example, what is the weight of an 80 kg person on Earth and on the Moon?
On Earth, g = 10 N/kg, so W = 80 × 10 = 800 N.
On the Moon, g = 1.6 N/kg, so W = 80 × 1.6 = 128 N.
Now try this quiz..