Gravity is a pull between all objects. The Earth is so huge that its gravity pulls everything towards its centre: that is why a dropped ball falls down, whichever side of the Earth you are on. The pull of gravity on an object is its weight, measured in newtons with a forcemeter.
Mass is how much matter is in an object, measured in kilograms. On Earth each kilogram weighs about 10 newtons. On the Moon gravity is weaker, so you would weigh much less, but your mass would be the same. A heavy and a light ball dropped together hit the ground at almost the same time; a feather falls slowly only because air resistance pushes on it.
Worked example
A bag has a mass of 3 kg. What is its weight on Earth?
- On Earth each kilogram weighs about 10 N.
- 3 × 10 = 30.
Answer:The weight is about 30 N.
Key words
- gravity
- the force that pulls objects towards each other and towards the Earth
- weight
- the force of gravity on an object, in newtons
- mass
- the amount of matter in an object, in kilograms
- forcemeter
- a tool that measures forces in newtons
New questions every time.
NGSS-referenced: 5-PS2-1