Weight a minute!

Activity overview

Run the activity

You will be zooming in and out of the image above – starting very close and stepping back slowly.

1. Start by asking everyone:

• What do they think the image is and why?
• What does the image remind them of and why?

2. Every time you zoom out, ask the class:

• Can they describe the colours, shapes and textures?
• What do they think the image is now – have they changed their minds?

Background science

On the surface of the Moon objects weigh less. This doesn't mean, however, that the mass of the object has changed. Let’s start by clearing up a common misconception children often have about mass and weight. Every object (e.g., the human body) contains a certain amount stuff – this is its mass. It doesn’t matter where you are in the universe, you always have the same amount of mass. The greater the mass of an object, the greater its gravitational pull, and vice versa. 

Your weight is measured by the force of gravity acting on your mass (pulling you down), so if the celestial object you are standing on is smaller than the Earth (e.g., the Moon), the force of gravity acting on you is less, so your weight decreases. The opposite effect is true of a celestial object bigger than Earth; e.g., if you were able to stand on Jupiter, you would be much heavier as the force of gravity acting on your mass would be much greater.  

The Moon is just over a quarter the size of Earth (27%) and its mass is only 1.2% the mass of Earth. It therefore has a significantly smaller gravitational pull. This means that your weight on the Moon is only 16.5% of what it is on Earth.  For example, an object weighing 100kg – roughly the weight of a newborn elephant – on Earth would weigh in at a meagre 16.5kg on the Moon – roughly the weight of a cocker spaniel!

The weaker gravitational pull on the Moon means that humans are able to do some incredible things. For example, you would be able to jump almost 2 metres straight up into the air on the Moon and throw a ball six times further!  This is also why the Apollo astronauts who landed on the Moon needed to learn how to walk differently in the Moon’s gravity. Astronauts have to do a funny hopping run as they move across the surface of the Moon, becasue if they tried to take normal steps, they would fly up into the air too far and fall over!

Take it further

Find out Your Weight on Other Worlds with this special online calculator or you might like to turn the activity in to a STEM project by challenging children to calculate their own weight or the weight of everyday items on the Moon.

Introduce your class to the concept of gravity with this learner guide and short videos from BBC Bitesize.

Take the learning even further with these forces and gravity lesson resources from STEM Learning.

Get your class’ imagination going with these Explorify questions:

• What if there was no gravity?
• What would you investigate on the ISS?
• What is there was no moon?