Weight is measured in grams and kilograms

1000g = 1kg

e.g. 2500g = 2.5kg 

Maths problems kindly provided by Twinkl.ie

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Stretchy Science

This activity uses how far an elastic band stretches to work out how heavy something is compared to other objects.  

What you need – Elastic, clothes pegs / bull clips, a selection of objects to weigh, a long stick or broom to tie to elastics to, 2 chairs to rest the broom or stick on, ruler or measuring tape, weighing scales. 


  1. Tie your clips to your elastics 
  2. Tie the elastic on to the broom.  All elastic should be equal length.

  3. Clip on you objects 

  4. Observe how much each object has stretched the elastic. Can you tell which is the heaviest and which is the lightest? 
  5. Measure how far the elastic has stretched and note it down in a table like below.
  6. Estimate the weight of the object and then weigh it to see how to close you were.
 Object   Length Stretched   Estimated Weight   Actual Weight 

Wait, there's one more weight experiment!

Did you know air actually weighs something? It's true! And this experiment proves it. 

What you will need – Two balloons blown up to the same size, a wooden ruler, string / thread / wool, a small pin / needle. 

  • Tie a piece of string around the middle of your ruler and attach it to the broom you had set up from the previous activity.  
  • Attach a piece of string of equal length to each of the balloons.
  • Tie the string with the balloon to each end of the ruler. 
  • Move the string in the middle of the ruler until the balloons are balanced and one side is not tipping down more than the other and is parallel to the floor. 

  • Now get your sharp object and pierce the balloon, at the base so it doesn't explode, and let the air come out. 
  • What has happened? 
  • Why has this happened?  

The balloon that is still full of air causes the ruler to tip, showing that the air in it has weight. 

Send us pictures or videos of what you have done. Ask your parents to help you send them to rte.ie/learn

Answers – 1) 21.4kg / 21,400g 2) 2kg / 2000g 3) 2.35kg / 2350g 4) 3.43kg / 3430g 5) 1.6kg / 1600g 6) 7.28kg / 7280g