How tall are you, really?

You might think you know your height, but this activity might change your mind. How tall are you, really?

You will need

Masking tape
Pencil
Bookend (or something with a right angle, such as a set square or hardback book)
Tape measure
An adult to help, and to experiment on
If you’re much shorter than your adult, you’ll need a small ladder, so you can reach the top of their head

What to do

Someone is standing next to a wall. Someone else is holding a book end above their head.

Early in the morning, wake up your adult volunteer.

Put a strip of making tape all the way up a wall.

Make sure you both take your shoes off.

Stand up straight, with your heels against the wall. Try to stand as tall as possible.

Get your adult to hold the bookend against the wall. One side should touch the wall, while the other side should jut out from the wall and touch the top of your head. Mark the height of the bookend’s base on the tape. Don’t draw directly on the wall!
Compare your morning height and your evening height. Are they the same?

Now, swap roles. Get your adult to stand against the wall while you mark their height.

Label the two heights with your names and the time. Remember to keep the tape on the wall for later.

You can measure the heights with your tape measure as well, and write it down for safekeeping.

At the end of the day, repeat this activity. Mark your height and your adult’s height on the same piece of tape. Remember to label them again with your names and the time. Has your height changed throughout the day?

What’s happening?

When you’re a kid, you might think you’re always growing taller. But your height is continually see-sawing. You get shorter during the day and taller at night.

The reason why you shrink and grow is also the reason you can bend your back. Your spine is made of lots of small bones called vertebrae. In between vertebrae, there are lumps of softer material, known as discs. Apart from allowing you to bend your back, they also act as shock absorbers, protecting your spine when you run and jump.

Over the course of a day, the weight of your body and the shocks of your life press against the discs in your spine. The discs slowly squash down and become shorter. As you sleep, there is no pressure on your spine and the discs expand again.

You may notice that your height changes a different amount to other people. An adult may have a taller spine, and they might be heavier. Your spine might be younger and better at recovering overnight, or you might run and jump a lot more than your volunteer. There are lots of different things that affect how much your height changes throughout the day.

If you want to learn more, maybe you could take measurements each day for a week, and see if there are any patterns you notice!

More information

Learn about what happens to your spine in space

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