The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan

T.H.

Walk Tall

(Lie down taller!)

PDST Resources for Leaving Certificate Physics 2

An Old Wives’ Tale?

It used to be said that you’re taller in bed than standing up. Is this true?

PDST Resources for Leaving Certificate Physics 3

Measuring height

Use a hardback copy to mark top of head and make sure it’s horizontal. Measure from floor to hardback. Make sure the metre sticks are vertical.

This student’s height when standing was 179 cm.

PDST Resources for Leaving Certificate Physics 4

... and lying down

Then lie down with your feet touching the wall. Use a hardback copy to mark the top of the head. Measure from the wall to the hardback

Lying down, this student’s height was measured as 183 cm.

PDST Resources for Leaving Certificate Physics 5

The old wives were right!

This student’s height was 179 cm standing up and 183 cm lying down. What was the percentage increase in height?

Why do you think he was taller lying down?

PDST Resources for Leaving Certificate Physics 6

Answer 1: Percentage Increase

The percentage increase was:

183 179 100 2.2%179 1

PDST Resources for Leaving Certificate Physics 7

Answer 2: Why?

The spine is made of small bones called vertebrae.

Between each vertebra is a fluid filled disc.

Standing up, your own weight slightly compresses these discs.

Lying down, the discs are under less pressure and have more volume.

PDST Resources for Leaving Certificate Physics 8

I don’t get it?

You are not as tall standing up because your weight slightly squashes the discs in your spine.

These discs behave like water balloons.

Try this yourself. How much taller are you lying down?

PDST Resources for Leaving Certificate Physics 9

Further Questions

Would someone be taller standing on the moon than standing on earth? Why?

Find the average difference in height standing vs. lying down for your class.