What it shows
A soft cushion makes the egg stop more slowly, so the force on it is smaller. The same change in motion over a longer time means a smaller force.
The science
An egg falling from rest gains speed. When it hits the ground, its speed drops to zero. Force equals the change in momentum divided by the time of the stop, so a longer stopping time means a smaller force. Cushions squeeze and slow the egg over a few centimetres instead of a few millimetres, which spreads the stop over more time and reduces the force that cracks the shell.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- 6 hard boiled eggs, in zip bags
- Cotton, crumpled paper, sponge and shredded cloth
- Small cardboard boxes, 6 of equal size
- Tape
- A ladder or a first-floor balcony, with an adult
- A tray of soft soil or sand to land on
- A tape measure
Safety
For this project: An adult must do the drops from height and keep the area below clear. Use boiled eggs, and wash hands after touching raw or boiled egg shells.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Put each boiled egg in a zip bag so that any breakage is easy to clean.
Pack the first egg in a box with no padding as the control, the second with crumpled paper, the third with cotton, the fourth with sponge and the fifth with cloth.
Close and tape each box so the egg stays in the centre.
Drop each box from a height of 1 m onto the sand tray and check the egg for cracks. Mark crack size on a scale from 0 to 3.
Increase the height to 2 m and then 3 m with an adult and repeat for the boxes that survived.
Write the results in a table with the material and the highest height without damage.
Draw a bar chart of the greatest safe height for each padding.
Weigh the filled boxes and say which padding gives the best protection for its mass.
What you should see
The unpadded egg cracks at once, the soft paddings protect it from higher drops, and the best padding is the one that squeezes and slows the egg for the longest distance.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why does padding protect the egg?
It lengthens the time of the stop, so the force on the egg is smaller.
2What is momentum?
Mass times velocity.
3Why do car seat belts and airbags work the same way?
They slow the body gradually and so reduce the force.
4Why was the same drop height used for each box?
To keep the test fair, since a higher drop gives more speed on landing.
Take it further
Add a paper parachute to the best box and see how much it raises the safe height.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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