Nail Trick

In this activity you can balance 15 nails on the head of one nail.

Year groups: 3-6 (ages 7-11)

Educational objective

To see that using gravity to balance and counterbalance nails can produce some spectacular results.

Key student learning

A nail will balance on the head of another nail if its weight is evenly distributed (i.e. laid across it with half the weight on either side).
Many other nails can be balanced across the first nail if their weight is evenly distributed and if they can be stopped from slipping off.
A nail on top will push against the heads of the balancing nails, and as gravity pulls them down this will hold them more tightly in place.

Materials needed, per group

1 flat piece of wood or ball of modelling clay
15 nails (with ends rounded off for safety)

Open-ended investigation

This activity works best as an open-ended challenge. Click here for a guide to planning open-ended investigations in your classroom and use the activity sheet only as a last resort, once one child or group has already cracked it, to enable the rest to become experts.

Practicalities

If you want to assemble the equipment quickly, fix the nail upright in a ball of modelling clay or use any smallish flat piece of wood and hammer the nail into the centre. If you want to repeat this activity, cut a piece of wood or MDF approximately 10 cm square and drill a partial hole in the centre that is just wide and deep enough to accept the first nail. This apparatus can then be taken apart and stored flat when not in use.

The larger the nails, the easier and more impressive the activity is, so get the largest ones you can find (make sure you sand down the sharp points).

Discussion

How many of these nails can you balance on the head of one nail?
What’s the best way to balance one nail?
How can you get the other nails to balance on this one? (You can take it off and lay it flat on the table at this point.)
What can you use to hold down the nails lying across the first nail so that they don’t fall off when you lift them back on the nail head?
How does this trick work?

Look at the crane in the picture. How is it able to pick up very heavy weights without falling over?

Extensions

What is the maximum number of nails you can balance in this way? Try making a second row and balance it on top of the first. How many layers can you balance in total and how many nails does this use?
Can anyone find a different way of balancing the nails?
Can you scale up this activity, for example using hockey sticks instead of nails?
Can you scale down this activity using pins? (This is much harder; again, watch out for the sharp points.)

Links to everyday life

Cranes
Cranes use a counterbalance - a heavy weight at one end of the arm that stops the crane toppling over when it picks up a weight at the other end of the arm. This makes cranes very heavy and hard to transport, so some have been designed to use a refillable water tank as the counterbalance to make them lighter and easier to transport.

Cantilever bridge
The railway bridge across the Firth of Forth in Scotland contains almost 54,000 tons of steel. When it was completed in 1890 the 2.2-km-long bridge was the biggest in the world. It is the world’s oldest cantilever railway bridge and remains in use to this day.

Launchball links

Launchpad

Educators' Information