Nail balancing challenge

This activity is part of our Science Lab series. Check out the ANU Science Lab for more experiments! In this activity, you will tackle the nail balancing challenge to explore center of gravity, torque, and structural stability by balancing six metal nails on the head of a single upright nail. Watch the video above to see how it is done.

Nail balancing challenge materials & ingredients

For this activity:

• 7 large steel or iron nails (flat-headed nails work best)
• 1 small wooden block
• A hammer (to secure the base nail)

Safety Note: Always get adult supervision when using a hammer to drive the base nail into your wooden block, and take care when handling sharp nail points.

How to balance nails: Step-by-step instructions

Step 1: Set up the base nail

1. Hammer one nail vertically into the center of your wooden block so it stands straight and sturdy with its flat head pointing upward.

Step 2: Build the interlocking nail lattice

1. Lay one nail flat on the table. This acts as your main bottom support beam.
2. Arrange four nails crosswise over the support beam in an alternating pattern: place two nails with their heads resting on the beam facing downward, and two nails with their heads resting on the beam facing upward. This balances the weight evenly across both sides.
3. Lay the sixth nail directly over the top of the middle crosswise nails, running parallel to the bottom support beam with its head facing the opposite direction of the bottom nail.

Step 3: Lift and balance the structure

1. Pinch the ends of the top and bottom parallel nails together tightly to lock the four crosswise nails into a rigid frame.
2. Carefully lift the entire interlocked 6-nail structure off the table in one piece.
3. Balance the center of the bottom support beam directly onto the flat head of your upright base nail!

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How the nail balancing trick works: The science explained

This physics demonstration works due to two key mechanical principles: weight distribution and center of gravity.

• Symmetrical Weight Distribution: Because the nail heads are alternating, three heavy nail heads sit on the left side and three sit on the right, ensuring symmetrical mass distribution around the central axis.
• Lowering the Center of Gravity: The center of gravity is the single point where the total weight of an object is balanced. In this interlocked structure, the four crosswise nails hang downward below the pivot point (the head of the base nail).
• Stable Equilibrium: Hanging the heavy parts of the nails downward shifts the overall center of gravity to a point located below the actual pivot point. Because the center of gravity sits below the support point, the structure enters a state of stable equilibrium. If you nudge or flick the structure, gravity naturally pulls it back to its central resting position rather than letting it tip over!

Science fair projects & taking it further: Experimenting with variables

• Add more nails: Can you modify your interlocking pattern to balance 8, 10, or even 12 nails on top of a single base nail?
• Asymmetrical weight: What happens if you place three nail heads on one side and only one head on the other side? Can you adjust the balance point on the base nail to keep the structure standing?

Enjoyed this experiment? Explore more hands-on activities on the Science Lab ANU YouTube channel.