An experiment with a 330ml drinks can to determine how much water is required for the can to balance on its edge.

A typical 330ml can, typically associated with soft drinks, can be made to balance on the edge of its bottom rim, provided the can is filled with a certain weight of liquid.

The reason for this is that the contents of the can affect the can’s centre of gravity. The centre of gravity is the point through which an object’s weight passes. If the weight acts over an object’s base, the object will remain in place. If the weight acts outside the base, the object will fall (1).

In an empty can, the centre of gravity is also the geographic centre. The addition of mass inside the can, however, shifts the centre of gravity, thus changing how the can balances. With the correct amount added, the CoG can be shifted to allow weight to still act over the base even when the can is significantly tilted (2).

If, though, too much mass is added to the inside of the can, it may push the centre of gravity back outside the base. This is because the increase in volume forces some of the mass to sit above the pivot point, thus cancelling the effect of the mass below.

In this instance, a can was filled with multiple quantities of water, and then tested to see whether it could balance. The results are shown below.

By process of trial and error, it was determined that the optimum range for the amount of water used is approximately 0.025 – 0.200 kg (or 25 – 200 ml), though the reliability of these results is questionable due to the accuracy of the measuring equipment, and the loss of water during transference. Based on the figures obtained, the mean amount of water to perfectly balance the can would be 0.1125 kg (or 112.5ml)