Although the video was originally uploaded in 2006, it is still interesting to see a cannonball float.
Obviously a cannonball doesn’t float in water but because mercury is so dense, the mass of a cannonball is not enough to break the surface! The video was originally produced by BBC.
If you’re interested in why a cannonball will float in mercury but not in water, check out the small table I have put together below. We can see that at 20°C, mercury is more than 10x more dense than water.
Density of water compared to the density of mercury: