Floating Bowling Ball Demonstration

Have you ever really thought about just how dense water really is? If you've ever carried a gallon of water you know that water is not very light. In fact, a gallon of water weighs about 8 pounds! But what does this have to do with bowling balls?

If you've ever been bowling you know that bowling balls range from about 8 to 16 pounds. However they are all the same size! This means that the average density of an 8 pound ball must be HALF the average density of a 16 pound ball. The inside of a bowling ball can get complicated but basically manufacturers vary the size, shape and material of the core of the ball to adjust the weight.

So if one gallon of water weighs 8 pounds and an 8 pound bowling ball takes up more space than a gallon of water, the ball will float!

Huh?

When an object is placed in water it will displace its weight in water (Archimede's principle). So the 8 pound ball (the red one on the left) is displacing 8 pounds of water but since it doesn't take up less volume than 8 pounds of water if floats. On the other hand, the 16 pound ball (the gray one on the right) is trying to displace 16 pounds of water but it has less volume than 16 pounds of water and sinks. OR we can just say the 8 pound ball is less dense than water and the 16 pound ball is more dense than water where density is the mass of the ball divided by its volume.

Eureka!

What about the sodas?

The sodas work the same way. The regular soda is sweetened by sugar - a whole lotta sugar. The diet soda is sweetened with an artificial sweetener (aspartame, nutrasweet...) but only a tiny bit. This means the regular soda is much more dense than the diet soda. However, both are denser than water - as is the aluminum can.

But I thought that objects denser than water will sink?

Don't forget the carbonation! The CO2 added to soda is enough to float the diet soda but not quite enough to float the regular soda.

The Optics of Floating Bowling Balls

There is much more than a density demonstration here.

• Total Internal Reflection: when viewed from a small angle it appears as if the bottom of the aquarium is a mirror but looking straight down reveals a Science House bookmark placed underneath.
• Refraction: when looking at the aquarium straight on you can see a 'break' in the ball at the surface of the water.

How can I make my own?

These are regular, ordinary bowling balls in plain aquarium. We suggest using an 8 pound ball for your less dense ball since it floats fairly high but a 9 or 10 pound ball will work just as well. Anything heavier than 12 pounds will sink. You can purchase the balls at a sporting good store or ask your local bowling alley for any balls it may be getting rid of.

Our balls do not have holes drilled since we leave them in the water for long periods of time and water can seep in and crack the shell of the ball. Holes do not affect the density of the balls enough to change the demo.

 

Teachers at the NSTA 2001 Conference
talking with Mike Smith - our floating bowling ball expert