Homeschool Science – Do Bowling Balls Float or Sink?

This homeschool science experiment may just make you question everything you think you understand about physics – so be ready. In this experiment, you’ll get the real answers to whether or not all heavy objects sink in water. By working on this homeschool science experiment, you’ll also get a clearer understanding of how physics really works…and how nature can sometimes seem like it makes exceptions.

Before you get started, there are some materials you’ll need:
    •    An 11 or less pound bowling ball
    •    A 13 pound or more bowling ball
    •    One large aquarium or tub filled with water
    •    A 30-inch long piece of string
    •    A ruler
    •    A scale

Once you have these materials gathered together, you’re ready to get started by following these steps:
    •    Fill the aquarium or tub with water.
    •    Place the heavy bowling ball (do not drop it) into the water gently.
    •    Record your observations. Does the ball sink or float?
    •    Place the lighter bowling ball into the water.
    •    Record your observations.

What you observed:
The heavier bowling ball probably sank to the bottom of the water. The lighter bowling ball probably floated. The reason the heavier ball sank is because it is denser. Denser objects are more likely to sink whereas lighter objects are more likely to float.

So what is density? Density is a measure of the mass and volume of an object. Water has a density of about 1 gram per cubed centimeter. If an object has a greater density than water, then the object will sink in the water. However, if the object has a lower density than water, the object will float.

In order to determine the density of an object, you need to know the object’s weight and volume. Didn’t know you’d need to know math for this science project? Don’t forget that math and science often work hand-in-hand as you look for answers. And, by the way, this website is great for homeschool science resources.  

To find the volume of your bowling balls, measure the circumference of each ball. To measure the circumference, wrap a piece of string around the ball at the belly (widest part) of the ball. Measure the length of the string using a ruler. Chances are good that the circumference of you ball is about 27 inches.

The circumference of a sphere (remember, a bowling ball is a sphere) is two times pie times the radius. Now, to find the volume, use this equation: 4/3 x pie x radius cubed.

Next, you need to determine the weight of the bowling balls, which you can find out using your bathroom scale. To find the density of the bowling ball, divide the ball’s weight by the volume in cubic centimeters. If the density is greater than 1 g/cm cubed, the ball will sink. If it is lower, it will float.

This physical law is the same for all materials, including ships. For that reason, as long as even the heaviest of ships have a lower density than water, they will float. Now next time you see a ship floating by, you can explain to all of your friends why it floats! Pretty cool experiment, huh?