Sink or Float- Experiment Bar - 1 of 3
Will a Bowling Ball Sink or
Float Demonstration
Brief Summary
In this demonstration, you will place several balls of different size, weight, mass, and density
into a tub of water to see if they will sink or float. Visitors will learn the difference between
weight, mass, and density.
Equipment Required
What you need:
1. 6 lb bowling ball
2. 12 lb bowling ball
3. 6 lb exercise ball
4. Various assortment of other balls
5. Tub of water
Sink or Float- Experiment Bar - 2 of 3
Main Teaching Points
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Density is the degree of compactness of a substance. Mathematically, density is mass
divided by volume.
In physics, mass is a measure of resistance to acceleration when a force is applied.
Mass is constant in different gravitational fields, unlike weight. This is why we typically
talk about the mass of a planet or other celestial objects.
Weight is mass multiplied by the acceleration due to gravity. We are used to talking
about weight on Earth, but if we traveled to another planet, our weight would change
but our mass would not. For example, if a rock weighs 100 lbs. on Earth, it would only
weigh 37 lbs. on Mars.
Saturn is the only planet in our solar system that is less dense than water. (It is about
70% as dense as water, and so would float in a giant tub of water with about 70% of
Saturn below the water and 30% above.)
Set Up
1. Take all supplies out of designated cabinet
2. Fill tub with water from experiment bar sink
3. Set up all balls in an easily accessible area, in designated round “tubs” to avoid them
rolling away
Suggested Ways of Presenting this Demo
1. Hold up 6 lb. bowling ball and ask who thinks it will sink or float. (This is a good place
to get more visitors involved because you can go around and ask people individually,
including people at the periphery.) (It floats.)
2. Hold up 12 lb. bowling ball and ask who thinks it will sink or float. (It sinks.) Have
visitors suggest why the 6 lb. one floats and the 12 lb. one sinks.
3. Hold up the 6 lb. exercise ball and point out that it is the same weight as the 6 lb.
bowling ball which floats. Ask who thinks it will sink or float. (It sinks.)
4. Why does the bowling ball float but the exercise ball sink? The same mass is
compacted into a smaller volume in the exercise ball, so the exercise ball is denser. It
is denser than the water.
5. Explain that Saturn is the only planet in the Solar System that would float in water.
However, it floats about 70% of the way into the water. Demonstrate this by pushing
the 6 lb. ball down so it is 70% of the way in.
6. May extend facilitation with other balls provided.
Operating tips
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Fill tub with cup or other container, to avoid having to lift tub out of sink after filled
Take Down Procedure
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Take balls out of tub
Slowly dump water from tub into sink
Dry off all balls and tub with rags under experiment bar sink.
Put back in designated cabinet
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Additional Science Content
More information on density:
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In Figure 1, the 6 lb. ball is floating in the water. That means that the rest of the water
has enough lifting power to hold the ball up. This is denoted by the arrows.
In Figure 2, you can see that the truth of the matter is that those “arrows” could hold up
6 lbs. of anything. It could hold up a 6 lb. ball OR 6 lbs. of water. Since 6 lbs. of water
would just fit into the “hole”, you can see that the amount of water that the bowling ball
displaces when it is floating must be 6 lbs. of water.
In other words, an object floats at the point that it displaces its own weight of water.
If the object is too dense, like the 6 lb. exercise ball is, than as you lower it into the
water, it is physically too small to displace enough water to match its weight, so it
sinks. The rest of the water does not have enough lifting power.
With the three balls listed above, you have two that are the same size, but different masses,
and you have two that are the same mass, but different sizes. Use these to help visitors get
their minds around the idea of density.
By the way, the thing that makes a Black Hole a Black Hole is not its mass, it is its density.
Black Holes are extremely dense. The material in them is compacted to the extreme.
Background Materials
collections links)
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(websites,
videos,
articles,
digital
https://www.stevespanglerscience.com/lab/experiments/floating-and-sinking-bowlingballs/