Sinking and Floating Bowling Balls

Sinking and Floating Bowling Balls Written by Steve Wojtas

1ST SCIENTIST Hello everyone. My name is ----

2ND SCIENTIST And I'm -----

1ST SCIENTIST And we're going to show you why science is such an important tool to explore the world around us.

2ND SCIENTIST Here we have a fish tank filled with water and three different size bowling balls. “1st” is going to put this bowling ball in the tank. It feels pretty heavy.

2nd passes ball to 1st.

1ST SCIENTIST It is pretty heavy. But in science we like to be exact. So let's use this scale to measure it's weight.

2ND SCIENTIST How much does it way?

1ST SCIENTIST <11 pounds.

2ND SCIENTIST Excellent. So in science, we want to predict what will happen when we put the bowling ball in the tank. Do you think it will sink or float?

Audience responds.

1ST SCIENTIST Well, now let's test your hypothesis.

1st places the ball in the tank and it floats.

1ST SCIENTIST (CONT'D) What happened? Audience responds. 2ND SCIENTIST That's right, it floats. So some of you had your hypothesis proven correct and some of you had your hypothesis proven incorrect. But we all learned something. Even though a bowling ball is relatively heavy, it's not as dense …

1ST SCIENTIST … Meaning it doesn't have as much matter, or stuff inside it …

2ND SCIENTIST … Right, as the water had inside it. So the bowling ball floated because it's less dense than the water. So let's try it again with a ball of a different weight. How much does that one way?

1ST SCIENTIST This bowling ball measures in at (>12 lbs).

2ND SCIENTIST Excellent. So again, before we experiment, we want to hypothesize and predict what is going to happen. Is the ball going to sink or float?

Audience responds.

1ST SCIENTIST All right. Let's test your hypothesis.

1st places the ball in the tank and it sinks to the bottom.

1ST SCIENTIST (CONT'D) The ball sank to the bottom of the tank. 2ND SCIENTIST So this experiment had a different result because the bowling ball was more dense than the first ball. We can infer from these two experiments that the density of water is somewhere in between the densities of these two bowling balls. Let's do one more experiment with the tank. How much does that bowling ball weigh?

1st scientist measures the ball on the scale.

1ST SCIENTIST 11.5 Pounds.

2ND SCIENTIST All right, so that's in between our two bowling balls. So it has a chance to be either less or more dense than water. What do you guys think?

Audience responds.

1ST SCIENTIST All right let's see.

1st places ball in tank. It half sinks and floats.

1ST SCIENTIST (CONT'D) Well, that's interesting. It's half floating, and half sinking.

2ND SCIENTIST A surprising result right? Well, let's repeat the experiment to see if the same thing happens again.

1st places the bowling ball in the tank and this time it sinks to the bottom.

1ST SCIENTIST This time it sank.

2ND SCIENTIST So what was the difference? It was the same ball, same water, same tank, same good looking scientist. 1st smiles.

1ST SCIENTIST Well the only variable, the part that was different, was that the first time I put this ball in the tank, the finger holes were pointed down, while the second time they were pointed up.

2ND SCIENTIST So the first time, air was trapped in the finger holes, helping to lift the ball and making the whole object less dense compared to the water.

1ST SCIENTIST Right. That's why in science, we like to repeat things, and be really specific with our observations. Because then we have a much better chance of figuring out what happened. That's one of the reason's I love science--it can help us explain the unexpected.

2ND SCIENTIST And I'm sure a lot of what happened with the bowling balls was unexpected. The first time I did these experiments I thought they would all sink.

1ST SCIENTIST Science makes us go further than just using common sense or knowledge to predict and outcome, because only then can you really know what's going on in the world.

2ND SCIENTIST And that's one of the reasons Science is Fun!