June 23rd, 2018

Praxis: The science behind the curveball

By Medicine Hat News on June 17, 2017.

It’s that time of the year once again, time to get out and enjoy some of the local talent on the baseball fields. I do hope that many of you are taking advantage of the great outdoors and either watching or playing baseball right now. Of course, whenever I watch sports I am not just there cheering on my favourite team, I often think of science. Have you ever wondered what happens when a pitcher throws a curveball? Let’s get started!

* Remember to ask an adult for help before doing this experiment.


– sheet of paper

– scissors

– ruler

– pencil


1. Using the ruler, measure a strip of paper 3 cm x 30 cm.

2. Cut out the strip of paper.

3. Hold the strip of paper to your bottom lip.

4. Blow as hard as you can onto the surface of the paper.

5. Observe what happens.

What is going on?

Blowing on the strip of paper caused the paper to flip up. The force of your breath, or the stream of air coming out of your mouth “pushed” against the bottom of the paper. Because you were holding the paper with it hanging down, the force of your air caused it to rise up.

What is happening here is a scientific principle called Bernoulli’s Principle. Bernoulli’s Principle states that “as air (or any fluid) moves, it creates a region of low pressure. Low pressure has less “pushing force” than air of high pressure.”

When you blew across the upper surface of the strip of paper, you created low pressure. At the same time, air that was beneath the strip kept its normal pressure. The normal pressure is now greater than the reduced pressure at the top, resulting in the strip of paper being pushed up.

Something similar happens when a baseball is thrown. When a baseball travels through the air, the air flows around the ball. When the pitcher throws a curveball, part of the spin on the ball is in the direction of the flow of air and part of it is in the opposite direction. When the flows of air are in the same direction, it speeds up the ball. Just as you saw in this experiment, as the speed increases, there is a small decrease in air pressure on that side of the ball and the ball moves in that direction. At the same time, the higher pressure is also pushing the ball on the other side. This results in a curveball.

If this activity was interesting, make sure you investigate more Sports Science at our summer camp at Medicine Hat College this summer!

Patty Rooks is senior scientific consultant at PRAXIS, “Connecting Science To The Community.” Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook.

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