Science Smarts: Line ’em up and knock ’em down

By Patty Rooks on July 26, 2025.

It is one of my favourite times of the summer in Medicine Hat – Stampede time!

I have absolutely loved wandering the grounds and taking part in everything there is to offer. Something that has always baffled me are the games. How come I never win? I think we had better investigate this further. Let’s get started!

*Remember to ask an adult before doing this experiment.

Materials

• Tennis ball

•

Three identical clear water bottles

• Water

• Food colouring

(three different colours)

• Very sturdy table

• Outdoor location

to throw things in

• Science notebook

• Pencil or pen

• Masking tape

Procedure

1. Fill the water bottles with water and add a few drops of food colouring. I think that each bottle should have a different colour! Put the lids on TIGHT so they do not spill.

2. On the table, line the bottles up in a pyramid shape – two bottles on the bottom and one on the top – just like they do at the Stampede.

3. Measure two meters away from the table and put a line here with the masking tape. Everyone has to stay behind this line in order to throw the tennis ball.

4. Get ready. Stand behind the line and throw the tennis ball at the bottles.

5. What happens?

6. Record in your science notebook how many bottles (if any) you knocked over).

7. Repeat 10 times and think about where you are aiming the ball in order to know the bottles over.

8. Let’s mix things up a bit.

9. Empty the water out of the bottle on the top of the pyramid and then replace it.

10. Throw the ball at least 10 times again and record your results.

11. For the last “test”, empty one more water bottle.

12. Stack the water bottles in a pyramid again BUT with the two empty bottle son the bottom and the full one on the top.

13. Test by throwing ten more times and record your results.

14. Analyze your results.

15. What do you notice?

What is going on?

You should have noticed that the pyramid you built last was easiest to know over the most bottles. One of the reasons for this is that it was VERY unstable. Another factor in how many bottles you were able to know over involves where you hit them. With the different configurations, you changed the centre of mass in the pyramid. In order to knock these bottles over, you had to throw your ball and hit the centre of mass with a good amount of force. When you had all three bottles full of water, the centre of mass is actually closer to the centre of the two bottom bottles (I bet you threw the bottle at the middle of the bottles). Because the bottles are all full, you also need a bit of force with your throw in order to knock them over.

Always remember hit just BELOW or at the centre of mass in order to be successful. Good luck at the midway games – now you have a bit of knowledge in order to win the giant teddy bear!

Mark your calendars for the praxis AGM on Wednesday, Sept. 17 at 7 p.m. We are always looking for new board members that want to share their love of science. Contact Praxis for further details.

Patty Rooks, senior scientific consultant Praxis Science Outreach Society. Praxis has moved! We are very fortunate to be located in the Community Futures Entre Corp Building at #202 556 Fourth St. SE, Medicine Hat, Alberta, T1A 0K8. For all your science needs, please email praxis@praxismh.ca.

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