How can we use a catapult to study the properties of skipping stones in physics?

[ponjavic]

We are the same Swedish team competing in a worldwide Young Physicists tournament for K-12 students.
We're currently getting a grasp of the formulas involved and meanwhile we need a way to prove them.

Or initial idea is to create some sort of catapult with which we can slung a stone at a specific angle and with a specific force. Then we study its properties after an initial skip.

Any ideas on how the expermient could be conducted and also how properties after initial jump could be gathered would be very helpful.

//Aleks

 

[ponjavic]

Would a camera suffice for measurements?

 

[ponjavic]

No one with ideas? A standard PAL 24 frames/s didn't work so that will have to be skipped.
Any other ideas?

 

[Gokul43201]

The problem with this experiment is "repeatability". Even if you can find a good way to measure the skip legths and so on, can you claim that you skipped the same stone 5 times and it gave the same results each time ? It's hard to repeatably control the dynamic orientation of the stone - especially with a catapult. And without repeatability, an experiment has no value.

If you still want to do this experiment, consider making a spring loaded launcher, with a flat take-off ramp. Also I would buy/make uniform circular discs to be used as stones. You've got to be very careful and patient if you want repeatable measurements.

I would imagine a 24 fps camera should work - as long as you capture the ripples on the water surface, you can determine the bouncing point.

 

[ponjavic]

what you recommend is actually what I've been think about, except for the fact that 1/24 didnt and won't work.

I'll try it out tomorrow if I'm able to create the perfectly circular stone...

Another problem i can't launch it from a pad as it then will tilt downwards as it hits the water it needs a / tilt in order to skip...

 

[Gokul43201]

It's most important to get the disc spinning, or else nothing will happen.

 

[ponjavic]

Not true, the spinning is only for containing angles as for a gyroscope so for one throw (which the problem states i shall examine) spin is not necessary if you throw it perfectly. but naturally for a person throwing spinning is necessary.

 

[Gokul43201]

Spinning increases the stability tremendously. If you have a perfectly designed launcher, and the air is calm when you launch, then you could get by without spinning.