please help! =)

[ahmee]

Hi everyone,

I'm building a catapult for my physics project where my throwing arm can be only 50cm (which is pretty short) long from the pivot point and it should weigh relatively light. I have to throw a hackysack 25 meters or more to get a good grade, but so far I can only manage to throw it around 10 meters. Does anyone have any ideas on how to improve the distance? Thanks! =)

[robertzhou]

Try a Google search on "how to make a catapult" and you'll get lots of googideas.

Here's a good idea I found:
click here

[deleted-71254]

The goal of 25 meters is interesting... and only 50cm of throwing arm?

Robert suggested a link to a site showing a trebuchet, which has the advantage of using a rope (string in the case of a scale model) to extend the throwing arm. Is that allowed under the rules of the project?

A trebuchet stores its potential energy in the form of a counter weight on the other end of the throwing arm. The more the weight, the more the energy available. As it falls, it transfers the energy to the much smaller mass projectile on the other end of the throwing arm plus rope.

A catapult stores its potential energy in the form of a tension spring. The more tension, the greater the energy. To get a hacky sack to travel 25m the energy would have to be pretty high... since the acceleration of the projectile plus the mass of the thowing arm must be very high to get the projectile up to speed.

Have you determined the best angle of launch? What do the rules say about height above the ground of the launching arm? The classic solution to the best distance problem is that from a ground launch, the angle of release should be 45 degrees. But for a catapult to accelerate from zero to 45 degrees seems limited. Perhaps you can get more distance by raising the catpult and allowing it more swing? Also, the higher the launch point, the more time you will have in the air... also, that will mean that the launch angle will be lower, giving you slightly more swing distance before release.

Please give us more details and keep us informed?

Good luck !

[ahmee]

Hi,

Thanks for all the advice but I didn't have time to change/add things to my catapult because I had to turn it in today. I really appreciate your help though. I learned a lot more new things from this. I'll keep all of the advice in mind...in case I have to build another one sometime in the future. Once again, thanks a lot! =)