Rube-Goldberg Catapult

Team members: Rob Burgin Craig Bowers Aaron Shannon James Hartsig

Overview

A three step Rube-Goldberg device with the purpose of shooting a ball via catapult

The first step involves a ball traveling down a PVC pipe triggering a mouse trap upon landing

In the next step, the mouse trap pulls the firing pin out of the catapult

The last step involves the firing of the catapult

The Rube-Goldberg Catapult

Energy Conversions

The first step involves a ball with gravitational potential energy ( Ugrav =

mgh ) which gives us (0.25 kg)(9.81 m/s/s)(0.1588 m) = 0.0389 Joules to trigger the mouse trap.

The mouse trap exerts elastic potential energy ( Fd = E ) which gives us (136 N)(0.08m) = 10.88 Joules which then converted to kinetic energy. The force required to pull the catapult pin is 1.5 N.

Since the catapult uses springs, the energy requires a spring constant. The spring constant, K, can be calculated by measuring the force per length deflection from the neutral position. A force of 34.5 N is required to obtain a deflection of .292 M. K is then equal to (34.5 N)/(.292 M)= 118 N/M for each spring. The elastic potential energy can be derived from this using ( ½ Kx2 ) multiplied by two (springs) which gives us 118N/M(.292M)2=10.06 Joules.

All potential energy used in this device converts to kinetic energy.

Conclusion

The device is very simple and reliable The most difficult part was accounting for

energy lost during the process The calculations were very straight forward

when nonconservative forces are emitted We feel that no changes are necessary