New for 2010.
The Challenge:
Split the group into two teams. This could be two groups of children at schools or a child and their parents at events.
Each team gets a trebuchet.
Compete to try and launch the bean bag the furthest or to get the bean bag into a box if space is limited.
Optional challenge to beat the day's record.
Explanation:
The trebuchets can be modified in two main ways, the pivot position and and the angle of release.
The optimal pivot position seems to be the third or fourth hole from the weight (don't tell them this). With the weight close to the pivot, it cannot accelerate the arm fast enough. This can be explained via the analogy of opening a door via pushing it near the hinge, which is much harder than doing it normally. However, with the mass too far from the hinge, the acceleration of the arm is greater, but speed of the bean bag end is small as it is now too close to the pivot. This time, the structure of the trebuchet also needs to be taken into account, as the weight hits the ground before completing the full swing. As it is not good at either end, the best position needs to optimise the balance between these two ideas.
The angle of release can be altered by the position of the spaghetti spoon launcher. The best launching angle should be 45 degrees, or a bit less accounting for air resistance. However, it will not necessarily fire at the same angle when the pivot position changes so this may also have to be adjusted.
Some of the bean bags have a string attached, which act as a sling to launch the projectiles further. At the moment that the bean bag leaves the trebuchet, it is swinging relative to the arm, so its relative speed adds up with the normal launch speed. Show them this after they have tried it normally.
Things to talk about:
* Levers: the more the distance to the pivot the less the force, but the greater the distance moved. It might be worth starting off with a brief explanation of how levers work using an arm.
* Why it's best to have the projectile far from pivot.
* Angle of release: 45 deg should always be best for range, neglecting wind. How can we control the angle? - the rabbit is ejected from the trebuchet when centrifugal force overtakes any force the holder exerts on it. (Centrifugal force gets bigger as the arm accelerates through the swing.)
* Using a sling to get extra velocity.
(more suggestions welcome)