well... as for displaying how it works, wouldn't the objet moving be evidence of the force?
as for figuring out force, u need it to be traveling 1cm/min idealy on average
make a graph of distance over time, that being 30cm over 30 mins, take the dirivative(sp?) to get speed(remember u have...
find how high and how far it goes, if it's a moderately sized catapult air resistance shouldn't be a problem... take the height to figure out it's original speed in ^ that direction, then take the distance along with it's flight time to find it's speed(which should remain close to constant) in >...
Me and my roommate are having a debate about how speakers work... He says that speakers use ohms, he came to this conclusion after the guys at best buy told him that his speakers "didn't have enough ohms"
I said that speakers use volts not ohms to work, and that the ohms are just a property...