MYTHBUSTERS LAB

  For this lab, we had to disprove two commonly accepted myths. If you asked most people if they thought the myths we were presented were true or not, most people would believe that they were.  Even at first, our lab group had trouble disagreeing with these simple misconceptions.  After a while, we discovered that both myths were actually false in many situations.  

Myth 1: An object always moves in the direction of the net force exerted on it.

If an object always moves in the direction of the net force exerted on it, and we roll a bowling ball across a level carpet surface with friction acting against the ball, then the bowling ball will continue to move in the same direction that it was originally travelling in.

Our procedure for myth one was simple: Roll the bowling ball across the carpet surface.

The small arrow represents the direction of motion.

ΣFx = -Ff

ΣFy= Fn-Fg

The ball is not moving in the way the only horizontal force, friction, is being applied to it.  It still moves to the right, when the force of friction is moving to the left, so the myth is busted!

Myth 2: An object always changes its motion if there is a force exerted on it by other objects.

If an object always changes its motion if there is a force exerted on it by other objects and we swing a tennis ball into a bowling ball while in motion, the bowling ball's path/direction it is going in will not be affected.

Procedure:

1.   Suspend tennis ball from the ceiling with a piece of string.

2.  Hold tennis ball in air while still attached to string.

3.  Roll bowling ball into tennis ball's path.

4.  Release tennis ball from hand, allowing it to swing directly into the bowling ball while it is moving.

 

The small arrow represents direction of motion.

ΣFx = -Fa

ΣFy = Fn-Fg

The ball is moving to the right, but the only force (the applied force of the tennis ball) is moving to the left.  Even though the bowling ball has a left force pushing on it, it is not strong enough to change the direction of the already moving bowling ball (going to the right).  Busted!

CONCLUSION:

We ended up disproving both myths.  But even if we hadn't disproved both, the myth still wouldn't have been proven because we wouldn't have tried every experiment/lab possible.  People believe myth one is true because most people assume the object being forced upon is starting at rest.  For example, a ball at rest gets hit by a foot.  The ball resultantly moves in the same direction as the foot was when it hit the ball.  Most people don't even consider or think about smaller forces like friction.  Because the bowling ball already had enough speed/momentum, the friction acting in the opposite direction did not have any effect on the bowling ball's direction.  People usually believe myth two is correct because they automatically assume the opposing force is stronger than the original object, which is not true in many cases.  For example, in our experiment, the tennis ball had much less force than the moving bowling ball, so the bowling ball's path was not affected at all by the strike of the tennis ball.  Both myths were BUSTED!!!