For this lab, we were put into teams and try to disprove two myths involving physics. We had to film ourselves doing this and make into into a Mythbusters show. My team consisted of myself, who served as the person who does what everyone tells her to do in order for the show to take off; Cara, one girl camera crew extraordinaire; Ryan, who operated the "man-coaster"and the bowling ball (for all of you who are wondering what a man-coaster is, it will all become clear in the video); and finally Adam, who helped. It was a thrilling and dangerous venture, but it was all worth it in the end, because we all learned what only phsicists could- how to bust a physics myth.
MYTH #1:
An object always moves in the direction of the net force exerted on it.
This seems that's it's correct right? I mean, look at yourself when you push a grocery cart - where is it going? In the direction of the net force exerted on it, the positive direction. So, you think, Don't all things work the same way?
WRONG! If you think this you are making the same mistake that many others have made before you. I mean, look what my teammates and I did. We put Ryan on a rolling board that we dubbed the "man-coaster" and we pushed him for a second, then let go and watched him roll. Once we took our hands off of him, the was no force acting on him in the positive direction- his direction of motion. However there was friction acting against him and his man-coaster. According to the myth, he should have started moving in the negative direction, or backwards. But he didn't, he kept going forward until he stopped. Don't believe me? Take a look at the FBD I have made for you.
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As you can see, the FBD shows how our experiment busted the myth, as Ryan continued moving in the positive direction even though the net force was in the negative direction! This is the equation of the net force:  |
An object always changes its motion if there is a force exerted on it by other objects.
Well duh! you are probably thinking as you read this myth. You think about if a soccer ball is rolling toward you, and you kick it, it will change direction, right? So why shouldn't this always be true? Well once again, my Mythbustin' team and I are here to tell you that sometimes this statement is false! Just ask the classroom full of fourth graders that stood to the side of the hallway as Ryan used his bowling skills to hurl the ball onto the ground and roll it past me. I waited off to the side to ambush the ball with a highlighter, throwing it at the ball and promptly bouncing off the bowling ball and not altering its direction at all. Myth busted! The highlighter was too light to change the heavy bowling ball's direction, but it was a force never the less.
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There were no myths that my team could not disprove. However, at first sight, these myths make you do a double take because, really, you don't know why it's a myth in the first place, because it seems right. Maybe people believe these myths because once they read them, it's hard not to think about examples that only support them. The examples I gave when describing the myth as to why you might doubt that it's false are exactly the type of examples that people think of when they read the statement. You only find out a way to disprove the myth when you actually start trying things out, and that's why I think people believe these physics myths.
