Popcorn

This is a picture of me (courtesy of Tiffany :)) attempting to throw a popcorn into the trash can in the physics classroom. (This picture was actually taken after the fact, but that is besides the point.) On Monday afternoon, Richard, Christina, Trisha and me were sitting in Doc's room doing physics and PCH homework while enjoying a nice bowl of popcorn. Unfortunately, I dropped a single popcorn on the ground. Because everyone at school has recently been getting sick, I decided not to eat the fallen kernel. I admit that I am a lazy person, so of course I did not want to walk all the way to the trash can. Instead, I got up and attempted to throw the popcorn into the trash. But alas, the kernel didn't even made it halfway to the targeted can! The reason for this is physics! More specifically, air resistance. We all know what air resistance is, and according to our book it is, "A force that opposes motion in air." Air resistance occurs because when an object moves through the air, it collides with the molecules that make up the atmosphere. Air is not very dense and the molecules are very small, but there are a great deal of them so all together, it results in a pretty big force, which we call air resistance.

One major reason why the kernel didn't make it into the trash can is because of surface area. The kernel had a relatively large surface area, meaning that it collided with more air molecules resulting in a relatively large air resistance. In addition, the kernel had a relatively small mass. The air resistance force itself does not vary with mass, but the effect of air resistance does.

Now for some general background on air resistance: Air resistance is not constant. Instead, it is proportional to the speed of the object. The force created by air resistance is called drag. You can use the equation: FD = 1/2 CpAv^2 to find the drag force, where C = drag coefficient for object, p = air density, A = cross-sectional area, and v = velocity. The shape of an object as well as significant changes in speed determine the drag coefficient. From this equation, you can see what factors determine the drag force on an object.

I guess from now on, I'll have to get up and walk all the way to the trash can when I drop popcorn on the floor, which is inevitable since I am a fairly messy eater.