Friday, December 2, 2011

The Physics of Slipping on a Banana Peel

Friction is an important concept
-less friction = more slippery
-To slip on a banana peel, the force of linear velocity must overcome downward static friction
-Once you start to slip, it is difficult to stop because kinetic friction is less than static

Newton's 1st Law of Motion at work here
-Definition: an object in motion will stay in motion unless acted on by an outside force

We also see Newton's 3rd Law of Motion
-Definition: for every action there is an equal and opposite reaction
-When you slip, there is an accelerated force forward
-In response, there is a backwards force on your body which can cause you to fall

Mythbusters conducted an experiment examining this concept.

Hypothesis #1: A banana peel on the ground is guaranteed to cause the person who steps on it to slip and fall. BUSTED. In their first test, a blindfolded Jamie (wearing body protection) stepped on a banana peel while walking, but did not slip. In the second test, multiple banana peels were laid down in Jamie’s path, but he did not slip. He then tried running through the banana peels but still failed to slip. They performed further tests by measuring a banana peel’s static friction and kinetic friction and comparing it to lubricant, with the lubricant having far less kinetic friction but the banana peel having somewhat less static friction. In their full scale test, the MythBusters built a race course that had the entire ground covered with banana peels, and later lubricant. They compared how quickly and easily they could negotiate the course with banana peels and the lubricant, doing comically poorly in both cases. In the end, they found that banana peels would not guarantee a fall but could still prove to be very slippery on a smooth enough surface.

Their conclusion?
-Bananas are slippery, but slipping on a banana peel is unlikely due to the strong static friction between a shoe and the tough outside skin of the peel
-In their experiments, the individual only fell when multiple bananas and lubricant were on the ground

Here is the experiment: