The Physics of Bullying

A friend recently gave me a heads up that they found a picture of me online. Unfortunately, when I went to investigate, all I found was an embarrassing picture of me being punched. By Richard Chang, no less~~ (shame!). I never wanted my brief incidence of e-fame to be so violent!




I fondly remember this incident where his fist navigated squarely to my stomach. While wallowing in pain, I immediately saw the PHYSICS of my misfortune:

Impulse is defined as the change in momentum. Assuming that Richard's fist has a mass of .5 kg, an initial velocity of 5 m/s and a final velocity of 0 m/s, I calculated the change in momentum of Richard's fist. Note that final momentum is zero due to final velocity being zero, so change in momentum is simply equal to (negative) initial momentum.

mv = (.5)(5)=2.5 kg x m / s

0 kg m/s - 2.5 kg m /s = -2.5 m/s

Another variable we've used many times is the quotient of impulse and time, average force. Given the time of contact, say, 0.3 seconds, I can calculate exactly how pissed off Richard was (how much force he used in his punch).

F(average) = changeMomentum (Impulse)/changeTime

F(average)=-2.5/0.3 ~ -8.33 Newtons

Since Force is a vector, it has consequently magnitude and direction. Richard's fist can have a negative component along a coordinate axis, but having a negative magnitude makes no sense. Therefore, Richard's force was approximately 8 (positive) Newtons.

On a different note, I was asked to exclude John McCain from any future blogs. Sorry.