One equals TwoDate: 07/25/2001 at 17:36:12 From: Dick Subject: One equals Two There is an algebraic manipulation involving division by zero that results in one equals two, or some other contradiction. What is it? This is a physics "proof" that one equals two. Proof That One Equals Two Beginning with the well known equations for uniform motion: s = 1/2(a)t^2 and solving each for acceleration, a : a = v/t and a = 2(s)/t^2 and setting them equal to each other: v/t = 2(s)/t^2 And using the fact that s = vt and substituting: v/t = 2(v/t) Thus factoring each side by v/t: 1 = 2 Ta Da! Date: 07/25/2001 at 22:56:23 From: Doctor Peterson Subject: Re: One equals Two Hi, Dick. We have a FAQ that gives several of these false proofs: False Proofs, Classic Fallacies http://mathforum.org/dr.math/faq/faq.false.proof.html You are probably aware that the main use of such fallacies is to teach us the dangers of unthinking manipulation of equations. That is just as important in physics as in math. In your physics "proof," the problem is that you are using formulas that apply to different situations. The first two apply to the same falling body, at a fixed time t after being dropped (or exposed to a force), which results in velocity increasing from zero. But s = vt applies to a constant velocity, not a constant acceleration. And in fact, under constant acceleration, the average velocity happens to be just half of the instantaneous velocity, which accounts for the ratio of 1:2 you found. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
Search the Dr. Math Library: |
[Privacy Policy] [Terms of Use]
Ask Dr. Math^{TM}
© 1994-2015 The Math Forum
http://mathforum.org/dr.math/