Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Conservation of Energy

  1. Nov 11, 2014 #1
    So negatives always get me, no matter what and I'm having a hard time understanding the conservation of energy. Anywho, I'll continue. In a system, oh let's say a block on a rough surface with some intitial v and kinetic energy K at point A. After it gets to B, friction has done W amount of work on the block and now it has velocity ϑ and kinetic energy k. Consequently, K=k+W, so work by friction would be W=K-k, but then that means, algebraically, W is positive if the block is moving to the right. Friction always works against an object's velocity so the work is actually -W. Why doesn't the algebra show this? What am I missing?
     
  2. jcsd
  3. Nov 11, 2014 #2
    The energy dissipated by work is defined as [itex] E_f-E_i = W[/itex] and it's clearly negative. You are simply writing it in the other way. It should be k-K=W and so k = K+W. This just means that the final kinetic energy is smaller than the initial one (remember that W<0) because of dissipation.
     
  4. Nov 11, 2014 #3
    Well that makes sense. I was just reading it wrong. Thank you!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Conservation of Energy
  1. Conservation of Energy (Replies: 6)

  2. Conservation of energy (Replies: 3)

  3. Conservation of Energy? (Replies: 15)

  4. Conservation of Energy (Replies: 5)

Loading...