1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Using watts to help determine velocity?

  1. Feb 18, 2009 #1
    Here's what I know about an abstract object:
    *mass
    *position
    *all external forces acting upon it (gravity ;)
    *that it is exerting force upon itself
    *direction of said force
    *number of joules per second being used in said force (watts)

    Can I use these to determine the velocity of the object? If not, what other information do I need? It's important that the joules per second (watts) be a part of the equation.
     
  2. jcsd
  3. Feb 18, 2009 #2
    as long as you can find a resultant force acting in one direction, you can calculate the velocity from the force and the power using P=F*v Power=Force*Velocity
     
  4. Feb 18, 2009 #3
    Re: using watts to help determine force?

    Well, then, maybe this is a better question. Can you determine force from watts (joules per second) expended producing said force?
     
  5. Feb 18, 2009 #4

    LowlyPion

    User Avatar
    Homework Helper

    I think since velocity is the rate of change of position with respect to time, that without knowing some rate of change in position, as an initial condition, and the history of forces and energies affecting the object since, then you can't just tell from knowing all the forces acting on it at an arbitrary moment, because those forces result in accelerations, and those accelerations are only the rate of change of velocity at some point and don't necessarily speak to what it may be changing from or to.

    I think you need to know it was at rest somewhere, or its velocity somewhere, and its history since to be able to determine what it's total kinetic energy (and hence velocity) is at the point of interest.
     
  6. Feb 18, 2009 #5

    LowlyPion

    User Avatar
    Homework Helper

    Re: using watts to help determine force?

    J/s if you know the duration gives you joules and joules gives you energy added to the object and hence you know how much its kinetic energy may have changed.

    But in reference to the prior post you only know how much it may have changed, and without knowing what it's kinetic energy is initially, then ...
     
  7. Feb 18, 2009 #6
    I'm doing a simulation. That's why I need this info. I forgot to mention that the object begins at rest. However, the simulation is not in Earth's gravity. It is in a theoretical space without any major gravitational influence.
     
  8. Feb 18, 2009 #7

    LowlyPion

    User Avatar
    Homework Helper

    Well in that case yes.

    You have position and it's at rest then all you need then is the forces and durations over its history to the moment of interest I'd say.
     
  9. Feb 19, 2009 #8
    So, what is the equation to figure out force using joules per second?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook