1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Torque on a hammer conceptual question.

  1. Nov 15, 2012 #1
    1. The problem statement, all variables and given/known data

    If you are trying to loosen a stubborn screw from a piece
    of wood with a screwdriver and fail, should you find a screwdriver for which
    the handle is (a) longer or (b) fatter?

    2. Relevant equations

    [itex]\tau[/itex] = r * F * sin([itex]\theta[/itex])

    3. The attempt at a solution

    I guessed longer because i figured that the larger radius would mean that you have a larger torque and need less force than if the radius was short, however the correct answer is B. Can someone explain this to me please?
  2. jcsd
  3. Nov 15, 2012 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Larger torque, yes, but you don't get that from a longer screwdriver.
    When using a given screwdriver, the limiting factor is the tangential force you can apply around the handle. That in turn is limited by the torque you can exert from your arm, but more often it is limited before that by the static frictional force achieved by your grip (as the normal force) on the handle.
    What equation would relate such a tangential force to the resultant torque?
    (The free body diagram might look unlike anything you're familiar with. If it helps, consider the tangential force as lots of little forces scattered around the handle.)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook