Looking at our equation for torque, we see that it only depends on the size of the force and the lever arm. The torques due to the bicep tension and the ball weight are trying to rotate the elbow in opposite directions, so if the forearm is in static equilibrium the two torques are equal in size they will cancel out and the net torque will be zero. Writing these conditions on the torque and force in symbol form we have: In symbol form it looks like this:įor an object to be in static equilibrium both the equilibrium conditions must be met. Image adapted from Openstax University Physics.įinally, we can calculate the torque by multiplying the size of the force by the length of the lever arm ( ) and that’s it, you get the torque. ![]() We can draw these lines for our example problem: Diagram of the flexed arm showing the line of action of the gravitational force and the perpendicular distance from the pivot to the line of action. The perpendicular distance is also sometimes called the lever arm or moment arm or torque arm. This shortest line and the line of action of the force will always be at 90 ° to each other, so the shortest line is called the perpendicular distance ( ). Next you draw the shortest line that you can from the pivot point to the line of action of the force. One method to account for the effect of the distance to pivot when calculating the size of a torque you can first draw the line of action of the force, which just means to extend a line from both ends of the force arrow ( vector) in both directions. Does the door open as easily as before, or did you have to push with greater force to make the door rotate? Now apply the same force perpendicular to the door, but right next to the hinges. Open a door by pushing perpendicular to the door near the handle, which is far from the pivot point at the hinges. To feel this effect for yourself, try this: ![]() The torque caused by a force depends on the distance that force acts from the pivot point.
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