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lecture 17

# lecture 17 - Lecture 17 Torque Rotational form of Newton's...

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1 Lecture 17 Torque Rotational form of Newton’s 2 nd law

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2 A body can be set in rotational motion by the action of a torque. A rotating (spinning) body will continue to rotate unless it is acted upon by a torque. hinge P u s h Q: Where on a door do you push to open it? A: Far from the hinge.
3 Torque F r τ × = Torque is a vector. It’s magnitude is θ sin rF τ = It’s direction is found from a right-hand rule: point your fingers in the direction of r and curl them into the direction of F . Your thumb will point in the direction of the torque.

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4 Torque method 1: = rF τ Hinge end F F || F θ r = the distance from the rotation axis (hinge) to the point where the force F is applied. F is the component of the force F that is perpendicular to the door (here it is Fsin θ ). Top view of door
5 The units of torque are Nm (not joules!). By convention: When the applied force causes the object to rotate CCW then τ is positive When the applied force causes the object to rotate CW then τ is negative

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6 Torque method 2: F r = τ r is called the lever arm and F is magnitude of the applied force.
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