lesson 4.2 Torque - Torque According to the second law for...

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Torque According to the second law for linear motion, linear acceleration a is caused by a net force F net . The second law is equally applicable to rotational motion. Rotational acceleration α is caused by a torque ( τ ) A force F applied at right angles to the handle of the screw produces a rotation on the screw about an axis through its center. The perpendicular distance between the force F and the axis of rotation is r F Axis of rotation r 1
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F r The torque τ produced by the force F about the axis of rotation is: τ = r · F r is called the torque arm. r is a vector drawn from the axis of rotation to the point of application of the force. If the force F makes an angle θ with the vector r , the torque is produced by the component of F at right angles to r , θ F The component of F at right angles to r is F sin θ F sin θ Torque of F about the axis in this case is: τ = r · F sin θ τ is measured in m·N 2
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The product of a vector and the component of another vector at right angles to it is called the cross product of the two vectors. r · F sin θ is the cross product of the vectors r and F Cross product of two vectors is a vector at right angles to both vectors. τ = r x F. r r x F τ is a vector at right angles to both r and F The direction of τ is given by the right hand rule. Keeping the thumb at right angle to four fingers, wrap the four fingers from r to F . The thumb will indicate the direction of τ 3
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r 30o 4
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The figure shows a crowbar used to remove a counter top. The workman applies a 50 N force vertically down at a point 60 cm from the fulcrum of the crowbar, find the torque produced by the force about the fulcrum. The crowbar makes an angle 30 o with the vertical.
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lesson 4.2 Torque - Torque According to the second law for...

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