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Question 9: Explain the warning, ‘never use a long wrench to tighten a small bolt’.


When we tighten (or loosen) a bolt with a wrench, we in fact apply a torque on the bolt. Now we know the torque is proportional to the moment arm. Mathematical equation for the magnitude of torque is

Here r is the moment arm.

For a large wrench, the moment arm is larger and therefore, a greater torque is produced. If we use such a large wrench for tightening a small bolt, a large torque will produce. This may damage or break the bolt.


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