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Experiment: Pure twist (Repeat)

If you use a spanner to undo a nut, the twist you generate comes from the force you apply.

This experiment appeared in Week 3. We have repeated it here because we will use our new analytical skills to get a deeper understanding of the concept of a couple – that is, pure twist.

Remember, if you use a spanner to undo a nut, the twist you generate comes from the force you apply.

The twist and the force come as a package.

If you use a screwdriver to undo a screw, the twisting effect comes without a net force (apart from the force along the axis to keep the blade in place, but that’s another story).

Two parallel, equal, opposite forces generate twist without unbalanced force. This is a ‘couple’ or ‘couple moment’. It has many applications in engineering mechanics.

Talking points

  • Was it difficult to understand this the first time around?
  • Do you still think the mechanism is elegant, see what you think? (Robin Ford)

Share your experiment

If you attempt the experiment, take a photo and upload it to our Through Engineers’ Eyes Padlet wall. You can include a link to your photo in the comments for this step (click on your post on the Padlet wall and then copy the web address).

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Through Engineers' Eyes - Introducing the Vision: Engineering Mechanics by Experiment, Analysis and Design

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