Statics › Section I · Friction › Topic I.4
Screw threads
A car jack lets one person lift the corner of a car, and a vice can crush wood with a turn of the handle. Both are screws: inclined planes wrapped into a helix, where friction decides how hard they are to turn and whether they hold their load on their own.
In this topic
- A wedge wrapped round a cylinder
- Handedness and the right-hand rule
- Thread geometry
- Raising a load
- Lowering a load: three cases
- Worked example: a screw jack
- Efficiency and the price of holding
- Worked example: a two-start lead screw
- Common mistakes to avoid
- Key takeaways
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