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Tilting (OCR A Level Maths: Mechanics)
Revision Note
Tilting
What does it mean if a rod is on the point of tilting?
- A rod will tilt (rotate) about a pivot if the resultant moment about that pivot is non-zero
- Examples of tilting:
- A person walking a plank on a ship will get to a certain distance before the plank tilts
- Children playing on a seesaw
How do I solve problems involving a rod on the point of tilting?
- If a rod is on the point of tilting about a pivot (at a support) then the reaction forces at the other supports are zero
- The rod is still in equilibrium at the point of tilting
- Taking moments about the pivot is the key step as it allows you to ignore the reaction force
- The question might not use the phrase “tilting”
- It could ask you how far along a plank that it is safe to walk (it is safe as long as the plank does not tilt)
- It could ask you to find the maximum mass that could be hung from a rod that would keep it horizontal (as soon as it begins to tilt it is no longer horizontal)
Worked example
Examiner Tip
- Remember to use common sense! If a rod was supported by two supports and a mass was placed on the rod in between these supports then the rod would never tilt (in real-life it might break though).
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