A tilted tray: when does the salt shaker slide
Identical salt shakers stand on trays tilted 10°, 20° and 35°. Find the angle where static friction no longer holds.
2D
Age 8+10 min
FrictionGravity
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Press “Run”. Bodies move by the laws of physics: gravity, friction, elasticity.
What the experiment shows
While the tray is only slightly tilted, static friction holds the shaker. As the angle grows the downhill force grows and the pressing force shrinks — at some point the shaker slips.
How to run it
- Press “Run”: which shaker slid?
- In the editor turn the middle tray to 25° and test again.
- Find the slipping angle to the nearest degree.
Questions to discuss
- How does the slipping angle tell you the friction coefficient?
- Does the angle depend on the shaker’s mass?
The science
A body starts to slide when tan α exceeds the static friction coefficient μ. Mass cancels out: the slipping angle depends only on the surfaces. For μ = 0.4 it is about 22°.
Try it at home
Put an eraser on a book and slowly lift one edge. Measure the angle with a protractor when it slips.
What to change in the editor
- Make one shaker rubber (friction 1).
- Lay a shaker on its side.