#mechanics

Why does a chain of beads poured out of a beaker rise up in an arc above the rim before falling, as if pulled up by an invisible force?

What determines the characteristic drooping, fanned-out shape of a bundle of hair such as a ponytail?

Why does a dry rod of spaghetti bent until it snaps almost always fragment into three or more pieces instead of two?

What part of a whip actually produces the crack sound, and is it really breaking the sound barrier?

Why does a hard-boiled egg spun fast enough on a table rise up and spin on its end?

Why does a spun coin or disk settling flat on a table spin faster and faster, with the clatter rising in pitch, right up to the instant it stops?

Why does a rattleback (celt) toy spin smoothly in one direction but wobble and reverse its spin when started the other way?

Why does a spun tippe top (a truncated-sphere spinning toy) flip over and spin balanced on its stem instead of its round base?

Is it really true that dropped buttered toast is more likely to land butter-side down, and if so why?

When you hold a stretched Slinky vertically and let go of the top, why does the bottom of the Slinky stay hanging motionless in mid-air until the collapsing coils reach it?

Is it really impossible to fold a piece of paper in half more than about 7 or 8 times, and what determines the true limit?

For a coin or plate spinning and wobbling flat on a table, why is the wobble (precession) frequency exactly twice the spin frequency in the small-angle limit?

What determines the propagation speed of a wave of toppling dominoes, and why does it approach a roughly constant value regardless of how hard the first domino was pushed?

Given a single strand of curly hair's intrinsic curvature, what determines the diameter of the curls it forms under its own weight?

Why does everyone naturally switch from walking to running at close to the same critical speed relative to their leg length?

Why, when a container of mixed different-sized granular particles (like nuts or cereal) is shaken, do the largest particles reliably rise to the top rather than settling based on density?

Achilles, though ten times faster than a tortoise with a head start, seems logically unable to ever catch it, since by the time he reaches where the tortoise was, it has always moved a little further ahead.

When several bodies move relative to one another (e.g., a person walking inside a moving train, or a boat crossing a flowing river), why does naively adding or subtracting the given speeds as plain numbers often give an obviously wrong resulting speed or direction?

If you travel the first half of a trip's distance at 60 km/h and the second half at 30 km/h, is your average speed for the whole trip the simple arithmetic mean, 45 km/h?

Inside an accelerating vehicle, a ball resting on a frictionless floor suddenly starts rolling backward even though nothing visibly pushes it — apparently violating Newton's first law that a body at rest stays at rest unless acted on by a force.