How far can a stack of identical bricks, each balanced on the one below it, be made to overhang the edge of a table before it topples — is there any theoretical limit to how far the top brick can stick out?
#mechanics
Post a problemWhy can burning the same amount of fuel to give a rocket the same boost in speed release far more kinetic energy when the rocket is already moving fast than when it starts from rest — seemingly getting extra energy for free?
The Gomboc: does a self-righting convex body with just one stable and one unstable point exist
Research level
Does a convex, uniformly dense three-dimensional shape exist that always rights itself to the same single stable resting position, like a roly-poly toy but with no internal weighting?
How does a hula hoop stay up against gravity?
Research level
As you gyrate your hips, why does a hula hoop rise and stay suspended around your waist instead of falling to the ground, and what shape of body is required for this to work at all?
A moving bicycle with no rider steering it can recover from being pushed sideways and keep rolling upright by itself: what physical effect makes it self-stabilize?
Can a wind-driven vehicle sail directly downwind, or even upwind, faster than the wind itself?
Research level
If a ship's propeller is driven by a wind-turbine-like air motor connected to the wheels or propeller, can such a vehicle move faster than the wind, including directly against it?
Why did the newly opened Millennium footbridge in London begin swaying alarmingly from side to side as soon as a crowd walked across it, even though it had been engineered to withstand pedestrian loads?