When two lumps of soft clay collide head-on and stick together, coming to a complete stop with no visible flash, sound, or motion afterward, where did all the kinetic energy go, if energy is supposed to be conserved?
#mechanics
Post a problemWhy does the free end of a chain falling off a table, or piling onto the floor, accelerate downward faster than gravity alone (g) would predict?
Why do structurally similar knots differ enormously in the force needed to make a rope slip or break, and can this be predicted?
What actually keeps a riderless bicycle rolling straight and stable without falling over?
How can a small spinning magnetic top hover stably in midair above a magnetic base despite Earnshaw's theorem forbidding static magnetic levitation?
How can a cat dropped upside-down with zero angular momentum twist itself around in mid-air to land feet-first, without violating conservation of angular momentum?
Why does a boomerang thrown correctly curve around and return to the thrower instead of flying straight?
Can a wind-powered vehicle sail directly downwind faster than the wind itself, and if so, how?
Why does a curling stone curve in the direction it is spinning, when simple friction models predict it should curl the opposite way or not curl at all?
How can a snake, with no legs, generate enough forward thrust on flat ground to move forward using lateral undulation alone?
Why does an arrow that appears aimed to the side of the target (because it must flex around the bow at release) actually fly straight to the target?
By alternately standing/squatting or rocking your body on a swing with no one pushing, you can increase the swing's amplitude: what is the physical mechanism, and is it a driven or a parametric oscillator?
The 1908 Tunguska event released energy equivalent to a very large meteorite impact: could an object of that scale have measurably changed the length of Earth's day or its axis of rotation?
When a whip is snapped, why does its tip produce a sharp crack loud enough to sound like a gunshot, and what makes the tip move fast enough to cause it?
If you hold a stretched Slinky vertically and let go of the top, why does the bottom of the Slinky stay completely still, floating in place, until the collapsing coils above reach it?
Why does a properly thrown boomerang travel out in a curve and return to the person who threw it, instead of flying in a straight line like any other thrown object?
How can a cat dropped upside-down with zero initial spin still rotate itself in mid-air to land on its feet, given that it starts with zero angular momentum and nothing to push against?
When a spinning coin or disk settles flat on a table, why does the frequency of its wobbling/rattling sound rise dramatically just before it comes to rest, instead of dying away smoothly?
Why does a Superball thrown with backspin straight down sometimes bounce back toward the thrower instead of continuing forward, and why does its spin direction reverse after the bounce?
If you strike a free rigid rod with a sharp blow at one point, why does a particular other point on the rod feel almost no jolt at all, while striking closer to that point makes your hand sting badly, as if the rod 'chooses' where to react?