Look at smoke under a microscope and the bright specks dance about in tiny, random zig-zags. Nothing visible is pushing them. That restless jiggle is the first direct hint that matter is built from countless fast moving particles too small to see.
Brownian motion is the random, jerky movement of small visible particles suspended in a fluid. It happens because they are constantly struck, unevenly, by the much smaller and faster moving molecules of the fluid around them.
Brownian motion is the random movement of small particles suspended in a liquid or gas, caused by collisions with the fast-moving molecules of that fluid.
The bombarding molecules are smaller and faster than the particle you can see.
Watch a large visible grain being knocked about by the unseen molecules of the fluid.
Four quick checks. Each correct answer earns XP and lights this skill on your star map.
Brownian motion is the random motion of...
The jerky movement of a smoke particle is caused by...
Brownian motion provides evidence that...
The molecules that bombard the visible grain are...
The motion you can see is indirect evidence for the molecules you cannot.
The visible grain is not moving under its own power. It is pushed around by the unseen molecules, and because the collisions arrive unevenly from all sides, the resulting path is random rather than smooth.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.
In a smoke cell viewed under a microscope, the bright specks seen moving randomly are...
A pollen grain on water jitters about because the water molecules...
The Brownian motion of smoke grains becomes more vigorous when the gas is...
Another particle-model skill secured. Keep the chain going.