kilogram square meter per second

Angular momentum in kg·m²/s is the conserved quantity of everything that spins, and the scale runs enormous. A figure skater in a fast spin carries a few tens of kg·m²/s, which is why pulling the arms in visibly speeds the spin: the product of moment of inertia and angular velocity cannot change, so shrinking one grows the other. The Earth's daily rotation carries about $7 \times 10^{33}$ kg·m²/s, and that number is not quite constant.

The best evidence is the Moon. Tidal friction slowly brakes the Earth's spin, and conservation demands the lost angular momentum go somewhere: it transfers into the Moon's orbit, which must therefore widen. Lunar laser ranging against the retroreflectors left by the Apollo missions measures the recession directly, about 3.8 centimetres per year, one of the few conservation-law consequences you can watch accumulate with a ruler. The day lengthens by roughly 2 milliseconds per century for the same reason.

Spacecraft engineering uses the identical unit under a different spelling. Reaction wheels, the flywheels that point telescopes and satellites without burning propellant, are specified by their momentum storage in newton metre seconds, and $\mathrm{N\,m\,s}$ is exactly kg·m²/s. When the wheels saturate, the accumulated angular momentum has to be dumped through thrusters or magnetic torquers, a routine housekeeping chore driven entirely by this quantity's refusal to disappear.