What on earth stays at a constant speed?

Answer 1

nothing, the reason i say this is because the earth is moving at a pretty much constant speed, therefore everything at rest on earth is also moving at a constant speed, however remember i said "pretty much" constant, actually the earth is slowing down (- acceleration, not constant speed); Case1 (macro): so for something on earth to be and stay at a constant speed it would need to be moving against the rotation of the earth at the same exact rate at which the earth is de-accelerating (which is highly unlikely because the prescision needs to be 100%) or something in the air could travel at a constant rate (but again highly unliky due to gravity, which changes/adds to the acceleration of a system and/or due to the propulsion "system" of the system (changing engine(mech(jet/plane) or bio(wings/muscles)) output)). Case2 (micro) since most subatomic particles' motions are related to the temperature, which is usually continuosly changing, their speeds are usually changing. Light changes speeds as it passes through different mediums in the atmoshpere, cosmic particles/waves +/-accelerate as they approach the ground/change mediums.

So in conclusion, im pretty shure its nothing! your best bet is to find something on the microscale which always moves at a constant rate.

Also the part of the question "stays" is interpretable

Answer 2

Objects in motion can stay at a constant speed if the net force acting on them is zero. This can occur in scenarios like an object moving at aconstant velocity through space or an object in freefall under the influence of gravity.