Why is it that an object can accelerate while traveling at constant speed, but not at constant velocity?

here's a good explanation of it https://www.quora.com/Why-can-a-car-accelerate-while-traveling-at-a-constant-speed-but-not-at-constant-velocity

the earths atmosphere is made up of nitrogen and oxygen. solids can turn into gasses through a process called sublimation. sublimation is the transition of a substance directly from the solid to the gas phase, without passing through the intermediate liquid phase.

hope this : d