Why is acceleration of an object moving at a constant velocity always zero?

If an object is moving with a constant velocity, then by definition it has zero acceleration. So there is no net force acting on the object. The total work done on the object is thus 0 (that's not to say that there isn't work done by individual forces on the object, but the sum is 0 ).

Explanation:

In the middle, when the object was changing position at a constant velocity, the acceleration was 0. This is because the object is no longer changing its velocity and is moving at a constant rate.

when heated, the valance electrons increased their speed and transferred the heat from electron to electron.   i just took the test.