Can anyone help me on a physics problem?

Seeing as acceleration is the change in velocity over time, anything with NO force acted upon it would NOT be acceleration. Moving in a straight line at a constant speed means that it would be encountering Gravitational forces and Air Friction, which both in turn would mean the object would have to keep Accelerating to stay constant. Moving on a turn is the same principal, it has to accelerate to keep the object in a uniform circle. Moving in a gravitational field with no air resistance means that no acceleration would occur, due to no friction.