Final answer:
The acceleration of an object moving in a straight line refers to the change in velocity, in terms of speed and/or direction. It is calculated by dividing the change in velocity by the time interval over which it occurs, and it is a vector quantity.
Step-by-step explanation:
The definition of acceleration of an object moving in a straight line is a change in velocity, which includes changes in its magnitude or direction, or both. Acceleration is considered a vector quantity, meaning it has both magnitude and a direction. The average acceleration can be calculated when we have a change in velocity (Δv) over a time interval (Δt), with it being the rate of change of velocity. In instances of uniform circular motion, the direction of the velocity changes constantly, leading to continuous acceleration, known as centripetal acceleration, despite the velocity's magnitude remaining constant. Moreover, instantaneous acceleration is determined by taking the derivative of the velocity function with respect to time. Lastly, in situations where we talk about projectile motion, we deal with an object subject only to the acceleration due to gravity, which typically involves constant acceleration near the Earth's surface.