Here's how acceleration changes when total mass increases but the unbalanced force remains constant:

The acceleration decreases.

Explanation:

Newton's Second Law of Motion states:

* Force (F) = Mass (m) x Acceleration (a)

This means:

* Acceleration (a) = Force (F) / Mass (m)

If the force remains constant, and the mass increases, the denominator in the equation becomes larger. Therefore, the resulting acceleration will become smaller.

In simpler terms:

Imagine pushing a small cart with a certain force. It accelerates quickly. Now imagine pushing a much heavier cart with the same force. The heavier cart will accelerate much more slowly. This is because the greater mass resists the change in motion.