which of the following refers to the motion of an object falling straight down with only the force of gravity acting on it

Since you haven't provided any choices, then the answer is "Free Fall Motion."

Explanation:

In order to learn more about the answer, let's discuss what free fall motion is.

Free Fall - In Physics, this refers to any body motion that is acted upon solely by "gravity." The acceleration in free fall is always downward and there's the absence of other forces. Take note that the acceleration should be the same and is independent of the object's mass. This acceleration is called "acceleration due to gravity."

Gravity - This refers to the force that pulls any object towards the center of the earth.

Examples of Objects in Free Fall Motion

1. A ball dropped at the top of a building.

2. Dropping a coin from a table.

The ball and the coin are both in free fall motion because they are being pulled by gravity towards the earth. Their acceleration is also constant and there are no other forces acting upon them.