* Instantaneous speed is a specific value at a specific moment in time. Think of it like looking at the speedometer in your car. It shows you how fast you're going *right now*.

* If an object's instantaneous speed is constant, that means its speed isn't changing at that exact moment.

However, the question is asking what *doesn't change* an object's motion, and instantaneous speed alone doesn't tell us that.

Here's what influences an object's motion:

* Velocity: This includes both speed *and* direction. If the object's direction changes, even if its speed stays the same, its velocity changes.

* Acceleration: This is the rate of change of velocity. So, even if the object's speed stays constant, if its direction is changing, it's accelerating.

So, to answer the question directly: A constant instantaneous speed doesn't guarantee that an object's motion *won't* change. It only means that the speed isn't changing *at that specific instant*.