A bird is flying south at 20 mph. Then the bird turns to go west. The bird is still flying at 20 mph. Did the velocity change?
The Correct Answer and Explanation is:
Yes, the velocity did change.
Explanation
Velocity is a vector quantity, which means it includes both magnitude (speed) and direction. In this problem, the bird maintains a constant speed of 20 miles per hour (mph), but it changes direction — from south to west. Since velocity depends on both speed and direction, changing either one results in a change in velocity.
Let’s examine this in more detail.
Initially, the bird is flying south at 20 mph. Its velocity vector points directly toward the south. When the bird turns to fly west at the same speed, the magnitude of the velocity (20 mph) remains the same, but the direction of the velocity vector shifts 90 degrees — now pointing west. This change in direction alters the velocity vector entirely, even though the numerical speed is unchanged.
This situation can be compared to walking at the same pace but turning a corner. Even if you don’t slow down or speed up, your path — and therefore your velocity — is different. Because direction is a fundamental part of velocity, any change in direction results in a different velocity.
This concept is especially important in physics. For example, acceleration is defined as the rate of change of velocity. In this case, even though the bird’s speed is constant, it is undergoing a form of acceleration called centripetal acceleration, due to the change in direction. So, turning from south to west means the bird accelerates — not by going faster, but by changing direction.
In conclusion, the bird’s velocity did change, because while the speed remained constant, the direction did not. Any alteration in the direction of motion means the velocity has changed, affirming that velocity is not just about how fast something moves, but also in what direction it moves.
