Here's why:
* Speed is a scalar quantity, meaning it only has magnitude (how fast something is moving).
* Velocity is a vector quantity, meaning it has both magnitude and direction.
If an object moves in a straight line without changing direction, its velocity vector will point in the same direction as its motion. In this case, the magnitude of the velocity vector (which represents the object's speed) will be equal to the object's speed.
Example:
* A car traveling at 60 mph due east has a speed of 60 mph and a velocity of 60 mph east.
However, if the object changes direction, its speed and velocity will have different magnitudes.
Example:
* A car traveling in a circle at a constant speed of 60 mph has a changing velocity. While its speed remains constant, its direction is constantly changing, so its velocity is not constant.
Therefore, speed and velocity can only have the same magnitude when an object moves in a straight line and in one direction.
