Final answer:
Speed is a scalar quantity with no direction, while velocity is a vector with both magnitude and direction. They seem similar with constant speed in a straight line but differ in scenarios involving direction changes.
Step-by-step explanation:
Speed and velocity are two distinct concepts in physics. Speed is a scalar quantity, meaning it only has magnitude and no direction. Instantaneous speed is the speed of an object at a particular instant in time and can be described as the magnitude of instantaneous velocity.
On the other hand, velocity is a vector quantity, which means it has both magnitude and direction. Therefore, instantaneous velocity is the velocity of an object at a specific instant in time, expressed as a vector. This implies it accounts for the direction of the object's motion as well as its speed.
While speed and velocity can appear to be the same when an object is moving in a constant direction at constant speed, they are different because velocity includes direction. For example, if a car travels around a curve, its speed might remain constant but its velocity changes due to a change in direction.