BSL Physics Glossary - instantaneous speed - definition. Definition: When the speed of an object is constantly changing, the instantaneous speed is the speed of an object at a particular moment (instant) in time. Definition of instantaneous speed from the Collins English Dictionary New collocations added to dictionary Collocations are words that are often used together and are brilliant at providing natural sounding language for your speech and writing.

In terms of a displacement-time (x vs. t) graph, the instantaneous velocity (or, simply, velocity) can be thought of as the slope of the tangent line to the curve at any point, and the average velocity as the slope of the secant line between two points with t coordinates equal to the boundaries of the time period for the average velocity.