In the realm of physics, magnitude refers to size or quantity alone. When it comes to movement, magnitude refers to the speed at which an object is traveling or its size.
In physics — the study of motion distance, velocity, speed and mass expressed as quantities — is divided between vectors and scalars. A one-dimensional scalar is described by its magnitude alone, while a two-dimensional vector is fully described by its magnitude and direction.
Speed is the magnitude of the movement. To describe velocity, both magnitude and direction are required. In depicting a vector in a vector diagram, or free-body diagram, the magnitude is represented by the length of the arrow.
Order of magnitude calculations are essentially an estimate. They are used in physics to approximate calculations and determine the appropriateness of values without the use of complex calculations or when precise values are unavailable. They can also be used to check the reasonableness of more precise calculations. Order of magnitude calculations are useful when comparing items that are 100 times each other or more. The amount in question is estimated to the power of ten; for example, the population of a municipality may be estimated in the tens of thousands, hundreds of thousands or millions.