Base unit (measurement) aspects of the world, such as time, distance, velocity, mass, temperature, energy, and weight, and "units" are used to describe their magnitude or quantity. Many of these quantities are related to each other by various physical laws, and as a result the units of a quantities can be generally be expressed as a product of powers of other units; for example, momentum is mass multiplied by velocity, while velocity is measured in distance divided by time. These relationships are discussed in dimensional analysis. Those that can be expressed in this fashion in terms of the base units are called .
Biomechanics of sprint running ground forces is also very important. Weyand et al. (2000) came up with the following equation for determining sprint velocity: where formula_2 is the sprint velocity (m/s), formula_3the step frequency (1/s), formula_4 the average force applied to the ground (N), formula_5 the body weight (N), and formula_6 the contact length (m). In short, sprint velocity is reliant on three main factors: step frequency (how many steps you can take per second), average vertical force applied to the ground, and contact length (distance your center of mass translates over the course of one contact period). The formula was tested by having