physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

, and in particular in

biomechanics Biomechanics is the study of the structure, function and motion of the mechanical aspects of biological systems, at any level from whole organisms to Organ (anatomy), organs, Cell (biology), cells and cell organelles, using the methods of mechani ...

, the ground reaction force (GRF) is the

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

exerted by the ground on a body in contact with it. For example, a person standing motionless on the ground exerts a

contact force A contact force is any force that occurs because of two objects making contact with each other. Contact forces are very common and are responsible for most visible interactions between macroscopic The macroscopic scale is the length scale on ...

on it (equal to the person's

weight In science and engineering, the weight of an object is a quantity associated with the gravitational force exerted on the object by other objects in its environment, although there is some variation and debate as to the exact definition. Some sta ...

) and at the same time an equal and opposite ground reaction force is exerted by the ground on the person. In the above example, the ground reaction force coincides with the notion of a

normal force In mechanics, the normal force F_n is the component of a contact force that is perpendicular to the surface that an object contacts. In this instance '' normal'' is used in the geometric sense and means perpendicular, as opposed to the meanin ...

. However, in a more general case, the GRF will also have a component parallel to the ground, for example when the person is walking – a motion that requires the exchange of horizontal (

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of t ...

al) forces with the ground. The use of the word

reaction Reaction may refer to a process or to a response to an action, event, or exposure. Physics and chemistry *Chemical reaction *Nuclear reaction *Reaction (physics), as defined by Newton's third law * Chain reaction (disambiguation) Biology and ...

derives from Newton's third law, which essentially states that if a force, called ''action'', acts upon a body, then an equal and opposite force, called ''reaction'', must act upon another body. The force exerted by the ground is conventionally referred to as the reaction, although, since the distinction between action and reaction is completely arbitrary, the expression ''ground action'' would be, in principle, equally acceptable. The component of the GRF parallel to the surface is the frictional force. When slippage occurs the ratio of the magnitude of the frictional force to the normal force yields the coefficient of static friction. GRF is often observed to evaluate force production in various groups within the community. One of these groups studied often are athletes to help evaluate a subject's ability to exert force and power. This can help create baseline parameters when creating strength and conditioning regimens from a rehabilitation and coaching standpoint. Plyometric jumps such as a drop-jump is an activity often used to build greater power and force which can lead to overall better ability on the playing field. When landing from a safe height in a bilateral comparisons on GRF in relation to landing with the dominant foot first followed by the non-dominant limb, literature has shown there were no significances in bilateral components with landing with the dominant foot first faster than the non-dominant foot on the GRF of the drop-jump or landing on vertical GRF output.Ball, NB, Stock, CG, Scurr, JC. Bilateral Contact Ground Reaction Forces and Contact Times During Plyometric Drop Jump. Journal of Strength and Conditioning Research; October 2010 – Volume 24 – Issue 10- pp 2762-2769

References

{{Authority control Mechanics Biomechanics