Biomechanics of Sport and Exercise Chapter One: Forces

vector

Mathematical representation of any quantity that is defined by its size or magnitude (a number) and its direction (its orientation); vector quantities may be represented graphically by arrows, with the length of the arrow scaled to represent the magnitude of the vector and the shaft and head of the arrow oriented to represent the direction and sense of the vector along the direction.

limiting friction

Peak static friction that can be produced between two surfaces for a given normal contact force; the maximum friction just before the two surfaces start to slide

tensile forces

Pulling forces whose direction and point of application would tend to lengthen or stretch an object along the dimension coinciding with the line of action of the force.

compressive forces

Pushing force whose direction and point of application would tend to shorten or squeeze an object along the dimension coinciding with the line of action of the force.

gravitational acceleration

The rate of change in velocity caused by the force of gravity; approximately 9.81 m/s2 downward or 32ft/s2 downward; also referred to as acceleration due to gravity; often abbreviated as g.

static equilibrium

The state or condition of an object that results when the object is not moving and the next force and net torque acting on the object are zero.

net force

The vector sum of all the external forces that act on an object; the resultant of all the external forces that act on an object; the resultant force.

resultant force

The vector sum of two or more forces; the force that results from the vector addition of two or more forces.

colinear forces

Two or more forces that have the same line of action (but not necessarily the same direction along this common line of action).

concurrent forces

Two or more forces whose lines of action intersect at a single point.

static friction

Frictional force that develops between two surfaces in contact that are not moving relative to each other.

external force

A force that acts on an object as a result of its interaction with the environment surrounding it.

internal force

A force that acts within the object or system whose motion is being investigated; forces between the molecules of an object that hold the object together.

contact forces

A force that results when two objects touch each other.

force

A push or pull expressed as units of mass times units of length divided by units of time squared or as newton in SI; a vector quantity.

free-body diagram

A tool for analyzing forces and torques; a drawing of the object of analysis with all external forces acting on the object represented as arrows showing their points of application and directions.

dynamic friction

Frictional force that develops between two surfaces in contact that are moving or sliding relative to each other; sliding friction; kinetic friction.

acceleration due to gravity

Gravitational acceleration: The rate of change in velocity caused by the force of gravity; approximately 9.81 m/s2 downward or 32ft/s2 downward; also referred to as acceleration due to gravity; often abbreviated as g.

tension

State of an object as a result of forces pulling on it and producing tensile stress; tensile stress is axial stress that tends to pull molecules apart and stretch the object.

friction

The component of a contact force that acts parallel to the surfaces in contact; the magnitude of friction is the product of the coefficient of friction and the normal contact force (the component of the contact force acting perpendicular to the surfaces in contact).