Basic Biomechanics: Forces, Levers, and Newton's Laws

muskuloskeletal

The major system producing human movement.

Biomechanics

Principles and methods of mechanics and apply them to the structure and function of the human body creating movement and stability.

Mechanics

Branch of physics associated with forces and the effect.

Scalar

Quantity describes magnitude only; does not have a direction, e.g., speed, length, area, volume, mass.

Mass

Amount of matter in an object.

Vector

Magnitude and direction, e.g., force, velocity, and acceleration.

Force

Amount and Direction of push or pull action; creates compression and traction.

Internal or External forces

Forces that can either act within an object or from outside it.

Concurrent

Two or more forces pushing or pulling in different directions.

Resultant force

Sum of magnitude and direction of each individual force vector

Torque

Ability of force to produce rotation about an axis

Amount of torque

Amount of force exerted and the distance it is from the axis

Moment arm

Perpendicular distance between the muscle line of pull and the center of the joint

Force arm

Linear distance from the application of force to the axis of rotation

Angle of application

Angle at which force is applied

Rotary

Perpendicular to an object

Torque is greatest

When the angle of pull is at 90 degrees and decreases if the angle decreases or increases

Angular Force

When the perpendicular distance between the joint axis and line of pull is larger

Stabilizing force

When the perpendicular distance between the joint axis and line of pull is very small

Newton's First Law

An object at rest tends to stay at rest and an object in motion tends to stay in motion

Newton's Second Law

The amount of acceleration depends on the strength of the force applied to an object

Acceleration

Any change in velocity of an object

Newton's Third Law

For every action, there is an equal and opposite reaction

State of equilibrium

Sum of all forces acting on an object = 0

Static equilibrium

Remain fixed or steady in one position

Dynamic equilibrium

Remain steady while changing positions

Simple Machines

Allow a person to exert a force greater than could be exerted by using muscle power alone

Lever System

Force arm (FA): Distance between the force and the axis

Class I Lever

The axis is located between the force and resistance

Class II Lever

Resistance between the force point and fulcrum

Class III Lever

Force is between resistance point & axis

Pulley

Consists of a grooved wheel that turns on an axle with a rope or cable riding in the groove

Fixed pulley

Simple pulley attached to a beam, used only to change direction

Movable pulley

One end of the rope attached to a beam, providing a mechanical advantage of 2.

Inclined plane

Flat surface that slants, exchanges increased distance for less effort.