Types of Motion & Simple Machines in Biomechanics and Therapy

linear motion (translatory motion)

It occurs when all parts of an object move the same distance, in the same direction, and at the same time (e.g., child sledding down a hill).

curvilinear motion

Movement occurring in a curved path that is not circular (e.g., skier coming down a slope).

angular (rotary) motion

Movement around a fixed point (axis), where all parts of the object move through the same angle, in the same direction, and at the same time, but not the same distance (e.g., knee flexion/extension).

simple machines

Tools that change the magnitude or direction of force required to lift or move a load. Examples include levers, pulleys, and inclined planes.

mechanical advantage

The relationship between force expended and load moved, measuring the effectiveness of a machine.

distance effect on force in simple machines

Increasing the distance over which force is applied reduces the force needed; decreasing the distance increases the required force.

linear motion in physical therapy

Pushing a wheelchair or a patient walking in a straight path demonstrates

curvilinear motion in clinical application

Movements such as throwing a ball or guiding a patient through an arcing arm exercise follow a curvilinear path.

angular motion in rehabilitation

Joint range of motion exercises (e.g., elbow flexion/extension) are angular motions around the joint axis.

mechanical advantage with levers

By adjusting hand placement during manual resistance exercises, therapists can increase or decrease the mechanical advantage to safely grade the patient's effort.

importance of force and distance relationships in therapy

It helps therapists modify exercises to reduce patient strain, improve efficiency, and prevent injury (e.g., moving resistance further from a joint increases effort required).