Biomedical Engineering Reference
In-Depth Information
Chapter 1
Forces
When muscles of the human body exert forces, they can set an object into motion or
even change its state of motion. These muscular forces can cause deformation of
bodies that is generally not visible to the unaided eye. Forces of many types control
all motion in the universe.
1.1 Objectives
To describe a force
To represent a force by a vector using a scale and specifying its magnitude and
direction
To perform operations with vector forces and to determine the resultant force
To calculate the pressure produced by a force on a surface
1.2 Concept of Force
Force is associated with a push (compression) or a pull (tension or traction) as
shown in Fig.
1.1
. Forces can produce motion, stop motion, or modify the motion of
bodies on which they act. Forces can also deform the body on which they act.
Forces are always applied by one body on another body.
A push on an object (e.g., a toy) uses a muscular effort to produce a movement
that has the direction of this push. A pull on the toy in the opposite direction will
reverse the motion. A force can be represented by a vector. The length of the vector,
represented by an arrow, gives the magnitude of the force, and its tip indicates the
direction. Force is measured in newtons (N) in the International System of Units
(SI). Remember that magnitude and direction characterize a vectorial quantity. The
forces in Fig.
1.1
are called contact forces, since these forces occur with two bodies
in contact. The forces exerted by gases on the walls of a container, or our feet on the
ground, are examples of contact forces.
