- Dynamics is the study of how bodies interact with
one another; it answers the question, "Why does
the motion of a ball change?"
- Isaac Newton expressed a set of three rules which
allow one to predict the result of interactions
between objects. These are known as Newton's Three Laws
of Motion.
- The quantities which these rules govern are
- acceleration (m/s^2)
- mass (kg)
- force (kg-m/s^2)
- Inertia is a property of objects: the degree to which
they resist changes in their motion. It turns out that
the inertia of an object is directly proportional to its mass:
the more massive it is, the harder one has to push to move it.
- Weight is the force exerted downwards by a body in
a gravitational field. It is not the same as mass.
- Newton's First Law:
A body at rest stays at rest, and a body in motion continues
in motion with constant velocity, unless some external force
acts upon it.
- Newton's Second Law
The acceleration of an object is directly proportional to the
force applied to it, and inversely proportional to its mass.
In other words,
F = ma
- Newton's Third Law
If a body exerts a force on a second body, then the second
body exerts an equal and opposite force on the first.
But note that the result of these opposing forces depends on
the mass of each body.