Graphics Reference
In-Depth Information
Consider a racing car being propelled by a given force. As it loses mass due to fuel
consumption, the force applied, if constant, will result in an increase in speed.
Now consider a body in space as it moves through other material. The original
object gains mass. Its collisions with other particles (however small) will slow
down the object, but additional slowing will also occur due to the additional
mass. A bus traveling down a street will slow down as more and more people
climb aboard until it gains so much mass that the force is no longer sufficient
to maintain the momentum, and it will stop.
FIG 2.8
As mass is lost on a moving
object, speed will increase if the force
is maintained. If a body gains mass
during motion, it will slow down.
Newton's Third Law of Motion
Newton's third law of motion states simply that every action has an equal and
opposite action in direction and magnitude. The direction of both actions
occurs along the same line, so when one object exerts a force on a second
object, that second body exerts a reciprocal force on the first along that line.
When a horse is hauling a heavy cart, for example, the force the horse exerts on
the load results in the load moving forward. However, the force that the horse
exerts is reciprocated by the force that the load exerts on the horse. Although
the actions and the forces are equal, the velocities of the individual objects
FIG 2.9
Every movement has an
equal and opposite action. The horse
pulling a load exerts forward move-
ment, the load exerts backward forces.
