A child on a playground
swing illustrates the difference between
potential and kinetic energy.
The Law of the
Conservation of Energy
Energy can be changed in
form, but cannot be created or destroyed; this is
the basic law of the conservation of energy.
Machines Change the Directions of Motion
Changing linear motion to
rotary motion requires some kind of piston, a
connecting rod, a crankshaft, and a flywheel.
Changing rotary motion to linear motion involves
the use of a wheel, drive pin, and slotted yoke.
consists of a rod or
plank that is free at both ends, and some steady
object on which the plank can rest. The braced,
or fixed, part is called the fulcrum.
The distance from the load to the fulcrum is the load
arm. The distance between the fulcrum and
the lifting force is the effort arm.
The secret of the
inclined plane's mechanical advantage: for an
object resting on the plane, the vertical force
of gravity acting on it is split into two smaller
forces, one perpendicular to, one parallel to the
can be imagined as a
cylinder with an inclined plane wrapped around
it. A screw finds its mechanical advantage in the
ratio of two dimensions: the length of the lever
that turns it and the distance between threads (pitch).
is essentially a double
inclined plane. It differs from the inclined
plane, however, in that it is intended to be
pushed under or into the load instead of having
the load pushed or pulled up along the plane.
is a first-class lever.
The center of the axle corresponds to the
fulcrum. The radius of the axle corresponds to
the load arm. The radius of the wheel corresponds
to the force, or effort, arm to which force is
applied. Sometimes a crank is used instead of a
is a wheel over which a
rope or belt is passed for the purpose of
transmitting energy and doing work. The simplest
pulley is a grooved wheel on a fixed axle. A rope
passed over this wheel is tied to the load to be
lifted, and a pull is applied to the other end of
Gears and Ball Bearings