Simple Machines: These
devices were all in common use for centuries before Leonardo's time. Each one
makes work easier to do by providing some trade-off between the force applied
and the distance over which the force is applied.
Wheel and Axle In this machine a
wheel or spoke is locked to a central axle so that when one is turned the
other must turn. A longer motion at the edge of the wheel is converted to a
shorter more powerful motion at the axle. In reverse, a short powerful force
at the axle will move the wheel's edge a greater distance.
Pulley System A single
pulley simply reverses the direction of a force. When two or more pulleys are
connected together, they permit a heavy load to be lifted with less force. The
trade-off is that the end of the rope must move a greater distance than the
load.
Wedge A wedge converts
motion in one direction into a splitting motion that acts at right angles to
the blade. Nearly all cutting machines use the wedge. A lifting machine may
use a wedge to get under a load. Screw A screw is a central core
with a thread or groove wrapped around it to form a helix. While turning, a
screw converts a rotary motion into a forward or backward motion.
Lever A lever is a stiff rod that
rotates around a pivot point. Downward motion at one end results in upward
motion at the other end. Depending on where the pivot point is located, a
lever can multiply either the force applied or the distance over which the
force is applied.
Other Elements of
Machines: Though these devices were also used in machines in
Leonardo's time, he experimented with them and made changes to improve how they
worked. He also combined them in many exciting new ways to create machines and
inventions that had never been seen before.
Gears Gears are toothed or pegged
wheels meshed together to transmit motion and force. In any pair of gears the
larger one will rotate more slowly than the smaller one, but will rotate with
greater force. Each gear in a series reverses the direction of rotation of the
previous gear.
Bevel Gears Gears that
mesh at an angle change the direction of rotation.
Worm Gear A worm gear is a
combination of a gear meshed with the threads of a screw. This combination
changes the direction of turning motion by ninety degrees. Worm gears also
decrease the speed of turning from screw to gear and increase its force.
Rack and Pinion A single
gear, the pinion, meshes with a sliding toothed rack. This combination
converts rotary motion to back and forth motion. Windshield wipers in cars are
powered by a rack and pinion mechanism. A small pinion at the base of the
wiper meshes with a sliding rack below. Cam A cam is a wheel with shaped
bumps on it. Cams are often connected to rods, levers, or springs. In the
gravity trip hammer shown here, the bumps on the turning cam push down on the
end of the lever making it raise the hammer again and again. Crank and Rod The crank is a
wheel with a pivoting arm attached near its edge. The arm is attached by a
hinge to a rod. When the crank turns, the rod is pushed back and forth.
Alternatively, if the rod is pushed back and forth at the right speed, the
crank will turn. The crank and rod shown here are part of giant steam
engine. Chains and Belts A chain or belt
connects two separated wheels so that one turns, the other will turn in the
same direction.
Ratchet A ratchet
is a device that allows a wheel to turn in only one direction. The ratchet
wheel has specially shaped teeth. A bar on a pivot called the "pawl" is fixed
above the ratchet wheel. The pawl slides over the teeth of the ratchet in one
direction, but blocks the motion of the teeth if the wheel turns in the other
direction.
Now that you have seen the various elements of
machines, you can try to figure out which ones are used in some common
devices by going to the Gadget
Anatomy page.
Lever
