Some machines are designed to be "force
multipliers" - their mechanical advantage
is greater than 1. Other machines are
designed to be speed and displacement
multipliers. Their mechanical advantage
is less than 1. Force multipliers,
mechanical advantage greater than 1,
meaning 2, 3, 5.7, whatever it happens to
be. These things are designed to take a
smaller input force and give you a
larger output force. The idea is that the
output force should be greater than the
input force - that's the goal. But as a
result, unfortunately, because of the
nature of our universe and the law of
conservation of energy, that input force,
which is relatively small, must be
applied at a higher speed or over a
larger displacement to get that larger
output force over a smaller output
displacement, or at a smaller velocity.
Some examples - your steering wheel - as you
apply force to your steering wheel it
turns a small shaft which then turns the
box at the end of the wheel. The electric
drill - the electric motor moves quite
quickly and the drill output moves quite
slowly. Screwdriver, pliers, scissors,
doorknobs, all those things are designed
to increase the force that you apply to
give a larger output force than input
force. There is, however, this whole other
class of machines which is a "speed
displacement multiplier" and the
mechanical advantage is less than 1.
Not negative numbers but fractions and
decimals between 0 and 1. So 0.1, 1/2,
0.75. All those are speed and
displacement multipliers. They are
necessarily "forced dividers" as a result
of being speed displacement multipliers
because of the nature of our universe.
some examples - The idea is that the goal
is to get a large output displacement or
a large output speed from a
small input displacement or input speed.
But unfortunately you have to apply
a large input force to get a small
output force, so clearly that's not the
goal. But you do get a small output force
over a large displacement or a larger
speed. So the goal of these machines, and
sometimes it seems to be a bit
counterintuitive like this
excavator, those big machines that lift
large amounts of dirt in the big bucket
and then move it with their big arm to
some other place. Those excavators are
actually machines with the mechanical
advantage less than 1.
Lacrosse stick, the goal is to get that
thing to move fast. Catapult, you want to make
the rock or whatever you put in the
catapult move quickly. Bicycle moves
quickly. A broom is designed to move
farther. Your arms and legs - your muscles
are capable of contractions, strong
contractions, over short displacements so
your arms and legs are designed to take
that small displacement, large force and
put out a larger displacement, smaller
force. And depending on the machine
sometimes you want it to be a speed
displacement multiplier. Sometimes you
want that machine to be a force
multiplier. But always remember a force
multiplier can be identified because it
is always a speed and displacement
divider. So you can just watch that
machine and if the output speed or
displacement is greater than the input
speed or displacement, it has to be a force
multiplier but if it makes it go faster
it's got to be a speed displacement
multiplier and as a result, unfortunately,
has to be a force divider.