
SIMPLE MACHINES
Simple machines can be divided into 2 main categories, the
lever types and the ramp types. A lever comes in 3
classes, determined by the arrangement of the Effort, Fulcrum and
Resistance. A 1st Class lever has the Fulcrum in the middle, 2nd
class has the Resistance in the middle and 3rd class has the Effort
in the middle.The amount of work ( F x d ) that you put into a simple
machine is always less than you get out (due to frictional losses).
The advantage of a simple machine is that it can amplify forces
or distances but not both. To amplify force, distance is sacrificed and to
amplify distance, force is sacrificed.
Inclined planes (ramps) reduce effort by increasing the effort distance.
Neglecting friction, the 6 types of simple machines follow
this equation:
Win = Wout
Fe x de = Fr x dr
Now, including friction we can evaluate the
efficiency (Eff) and mechanical advantage (MA) of
a simple machine. Efficiency is just a ratio of the work the machine
puts out to the work you put in. Ideally, the maximum efficiency
would be 1 (100%), but is usually less because of frictional
losses. In other words decreasing machine friction increases efficiency.
Eff = Wout / Win
or
Eff
= Fr x dr / Fe x de
Mechanical advantage is a ratio which defines the factor by
which the force has been amplified. Any factor less than 1 amplifies
the output distance dr, greater than 1 amplifies the output
force Fr.
IMA = de/dr
Ideal Mechanical Advantage assumes 100% efficiency (no loss to friction)
The IMA of a pulley equals the number of supporting rope segments
AMA = Fr/Fe
Actual Mechanical Advantage
takes into account frictionl losses.
30 N applied to a crowbar raises a 300 N rock has an AMA of 10
Click Here for
SeeSaw Lever DEMO!
Put several masses on a seesaw in an effort to balance the
system.
Click Here
for Inclined Plane DEMO!
This lets you alter the initial velocity, mass, and angle of
a frictionless inclined plane.

