Which has more cutting power: a scissors or a tin snips?
Procedure: Using the
Extreme Scissors Worksheet students try cutting a
heavy piece of cardboard or a thin piece of sheet metal with a pair of scissors.
Then they try doing the same thing with a pair of tin snips, and decide which one
cuts more easily. To confirm their observations, they measure the mechanical
advantage of each device.
A pair of scissors and a pair of tin snips have the same basic function: to cut
things. However, a tin snips will cut through sheet metal, or a thick piece of
cardboard, while a scissors will not. How come?
The fact that a tin snips can cut through thicker materials than a scissors
suggests that it can cut with more force. The increased force is at the load end,
because the user is supplying about the same the effort force with his or her hand.
The ratio of these two is what we have been calling mechanical advantage or M.A.
(see p. 25):
MECHANICAL ADVANTAGE (M.A.) =
EFFORT ARM
LOAD ARM
=
LOAD FORCE
EFFORT FORCE
In Salad Tongs Geometry, we found that the same ratio can be gotten by
measuring the input and output ranges of motion. Combining all of these, we
have:
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