Explain why scissors for cutting cloth may have blades longer than handles, but shears for cutting metals have short blades and long handles. – to explain this we need a comparison of Scissors & shears with their mechanical advantage.
Scissors and shears apparently may look identical. Both of them belong to the class I lever, having the fulcrum in between load and effort.
As Scissors with longer blades are used to cut cloth, less movement of the handle can cut more length of the cloth. This helps to gain speed and can cut cloth faster as a speed multiplier. Shears with longer handles provide a mechanical advantage value greater than 1 and acts as an effort multiplier. This means using shear heavier load like metal can be cut using less amount of effort.
We will discuss this in more detail below.
Comparison of Scissors & shears with their mechanical advantage
Scissors for cutting cloth with blades longer than the handles make their mechanical advantage value less than one (because here load arm > effort arm).
But as scissors have longer blades the displacement at the load end is more than the displacement at the effort end. As a result, less movement of the handle can cut more length of the cloth. So this gives a speed gain.
That’s why scissors with long blades are considered a speed multiplier and this helps to cut cloth faster.
Shears, on the other hand, have short blades and longer handles.
That means in this case, effort arm > load arm and we get a mechanical advantage value greater than 1.
Shears to cut metal require to have a smaller effort get multiplied to overcome the heavier load. The mechanical advantage of shears is more than 1 and that helps shears to fulfill that objective.
Here shears with short blades and longer handles act as an effort multiplier.
Note that, Mechanical advantage of levers = Effort arm / Load arm.
Study more about MA and its formulas here: MA of levers ]
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