What is a Second Class Lever?
In
second class levers, the load is between the force and fulcrum on the lever
arm, as shown in the figure. In this kind of lever, the force is always further
from the fulcrum than the load. As a result, the load does not move as far as
the applied force, but the force of the load will always be greater than the
applied force. The closer the load is to the fulcrum, the more the force of the
load increases and the easier it becomes to raise the load. The direction of
the force and the load always oppose one another in a second class lever. A
second class lever always magnifies force and decreases the distance moved.
Example of a Second Class Lever
A
wheelbarrow is an example of a second class lever. The axle of the wheel is the
fulcrum, the load is that which is being carried and the force is applied to
the handles.
Second
class levers are similar to first class levers. Second class levers always
multiply the input force, however they do not change its direction. Second class
levers always have the output force between the fulcrum and the input force,
this ensures that it has a mechanical advantage. Wheel barrows, staplers and
bottle openers are all good examples of second class levers.
Mechanical advantage
- v A second-class lever allows a large load to be lifted by a smaller effort. Another way to say this is that the mechanical advantage of a lever is the ratio of lengths between the input arm and the output arm. If the input arm is 5 meters and the output arm is 1 meter, then the mechanical advantage will be 5. The output force will be five times as large as the input force
Characteristics
v Because the load is always closer to the fulcrum, the effort is always less than the load.
v Because the load is always closer to the fulcrum, the effort is always less than the load.
Activity
- 1. Use the pencil, ruler, and washer to make the first lever shown. Use the lever to lift the load.
- 2. Then build the next two levers and see how much force it takes you to lift the load using them.
- 3. Label the lever arms on each lever.
- 4. Circle the lever that took the least amount of force to lift the washer.
