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Q & A: Levers

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Most recent answer: 09/22/2015
Q:
what is a lever and how does it work?
- ben (age 9)
canada
A:
A lever is a rigid bar that can turn around a pivot point, called a fulcrum. A lever is a simple machine and can be moved to move a load (or do work). Effort is applied to one part of the lever and it pushes the load at another part. Using a lever makes it easier to move a load and so you use less effort.

There are three kinds of levers:

1) First Class Lever -- the effort and the load on either side of the fulcrum. Some examples would be a crowbar or a seesaw. The effort is only less than the load if the load is closer to the fulcrum. The lever then acts as a force magnifier and the mechanical advantage is greater than one. If the effort is closer to the fulcrum, then the effort is larger than the load and the mechanical advantage is less than one. In this case the lever acts as a movement magnifier.

2) Second Class Lever -- the load is between the fulcrum and the effort. An example is a nutcracker or a wheelbarrow. This type of lever always acts as a force magnifier and its mechanical advantage is greater than one.

3) Third Class Lever -- the effort is between the load and the fulcrum. An example is a pair of sugar tongs. This is a movement magnifier which means its mechanical advantage is less than one. The load moves more than the effort. (When you use sugar tongs, a small movement of the fingertips makes the jaws of the tongs move a lot.)

(published on 10/22/2007)

Follow-Up #1: A fulcrum is...

Q:
what is fulcreum
- Anonymous
A:
A fulcrum is the support, or pivot point, about which a lever turns.  Consider a see-saw, two kids on either side of a board.   The fulcrum is the thing in the middle that holds it up. 

LeeH

(published on 10/22/2007)

Follow-Up #2: How does a lever give an advantage?

Q:
How does a lever give an advantage?
- allison (age 13)
USA
A:

That is because force is not a conserved quantity, but the energy is. The energy expenditure (=work) is the product of the force and the distance along which you apply this force. Therefore, the you can do the same work by increasing the length and decreasing the applied force, which is how the levers give you an advantage. By this way, you can apply forces larger than you can, but with the compensation that you need to pull a lever or a rope longer with same proportionality.

Tunc


(published on 09/22/2015)

Follow-up on this answer.