SCIE 4001
3.5 Simple Machines
3.5 Levers
3.5 Wheel & Axle
3.5 Inclined Plane
3.5 Pulley
3.5 Screw
3.5 Wedge
 

Unit 3 STRUCTURE AND MECHANISMS

3.5 Levers

"Give me a lever long enough and a fulcrum on which to place it, and I shall move the world." Archimedes

A lever is one of the simplest mechanical devices. A lever can be made from a beam or stick or rod with a sharp edge on which to pivot. This pivot is called a fulcrum. A lever is often used to magnify the effort exerted to lift weights with less effor, but levers can sometimes be used where the load is smaller than the effort. When you use a crowbar, for example, to open box or a nail to open a paint can or a board to move a crate you demonstrate the principle of levers.

lever
— Seesaws, wheelbarrows, and crowbars are levers
— Many simple devics like pliers, sissors., nail clippers, etc. are made up of multiple levers.
Typical Lever
levers

First-class levers h

— If the two arms of the lever are of equal length, as with the equal arm balance, the effort must be equal to the load.
— If the effort arm is longer than the load arm, as in the traaditional crowbar, the effort travels farther than the load and is less than the load making it a force multiplier.
— If the load arm is longer than the effort arm, as happens with the heavier person on the see-saw, the load travels farther than the effort and is less than the load making it a distance multiplier.

Fulcrum in the Centre
lever

Second-class levers have the load between the effort and the fulcrum.

— The effort always travels a greater distance and is less than the load making all second class levers are force multipliers.
— A wheelbarrow is a second-class lever. The wheel’s axle is the fulcrum, the effort is applied at the handles, and the load is placed between them in the tray.

Load in the Centre
Foerce Multiplier
 
lever

Third-class levers have the effort placed between the load and the fulcrum.

— The effort always travels a shorter distance and must be greater than the load making it a distance multiplier. The human forearm is a good example of a third-class lever — the fulcrum is the elbow, the effort is applied by the biceps muscle, and the load is in the hand. other examles are forcepts and tweezers.

Effort in the Centre
Distance Multiplier
 
   
nail clipper

 

The nail clipper actually has 3 levers.

— handle is a first class lever.
— top frame is a third class lever.
— bottom frame is a third class lever.

 

   
arm
— the biceps muscle contrasts to provide the effort and the hand isthe load which moves upward. The elbow joint is is the pivot.
   

 

Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.