Consider a steelyard as in the picture. We know that the steelyard is in equilibrium.Where’s the fulcrum? Where does the normal force act? Determine the normal force and the lever arm bc.

Fc= 5NFx=20Nbx=10cm

bc= ?Fn= ?

Mechanical advantage

• The LOAD divided by the EFFORT is called the MECHANICAL ADVANTAGE

M.A.= L/EA mechanical advantage greater than one means that the load overcome is greater than the effort, you have an advantage using the machine.

Considering the inclined plane M.A.= W/W// = l/h

LEVERWe call LEVER any rigid objectnwhich is pivoted about an axis called the FULCRUM (F). The Load and the Efford can be applied on either or the same side. According to the side the forces are applied we define THREE classes of lever:

• Class 1(crowbar) L= 1000N

E= 25NbL=5cm bE= ?

We can think to move anything with a little force, it’s enough to use levers with a long arm

• In class 1 levers the pivot is between Load and Effort.

• How much is the mechanical avantage ?For Equilibrium L•bL-E•bE = 0

L/E= bE/bL

We have an advantage using a class 1 lever when bE>bL

Lever class2

• Load between Effort and Fulcrum , M.A. > 1 because bE>bL

Lever class 3

effort

loadpivot

Effort between Load and Fulcrum , M.A. < 1 because bE < bL