Embedded Files
A lever consists of a rigid element, similar to a bar, which rotates around a point, called a fulcrum, on which several forces act in equilibrium. Each force produces a turning moment in the lever. The moment is the product of the force times its distance from the pivot point.
Where F is the force we apply, R the resistance (we call it resistance because it is usually the force we want to overcome), and d and r their respective distances to the support point
Where:
P=Power, or force applied
R=Resistance load
Bp=Distance between fulcrum and the power force
Br=Distance from the fulcrum to the Resistance
Equilibrium in the lever occurs when the momentum of the forces trying to rotate the bar to one side is equal to the momentum of the forces trying to rotate the bar to the opposite side. Therefore, any lever in equilibrium will satisfy the law of the lever, which is mathematically expressed as follows:
This mathematical expression has a very important practical interpretation: "the greater the distance of the applied force to the point of support (force arm), the smaller the effort required to overcome a given resistance" (BF↑ F↓). (BF↑ F↓)
Exercises
Exercises
Calculate the force that would have to be applied (F) to move a weight of 200 kg by means of a bar supported on a pivot located 2 metres from the weight to be moved, and 5 metres from the point of application of the force.
Solution:
Applying directly the law of the lever and clearing the force to be applied F, we obtain:
F ·BF = R · BR
F = (R - BR) / BF = (200 - 2) / 5 = 80 Kg
In other words, to lift a weight of 200 kg, using a lever such as the one shown, you only have to exert a force of 80 kg.
Mechanical advantage = 200 Kg / 80 Kg = 2,5
Page updated
Google Sites
Report abuse