Types of Lever

Introduction

In our daily life, we see many objects around us such as a see-saw in the park, spoons in the kitchen, scissors, bottle openers, joints in the human body.


What is common in these objects?


Well! These all have a lever. 


Now you might be wondering what is a lever?


The lever is a rigid bar which basically allows a heavier or a steadfast object lying on the fixed point  with a smaller force


Three different types of levers exist, depending on where the input force, fulcrum, and load are. 

  •  A first-class lever has the fulcrum (fixed point) between the input force and load.

  •   A second-class lever has the load between the fulcrum (pivot) and the input force.

  •  A third-class lever is a lever that has the input force in the middle of the fixed point and the load.

On this page, we shall learn the following things: 

  • What are simple machines?

  • Fulcrum, Lever, Effort, Load

  • First-class, second-class and third-class lever

  • Mechanical advantage (MA)

  • Examples (Real-life)

What are Simple Machines?

The word machine has come from the Greek word which means "to help make things easier."Energy still remains conserved because machines can't do work more than the energy we put in.


It helps to reduce the input force  (Effort) to perform a job.


Now, let's talk about the Lever.


The lever is nothing, but a rod and 

the things we encounter in day-to-day

life having a rod-like function is "Lever."


Lever has a fixed point through which it is easy to rotate it about that point.


Such as a bottle opener, scissors, pliers, stapler, nut-Cracker; etc. 


Let’s talk about basic definitions:

  1. Load (L): A resistive force that is to be overcome by a machine is called the Load.

                  S.I. unit is Newton (N).

  1. Effort (E): An external force applied to a simple machine to overcome a load is called the Effort. S.I. unit is Newton (N).       

  1. Fulcrum (Pivot, F): The point on which something turns or is supported.

  1. Mechanical advantage (MA): The ratio of Load (L) to overcome the magnitude of 

                Effort (E).               


Where MA is nothing but the ratio of Effort arm to the Load arm, which we would be discussing in the class of Levers.


   MA  = Effort Arm (E)  /  Load Arm (L) 

     Effort Arm (E) = The distance between the effort (force) and 

          the Fulcrum (pivot)

        Load Arm (L) =  The distance between the Load and the

          Fulcrum     (pivot)

Types of Levers    

First-Class lever


Here, it is a first-class lever.


In this, we can see that we have to apply

an effort (force) against gravity. 


Like, in a garage, a screw jack is fixed at the bottom and as we start rotating the jack, the car moves upwards, here we applied little force, and the car applied that force to move upward.


Second-class lever


Did you notice that when you try to tear the paper into equal parts manually, it takes much time?

If you use scissors, then the time would be saved, though the effort applied was less, the work got done in speed.

Which means the speed is increased here to get the job done earlier.


Third-class lever

You might've been to villages, where people 

depend upon the well as a water resource, they apply their effort upward in pulling out the water from the well via the bucket attached to the string, but it is easy to use a pulley, then the effort would've been downwards (towards the gravity). Hence the effort applied would be less.

Classification of Levers on the basis of MA

S.no

Type of lever

Mechanical advantage

Attribute

1.

First-class lever

Greater than 1

Force multiplier

2.

Second-class lever

Less than 1

Speed multiplier

3.

Third-class lever

Equal to 1

Change in direction of the effort

It can work as a force multiplier, speed multiplier and in changing  the direction of Effortas well (Depending on the value of MA)


Let’s Understand:

This is a first-class lever, it has Fulcrum (pivot) in the middle, Load at one end, and effort on the other.

  • Examples of the First-class lever

  1. See - Saw


Here,  in this case:

   

 The Fulcrum (pivot) is between the Load and the Effort such that

Length of Load Arm (La) = Length of Effort Arm (Ea).]

           

              MA (Mechanical advantage) = Ea / La

                 As  Ea = La

                 

                      MA = 1


 Which means the change in direction.


2. Pliers

                          

Here, Ea >  La, as you can see in the image above that the Effort Arm is greater than the Load Arm.


 As we know, MA = Ea/ La,

 

 Here, Ea > La, MA > 1


Therefore, it works as a Force Multiplier.


3. Scissors   

           

In the above image of scissors, we can see that the Length Arm > Effort Arm:


             As, MA = Ea / La


              And, Ea < La


             So, MA  < 1


Here, it works as a Speed Multiplier

  • Example of a second-class lever


In the above image, La > Ea.

So, MA < 1, therefore works as a

Speed Multiplier.     

  •    Example of a  third-class lever


Here, La >  Ea


                   MA = Ea / La

                   As, Ea < La, implies that MA < 1


            Change in direction

 Velocity ratio:                   

                      = Distance travelled by effort (m) / Distance travelled by Load (m)                     

  Work Input:

        = Effort (E) * distance traveled by an Effort (n)

 Efficiency (p): 

 = Work output / work Input

=  Mechanical advantage / Velocity ratio 

 =  M.A. / V.R.

Summary:

 

We call levers as simple machines because they have only two parts - Fulcrum and the Handle, where the handle or bar of the lever is called the “Arm,” and Fulcrum is the point on which the lever rotates.


Short Question answers:


Q1: The efficiency of a machine is 60 %. If 500 Joule of energy is given to the machine. What is its output?


Sol: Efficiency (p) = 60%, Input (i) = 500 J

Output = p * i

   = 60/100 * 500

   Therefore, Output  = 300 J


Q2: Explain why scissors for cutting cloth may have blades longer than the handles but shears for cutting metals have short blades and long handles?


Ans:  A pair of scissors used to cut a piece of cloth has blades longer than the handles so that the blades move longer on the cloth than the movement at the handles. While shears used for cutting metals have short blades and long handles because it enables us to overcome 

large resistive force by a small effort.


Q3: A pair of scissors has its blades 10 cm long, while its handles are 2.5 cm long. What is its mechanical advantage? 

 

Ans: Effort Arm ( Ea) = 2.5 cm

        Length Arm = 20 cm

M.A. = Ea/ La 

        = 2.5/ 10

  Therefore, M.A.    =   0.25