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:
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:
Load (L): A resistive force that is to be overcome by a machine is called the Load.
S.I. unit is Newton (N).
Effort (E): An external force applied to a simple machine to overcome a load is called the Effort. S.I. unit is Newton (N).
Fulcrum (Pivot, F): The point on which something turns or is supported.
Mechanical advantage (MA): The ratio of Load (L) to overcome the magnitude of
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)
the Fulcrum (pivot)
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.
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.
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.
This is a first-class lever, it has Fulcrum (pivot) in the middle, Load at one end, and effort on the other.
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.
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.
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
In the above image, La > Ea.
So, MA < 1, therefore works as a
Here, La > Ea
MA = Ea / La
As, Ea < La, implies that MA < 1
Change in direction
= Distance travelled by effort (m) / Distance travelled by Load (m)
= Effort (E) * distance traveled by an Effort (n)
= Work output / work Input
= Mechanical advantage / Velocity ratio
= M.A. / V.R.
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