Why is the Time Period of a Pendulum & SHM Different?

[Anoushka]

can someone please tell me why is the time period of a simple pendulum independent of the mass m of the bob while the time period of a simple harmonic oscillator is T=2∏√m/k!
pleaseeeee help .

Thankyou sooo much :)

 

[collinsmark]

Hello Anoushka,

Welcome to Physics Forums!

can someone please tell me why is the time period of a simple pendulum independent of the mass m of the bob while the time period of a simple harmonic oscillator is T=2∏√m/k!
pleaseeeee help .

Thankyou sooo much :)

I can't give you the answer, but I will give you a couple things to consider.

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// Consideration 1
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It has been said that Galileo Galilei performed an experiment in which he simultaneously dropped two dense objects with unequal masses from the Leaning Tower of Pisa. Contrary to to the popular predictions of many other people, the objects hit the ground at the same time (even though one was significantly heavier than the other).

Jump forward a century or so and consider Isaac Newton's second law of motion.

[tex] \vec F = m \vec a [/tex]
Even if the mass [itex] m [/itex] is a variable in this equation, what it is that remains constant when considering objects falling due to gravity? Does [itex] \vec F [/itex] remain constant or does [itex] \vec a [/itex]?

Now it might help to repeat the same consideration, except instead of objects in perfect free fall, apply the considerations to various sized masses on a frictionless incline.

Can you see the relationship between that and an approximation to a pendulum? (Hint: assume small angles)

//=============
// Consideration 2
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Now consider various sized masses attached to a particular, ideal spring. Suppose the spring also has particular compression x₀ at some point in time.

Don't forget Newton's second law,
[tex] \vec F = m \vec a [/tex]
In this situation with a particular spring at a particular displacement, what is it that stays constant even if the mass changes? Does [itex] \vec F [/itex] remain constant or does [itex] \vec a [/itex]?

 

[marty1]

A pendulum is an example of a simple harmonic ocillator.

Think about this too:

When you increase the mass of the pendulum the intertia of the pendulum increases the same as the force of gravity on the pendulum. The extra force of gravity is canceled exactly by the increase in inertia. Hence the resulting acceleration is constant but for a larger mass it take more force to achieve. Exactly the extra force provided by the addition mass.

 

[Anoushka]

A pendulum is an example of a simple harmonic ocillator.

Think about this too:

When you increase the mass of the pendulum the intertia of the pendulum increases the same as the force of gravity on the pendulum. The extra force of gravity is canceled exactly by the increase in inertia. Hence the resulting acceleration is constant but for a larger mass it take more force to achieve. Exactly the extra force provided by the addition mass.

Marty1 and Collinsmark thanks a lot you guys , that was really helpful! :D

 

[Nickie]

The time period of a pendulum and simple harmonic oscillator (SHM) may seem similar, but they are actually different due to the underlying principles that govern them. The time period of a pendulum is determined by the length of the pendulum and the acceleration due to gravity, while the time period of a SHM is determined by the mass and the spring constant.

In a pendulum, the mass of the bob does not affect the time period because the force of gravity, which is responsible for the motion of the pendulum, is independent of the mass. This means that no matter the mass of the bob, the pendulum will take the same amount of time to complete one swing.

On the other hand, in a SHM, the time period is directly proportional to the mass and inversely proportional to the spring constant. This is because the force that drives the SHM is dependent on the mass and the strength of the spring. A larger mass or a weaker spring will result in a longer time period for the oscillator.

So, while both a pendulum and a SHM exhibit periodic motion, their time periods are determined by different factors. It is important to understand the underlying principles and equations that govern these systems in order to fully grasp the differences in their time periods. I hope this helps clarify the concept for you.