# Pendulum Amplitude Doubt

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#1
In a pendulum, the amplitude is the curved surface displacement or the horizontal displacement only?

Also, how is radius equal to the amplitude or displacement in a pendulum?! Shouldn't it be the circumference???
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6 years ago
#2
http://www.thestudentroom.co.uk/show...php?p=47008938
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#3
(Original post by Stonebridge)
http://www.thestudentroom.co.uk/show...php?p=47008938
That does clear a lot of clouds but my book also says that the radius is equal to the displacement or the amplitude which completely confuses me. I understand if the angle is taken as a measure or the kind of horizontal displacement that rjs123 took but radius!? That does not go into my head!
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6 years ago
#4
That does clear a lot of clouds but my book also says that the radius is equal to the displacement or the amplitude which completely confuses me. I understand if the angle is taken as a measure or the kind of horizontal displacement that rjs123 took but radius!? That does not go into my head!
You need to give more information about what your book actually says and what, exactly, it is describing. I suspect you are confusing this with something else.

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#5
(Original post by Stonebridge)
You need to give more information about what your book actually says and what, exactly, it is describing. I suspect you are confusing this with something else.

I'm referring to the IB Pearson HL book. In order to explain how the equation for SHM are derived, the use a pendulum that is moving in circular motion.

This is the diagram that we have for displacement or amplitude, that is causing all the confusion.
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#6
Ok, so the diagram isn't coming any bigger than this on TSR so I'll explain it...
The hypotenuse is x0. Then there's theta, the angle and the horizontal is "x0 cos theta" and the vertical is "x0 sin theta"

And the coloured ball is the bob...
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6 years ago
#7
Why is the pendulum not hanging downwards?
Are you sure this diagram is about a swinging pendulum?
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#8
(Original post by Stonebridge)
Why is the pendulum not hanging downwards?
Are you sure this diagram is about a swinging pendulum?
It is surely about a pendulum moving in circular motion. The model of the pendulum moving in circular motion is then used to derive equations for the pendulum moving in SHM.
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6 years ago
#9
It is surely about a pendulum moving in circular motion. The model of the pendulum moving in circular motion is then used to derive equations for the pendulum moving in SHM.
You are confusing the word "pendulum".

Your original question about a pendulum implied (to me at least) a mass on a string that swings from side to side. You were asking about its amplitude. The thread I referred you to explained that.

But you seem to be talking about something completely different.
A pendulum doesn't normally "go round in a circle".
You can describe SHM by considering motion in a circle (this is a mathematical model) but this is not a "pendulum".
On the other hand, a real pendulum, a swinging mass on a string, does undergo SHM if the oscillations are small.
I think you are confusing two different ideas.
0
#10
(Original post by Stonebridge)
You are confusing the word "pendulum".

Your original question about a pendulum implied (to me at least) a mass on a string that swings from side to side. You were asking about its amplitude. The thread I referred you to explained that.

But you seem to be talking about something completely different.
A pendulum doesn't normally "go round in a circle".
You can describe SHM by considering motion in a circle (this is a mathematical model) but this is not a "pendulum".
On the other hand, a real pendulum, a swinging mass on a string, does undergo SHM if the oscillations are small.
I think you are confusing two different ideas.
Oh yes... I get it... thanks!! 0
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