Measuring amplitude of pendulum bob! HELP!!! :(

Hey guys,

Well today we were doing a practical... and we were required to measure the amplitude of an oscillating pendulum bob for each oscillation it did (I did it for 6)... the idea was that the amplitude is changing as it is being damped over time by air resistance.

Now... I measured the amplitude vertically (which was bloody difficult I assure you :frown:

), now I just realized the amplitude is typically measured horizontally!! & It is the maximum displacement in that direction. So have I done it wrong ? or very unreliably ? :frown:

I am pretty sure I will get (sort of) the same graph both ways... but I think it is extremely inaccurate as I'm taking extreme small readings compared to the bigger readings taken in the horizontal direction !

The graph by the way is "ln(A)" against "time displaced" (A=amplitude).

In the ISA, will I get penalized & lose marks for this ? :frown:

Thanks in advance!!

OP

bump

Take a look at this thread
http://www.thestudentroom.co.uk/showthread.php?t=2323508

Reply 3

posthumus

OP

20

Original post by Stonebridge

Take a look at this thread
http://www.thestudentroom.co.uk/showthread.php?t=2323508

Thanks

Well I ended up changing them today and made up my results :tongue:

so that it looks like I've measured the amplitude in the horizontal, just to play it safe!

Reply 4

posthumus

OP

20

Original post by Stonebridge

Take a look at this thread
http://www.thestudentroom.co.uk/showthread.php?t=2323508

Hi Stonebridge... two very quick questions ! :smile:

“Large number of values with the same absolute error" - could you explain what absolute error means ?

If I were to get a line with a gradient of -1 ... does that mean the relationship (of the y & x quantities plotted) is inversely proportional ? :smile:

Thanks

Reply 5

Stonebridge

13

Original post by posthumus

Hi Stonebridge... two very quick questions ! :smile:

“Large number of values with the same absolute error" - could you explain what absolute error means ?

If I were to get a line with a gradient of -1 ... does that mean the relationship (of the y & x quantities plotted) is inversely proportional ? :smile:

Thanks

The absolute error is the plus or minus value for the reading.
If you measure a length as 2.00 ± 0.02m the ±0.02m is the absolute error (or uncertainty).
This is different from the % error (uncertainty) which would be ±1% in this case.

A gradient of -1 will mean different things on different graphs.
On a standard y against x graph it means the relationship is y = -kx where k is a constant.
On a log graph it could mean y is inversely proportional to x, as 1/x is x^-1

Reply 6

posthumus

OP

20

Original post by Stonebridge

The absolute error is the plus or minus value for the reading.
If you measure a length as 2.00 ± 0.02m the ±0.02m is the absolute error (or uncertainty).
This is different from the % error (uncertainty) which would be ±1% in this case.

A gradient of -1 will mean different things on different graphs.
On a standard y against x graph it means the relationship is y = -kx where k is a constant.
On a log graph it could mean y is inversely proportional to x, as 1/x is x^-1

Ah wow you seem to know it all! :tongue:

it was lnA against t graph so I guess it's inversely proportional then !

Thanks a lot :biggrin:

appreciated.

Measuring amplitude of pendulum bob! HELP!!! :(

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