You are Here: Home >< Physics

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

1. 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 ), 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 ?

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 ?

2. bump
3. Take a look at this thread
http://www.thestudentroom.co.uk/show....php?t=2323508
4. (Original post by Stonebridge)
Take a look at this thread
http://www.thestudentroom.co.uk/show....php?t=2323508
Thanks

Well I ended up changing them today and made up my results so that it looks like I've measured the amplitude in the horizontal, just to play it safe!
5. (Original post by Stonebridge)
Take a look at this thread
http://www.thestudentroom.co.uk/show....php?t=2323508
Hi Stonebridge... two very quick questions !

“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 ?

Thanks
6. (Original post by posthumus)
Hi Stonebridge... two very quick questions !

“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 ?

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
7. (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!
it was lnA against t graph so I guess it's inversely proportional then !

Thanks a lot appreciated.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: April 23, 2013
Today on TSR

### Falling in love with him

But we haven't even met!

### Top study tips for over the Christmas holidays

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.