SherlockHolmes
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Is there a test you can use to see if a graph is logarithmic?

For example, to test for an exponential decay graph there is the half-life method.
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brianeverit
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(Original post by SherlockHolmes)
Is there a test you can use to see if a graph is logarithmic?

For example, to test for an exponential decay graph there is the half-life method.
If (a,b) is any point on the graph then (a^2, 2b) should also be on the graph ?
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SherlockHolmes
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(Original post by brianeverit)
If (a,b) is any point on the graph then (a^2, 2b) should also be on the graph ?
That doesn't seem to work on my graph. Perhaps it would be best if I showed you my data and graph.
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brianeverit
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(Original post by SherlockHolmes)
That doesn't seem to work on my graph. Perhaps it would be best if I showed you my data and graph.
Well that certainly doesn't look much like a logarithmic graph. It' s almost a straight line
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L'Evil Fish
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(Original post by SherlockHolmes)
That doesn't seem to work on my graph. Perhaps it would be best if I showed you my data and graph.
Assuming air resistance is negligible it'd be a straight line, but eventually if you get high enough it will level off (which would be terminal velocity)
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SherlockHolmes
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(Original post by brianeverit)
Well that certainly doesn't look much like a logarithmic graph. It' s almost a straight line
(Original post by L'Evil Fish)
Assuming air resistance is negligible it'd be a straight line, but eventually if you get high enough it will level off (which would be terminal velocity)
The graph is of exit velocity of water from a spouting cylinder against height of water level.

I am meant to analyse this graph but don't really know what to say. I thought at 0.2m and less it is tending towards the origin so assumed it was closer to a log graph than a straight line.
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L'Evil Fish
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(Original post by SherlockHolmes)
The graph is of exit velocity of water from a spouting cylinder against height of water level.

I am meant to analyse this graph but don't really know what to say. I thought at 0.2m and less it is tending towards the origin so assumed it was closer to a log graph than a straight line.
Well it's like log graph, but at what base.

How many marks for analysis?
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brianeverit
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(Original post by SherlockHolmes)
The graph is of exit velocity of water from a spouting cylinder against height of water level.

I am meant to analyse this graph but don't really know what to say. I thought at 0.2m and less it is tending towards the origin so assumed it was closer to a log graph than a straight line.
a log graph does NOT tend to the origin
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Chlorophile
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You can test if a graph is logarithmic by testing coordinates. If the graph is logarithmic, then \frac{log y}{x} will be equal (or close) to a constant for all coordinate sets.
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SherlockHolmes
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(Original post by L'Evil Fish)
Well it's like log graph, but at what base.

How many marks for analysis?
5/20 I think.

(Original post by brianeverit)
a log graph does NOT tend to the origin
I meant with transformations (translation, stretch etc).

(Original post by Chlorophile)
You can test if a graph is logarithmic by testing coordinates. If the graph is logarithmic, then \frac{log y}{x} will be equal (or close) to a constant for all coordinate sets.
I see. Then my graph is not logarithmic - thanks.
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