# Using Log base 10 to find gravity

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How can i use log base 10 to plot a graph and find the gravity value for this question.

I am thinking take the log of both sides and plot the log (T) on y axis and log (L) on the x axis and using the gradient to find value of gravity. But taking the log of T gives me a negative number so i was thinking of taking log of T^2. I dunno for sure.

Hoping some of you people who are more comfortable with logs would be able to explain better.

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#2

(Original post by

How can i use log base 10 to plot a graph and find the gravity value for this question.

I am thinking take the log of both sides and plot the log (T) on y axis and log (L) on the x axis and using the gradient to find value of gravity. But taking the log of T gives me a negative number so i was thinking of taking log of T^2. I dunno for sure.

Hoping some of you people who are more comfortable with logs would be able to explain better.

**Jyashi**)How can i use log base 10 to plot a graph and find the gravity value for this question.

I am thinking take the log of both sides and plot the log (T) on y axis and log (L) on the x axis and using the gradient to find value of gravity. But taking the log of T gives me a negative number so i was thinking of taking log of T^2. I dunno for sure.

Hoping some of you people who are more comfortable with logs would be able to explain better.

The gradient will be from which it should be easy to find .

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(Original post by

Plot a graph of (square of time period) against (length), this will be a straight line.

The gradient will be from which it should be easy to find .

**Zacken**)Plot a graph of (square of time period) against (length), this will be a straight line.

The gradient will be from which it should be easy to find .

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#4

(Original post by

I have already done that once. But i need to use log base 10 to tackle this question.

**Jyashi**)I have already done that once. But i need to use log base 10 to tackle this question.

So plot against , it should have gradient and then investigate the y-axis intercept.

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(Original post by

Fair enough. Take the logarithm of both sides:

So plot against , it should have gradient and then investigate the y-axis intercept.

**Zacken**)Fair enough. Take the logarithm of both sides:

So plot against , it should have gradient and then investigate the y-axis intercept.

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#6

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Yes but when i take log T i get a negative number. Is it ok for time to have a negative number? The same thing happens with log L. So i was thinking of doing log (T/2pi). Dunno if it will work.

**Jyashi**)Yes but when i take log T i get a negative number. Is it ok for time to have a negative number? The same thing happens with log L. So i was thinking of doing log (T/2pi). Dunno if it will work.

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(Original post by

Time is not negative, the logarithm of time is. And that's fine, nothing wrong with that.

**Zacken**)Time is not negative, the logarithm of time is. And that's fine, nothing wrong with that.

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#8

(Original post by

But i will plot the negative values on the negative y and x axis right?

**Jyashi**)But i will plot the negative values on the negative y and x axis right?

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(Original post by

Yeps.

**Zacken**)Yeps.

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(Original post by

Yeps.

**Zacken**)Yeps.

Ok so i get this graph where the intercept looks like 0.302.

I see that 1÷2 is the gradient and the intercept represents the 2pi/sq g. So does this mean that i should reformulate g = sq (2pi/0.302)?

I see that 1÷2

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#11

(Original post by

Ok so i get this graph where the intercept looks like 0.302.

I see that 1÷2 is the gradient and the intercept represents the 2pi/sq g. So does this mean that i should reformulate g = sq (2pi/0.302)?

I see that 1÷2

**Jyashi**)Ok so i get this graph where the intercept looks like 0.302.

I see that 1÷2 is the gradient and the intercept represents the 2pi/sq g. So does this mean that i should reformulate g = sq (2pi/0.302)?

I see that 1÷2

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(Original post by

The intercept looks negative, no? And the intecept requires log (2pi/rt(g)). So you'll need to take the exponential.

**Zacken**)The intercept looks negative, no? And the intecept requires log (2pi/rt(g)). So you'll need to take the exponential.

So i take e^-0.2 = 2pi/sq g ?

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#13

(Original post by

Ah yes its -0.2 but i just read the equation of line and shut my brain after that lol.

So i take e^-0.2 = 2pi/sq g ?

**Jyashi**)Ah yes its -0.2 but i just read the equation of line and shut my brain after that lol.

So i take e^-0.2 = 2pi/sq g ?

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(Original post by

Yep! Although something has gonewrong somewhere because that's a horrible estimate of g, I'm not sure what though. Hopefully someone whose brain isn't completely fried will jump in.

**Zacken**)Yep! Although something has gonewrong somewhere because that's a horrible estimate of g, I'm not sure what though. Hopefully someone whose brain isn't completely fried will jump in.

Hopefully an advanced alien civilization can recover this forum thousands of years in the future and find out the answer to this paradox which was clearly the limit of human intelligence.

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#15

(Original post by

Something has gone wrong somewhere. I see grahically the intercept as negative but when i feed in the x and y values to work out c algebraically the intercept always comes out to 0.3

Hopefully an advanced alien civilization can recover this forum thousands of years in the future and find out the answer to this paradox which was clearly the limit of human intelligence.

**Jyashi**)Something has gone wrong somewhere. I see grahically the intercept as negative but when i feed in the x and y values to work out c algebraically the intercept always comes out to 0.3

Hopefully an advanced alien civilization can recover this forum thousands of years in the future and find out the answer to this paradox which was clearly the limit of human intelligence.

Ensure you are using the correct units

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(Original post by

The intercept should be 0.3. 0.3 is correct. Check you have not plotted your data using the incorrect column

Ensure you are using the correct units

**Student403**)The intercept should be 0.3. 0.3 is correct. Check you have not plotted your data using the incorrect column

Ensure you are using the correct units

This is why we need the aliens.

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#17

Ignore my above post

Your intercept of 0.302 is correct. Zacken watch out Intercept of -0.2 is where x = approx (-1), not where x = 0

See the x axis labels

Anyway the second reason you were not getting the correct value of g is because of the base.

Now that you have 0.302 as your intercept, you need to be taking 10 to the 0.302, not e to the 0.302

So with 10^0,302 = 2pi/sqrtg

You can solve to get g correct to 2 S.F.

Your intercept of 0.302 is correct. Zacken watch out Intercept of -0.2 is where x = approx (-1), not where x = 0

See the x axis labels

Anyway the second reason you were not getting the correct value of g is because of the base.

Now that you have 0.302 as your intercept, you need to be taking 10 to the 0.302, not e to the 0.302

So with 10^0,302 = 2pi/sqrtg

You can solve to get g correct to 2 S.F.

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#18

(Original post by

Now that you have 0.302 as your intercept, you need to be taking 10 to the 0.302, not e to the 0.302

So with 10^0,302 = 2pi/sqrtg

You can solve to get g correct to 2 S.F.

**Student403**)Now that you have 0.302 as your intercept, you need to be taking 10 to the 0.302, not e to the 0.302

So with 10^0,302 = 2pi/sqrtg

You can solve to get g correct to 2 S.F.

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(Original post by

I cant see an error. I have plotted log (L) on x axis and log (T) on the y axis and they are correct to the right decimal points.

This is why we need the aliens.

**Jyashi**)I cant see an error. I have plotted log (L) on x axis and log (T) on the y axis and they are correct to the right decimal points.

This is why we need the aliens.

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#20

(Original post by

Bloody hell, literally just realised I was using the wrong base!! Argh, too much pure maths for me. Thank you!!

**Zacken**)Bloody hell, literally just realised I was using the wrong base!! Argh, too much pure maths for me. Thank you!!

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