Need Help With A Math Calculation

**Perlmudder** · 10-13-2009 05:27 PM

So I have done this a bunch of times before, but for some reason I cannot figure it out this time. I am taking a coastal processes class and we are studying waves. I keep using the same formula, but the output just does not seem correct. I keep getting random numbers, and it just is not working for me. The formula we are given is:

Length = gT^2/2pi

where
g = gravity = 9.8
T = frequency
pi = 3.14....

So if wave 1 has a height of 10cm and a frequency of 0.75, what is its length?

So if wave 2 has a height of 12cm and a frequency of 0.87, what is its length?

So far I keep getting wave 1 = 20cm and wave 2 = 25cm. I am almost 100% positive these numbers are incorrect.

Soooo anybody good with math?

**DollaBill** · 10-13-2009 06:02 PM

Cig Daze will most certainly have your answer

**Dude! Sweet!** · 10-13-2009 06:11 PM

The answer is most certainly "69". It is always "69".

**Perlmudder** · 10-13-2009 06:28 PM

What confuses me even more is that we need to solve for the waves length, yet we don't even need the height of the wave.

**Shockwave** · 10-13-2009 06:34 PM

Set drives at 3 , tabs at 2 and mash the throttles.
Then wait for fuel to empty .

**jmeng** · 10-13-2009 06:38 PM

Are you sure one of the 2s in the exponent isn't actually a z for height. The 2s cancel out, why wouldn't they just write the exponent as 1/pi?

**Perlmudder** · 10-13-2009 06:47 PM

Originally Posted by jmeng

Are you sure one of the 2s in the exponent isn't actually a z for height. The 2s cancel out, why wouldn't they just write the exponent as 1/pi?

Thats what I thought. But I looked back at an old assignment, and the thing that made the formula work was that we had a frequency of 10 seconds, not 0.75. It just isn't making sense anymore. The numbers are to small.

**Dude! Sweet!** · 10-13-2009 06:56 PM

I'm 50% in agreement with Schockwave, although his Cig is probably too heavy since I'd set the tabs at 3 and then just trottle it...

The more important quesiton is what board would you ride on a 12cm wave? 12cm is what, like 7 feet? Jeeze? Dang catards and their so called metric system.

And for the record, I'd go with an asymetrical "gun". Maybe 9'6"?

**Dude! Sweet!** · 10-13-2009 06:58 PM

Originally Posted by Perlmudder

Thats what I thought. But I looked back at an old assignment, and the thing that made the formula work was that we had a frequency of 10 seconds, not 0.75. It just isn't making sense anymore. The numbers are to small.

Now we're getting into some sort of "unified" theory sh*t! Big bang vs molecular...

Good luck Joshie-baby! I'll have another captain and coke and think on it some more!

**03darkshadow** · 10-13-2009 07:53 PM

im tarded

maybe 5.5 for the 1st one?

**03darkshadow** · 10-13-2009 08:18 PM

this may help

http://www.coastal.udel.edu/faculty/rad/wavetheory.html

**Seafordguy** · 10-13-2009 08:18 PM

Wave 1 has a length of 8.602039 and Wave 2 has a lenght of 11.57527 if you simply plug in the frequency to the formula but I am not sure how the height applies and I think that is important....

**Perlmudder** · 10-13-2009 08:52 PM

Originally Posted by 03darkshadow

this may help

http://www.coastal.udel.edu/faculty/rad/wavetheory.html

Thanks. I found that before when I searched google and it asks for depth and some other stuff we don't have. This stuff is just to frustrating.

**Perlmudder** · 10-13-2009 08:55 PM

Originally Posted by Seafordguy

Wave 1 has a length of 8.602039 and Wave 2 has a lenght of 11.57527 if you simply plug in the frequency to the formula but I am not sure how the height applies and I think that is important....

Ya, I got those also. The problem is they just don't sound right. I feel like the waves need to be in the 40-50cm range judging by the other waves we measured. These ones were just moving way to fast in the wave tank to estimate by eye.

**fund razor** · 10-13-2009 09:01 PM

I once faced the same problem.

So I changed majors.

**cigdaze** · 10-13-2009 09:19 PM

I don't see where height factors into the equation: Length = gT^2/2pi

Are you missing an "h?"

Also, Make sure your units are all consistant. If g is given in 9.8 m/s^2, then the other units must also be in meters (10 cm = 0.10m).

Is frequency expressed in radians/sec or hertz?

**Perlmudder** · 10-13-2009 09:34 PM

Originally Posted by CigDaze

I don't see where height factors into the equation: Length = gT^2/2pi

Are you missing an "h?"

Also, Make sure your units are all consistant. If g is given in 9.8 m/s^2, then the other units must also be in meters (10 cm = 0.10m).

Is frequency expressed in radians/sec or hertz?

Thats what is getting me. There is no h in the formula. I have used it before, and it gave me the correct answer, but this time, using frequency (which is in hertz) it just is not working.

**phragle** · 10-13-2009 09:45 PM

ok..since I have never even contemplated learning this, I am assuming a couple of things
1. freq is red, wave height is blue.
2. pi is in the equation because if you count the arc from crest-midline-trough-midline-crest you have 360 degrees of total arc. is wave length the length of the surface (if you stretched the wave out length wise and measured it?

if this is the case, by calculating the circmfrance of the circle created by the wave would give you wave length....

Though I am probably completely wrong...

**phragle** · 10-13-2009 09:50 PM

the 0.75, does that mean that from beginning to end is 3/4 of a second?

**fund razor** · 10-13-2009 09:58 PM

Hey Phragle... draw it again using lake erie waves.

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