How to get points that intersect the trendline?

Basically I did the Cavendish experiment, and I have a damped sinusoidal wave plotted o开发者_JAVA百科n Excel. With Position (mm) against Time (s).

My problem is that I have added a tread line through the wave function, and wish to calculate the points of which the wave function intersects the tread line. From this I will then be able to calculate the time period.

At the moment I'm just having difficulty getting the intersects..

Thanks

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Excel is probably not the best tool to do what you want. In general, you want to fit your data to a damped Sin() function, e.g., F(x) = (A - B x) Sin(C x) or F(x) = A exp(-B x) Sin(C x), for linear or exponential dampening. Fitting the curve to the data will give you the values of the constants A, B, and C that fit the data best, and you can then proceed to simply solve F(x) == f_tread(x) to get the values x of intersection.

Programms like Mathematica, Matlab, or the free python based Sage are ideal for this and you can do it literally with two lines (well maybe three if you need to import the data first :-) ). I highly encourage you to give them a try if possible.

If you want/have to use Excel, then you can use it in a similar way for the data fitting part to get the constants A, B, C, etc. However, the part of finding intersections is trickier and unless you want to find the intersections by hand, you probably have to use an add-in like Solver and VBA script.

Finally a third way (since you seem to already have the formula for the damped sin wave) is to just plug the F==tread equation into WolframAlpha like so.