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In this video, I'm going to revise what we have done today in class.

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I'm going to teach you how to find the equation for a certain law,

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starting with a table of data, like the ones that you have found for the period and the length.

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Thanks to Javier Pinel, who provided with this data, that are very good.

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And this is where we need to start.

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I also will need a calculator, here I have one,

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and a ruler to make the graph as good or as nice as possible so I'm going to

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start by making the graph okay so I'm going to put like the ruler here this is

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going to be sorry about that okay this is going to be the x-axis I use the

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ruler now I'm going to use it again to write or to create to draw the vertical

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axis okay so these are the vertical and the horizontal axis that we need or

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we also need always need in the graph next I'm going to write the length in

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the horizontal axis and I need to remember this of the length is going to

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be here okay and the period that is symbolized by a capital T is going to be

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on the vertical axis this is the period is measured in seconds I need to choose

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the scales I'm going to start here for example is going to be I'm not don't

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need to start with zeros I'm going to start with 0.7 meters here this is going

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to be 0.8 0.9 and finally one meter okay this is this is the information that is

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provided here in the first column of the table. Then in the vertical axis I'm

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going to represent the period. Starting, for example, I'm going to start here like

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this is 1.9. Notice that it's not necessary that I start in the 0, 0. I can

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start or my origin can be other point. The important thing is to use as much of

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the space as I can. Then this is 1 and let's say this is going to be 2, 2, 1, yes.

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and do like this is 2.0 2.1 2.2 2.3 and sorry this is for 2.2 again 2.2 is 2.3

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and it's a little bit and this is 2.4 I'm going to take this out I want to

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make it nice okay so this is going to be two point four seconds seconds and I

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remember the period is here and now I need to plot the points of the table so

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zero point seven corresponds to a period of one point and almost two so she's

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zero point seven is here almost two it must be around here okay this is my

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first point of the graph, my first plot of the graph. Next is 0.8, 8 is 2.1 and a

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quarter. So this is 0.8, 2.1 and a quarter must be around here. So this is my

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second point 0.9 match with 2.25 2.25 2.2 25 is exactly this line between 2.2 and

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2.3 and finally 1.0 matches 2.372 that is more or less here between 2.5 and

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and 2.4 as you can see the points are almost in a straight line particularly

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this they are in a straight line okay we can see this okay it's a very good set

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of data so we can even write this draw a straight line but I want to make it nice

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and I don't know how it doesn't work okay so we have kind of a straight line

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and now as it is a straight line we can say that the period and the length is

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proportional so we can say that our law has going to be a formula like this the

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period is proportional to the length and what you need to do is to find which

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number is this constant this K is called the slope the bigger the slope the more

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inclined is the is a straight line to find the decay to find the constant we

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have to work out this kind of equation if we I'm going to take this out I don't

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need it anymore so to find K if you work out this

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equation you will see that the constant K is the period divided by the length so

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we are going to go to this table and in this table using the same I'm going to

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write the constant for each pair of values I'm going to start for example

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with 0.7 and 1.985 so I go to my calculator and the constant is 1 point

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sorry I had to change the version the constant is one one point nine eight

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five divided by zero point seven so this is my first value of the constant I'm

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going to write I have four the same three decimals here four figures I have

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one here. I'm going to set it in the middle. I'm going to use three.

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For this set of values 2.84. The constant has units as the

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period is seconds and the length is meters. This is seconds times meters. So we can

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write the units of the constant as seconds times meters. We can do the same

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with the next pair of values, I mean, 2.125 divided by 0.8 and you can see that the constant

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is not exactly the same but it's quite similar so 2.65 and the units are the

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same okay let's find the third value for the constant we divide zero sorry two

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point two point two five zero we divide this by zero point nine this number

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divided by this number okay and again the constant is not exactly the same but

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it's quite similar 2.50 and seconds per meter and to put this properly and I

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only have now one set one pair of values a length of one meter and this is very

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easy so the constant is 2.37 seconds per meter so these are the four values of the constant

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what is the real value for the constant we are going to do the average the average constant

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i'm going to do in a different color the average constant in spanish la media we calculate by

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By adding these four numbers, 2.84 plus 2.65 plus 2.50 and 2.37,

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another these numbers, divided by 4, because I have four total numbers.

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Ok, so we need to use our calculator now to do this, so is 2.84 plus 2.65 plus 2.50 plus

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two sorry plus two point thirty point thirty seven and we divide this number

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by four ten point this calculator works in a funny way so two point five nine two

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comma five nine is the average value of the constant. We will accept that as the

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real value. Don't forget the units. The units, remember, were seconds over meter.

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Okay? So now we can write the final equation for our experiment. The period

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is proportional to the length and the proportional constant the K is 2.54 okay

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this would be like our final result for our experiment I hope it helps remember

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you have to do the activity about the number of batteries and the intensity of

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of the electric current in a circuit okay class see you next day