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hi guys today I would like to talk to you about a lab that we are going to do it's a virtual lab

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and we are going to use a tool or for that lab that is called fed that you can find on the

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internet okay but before starting with the lab I would like to remind you any different things

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about the Hooke's law so as you know or you should know Hooke's law describes the

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elastic behavior of materials okay so if you have a spring like here you have a

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spring hanging from the ceiling this is the ceiling okay when the spring is

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without nothing hanging from it this has a length okay we are going to to mark

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this point that the spring reaches and if we hang a mass from the spring the

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spring is going to stretch to a different point so it's going to stretch

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this distance okay and that distance is what we call the elongation or X so X is

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the elongation okay well the point is that when you exert a force on the

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screen the screen stretches and the elongation is directly proportional to

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the force that we exert on the screen okay and we can write that with an

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equation that's that stages that the course that we exert on the screen

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equals a constant times the elongation of the spring okay so this constant

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this constant depends on the spring if the spring is very weak

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the constant is small if the spring is very strong okay the

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constant is large right well so this is Hooke's law that states that the

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deformation or elongation of the of the screen when you exert a force on it is

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proportional to the force and the constant of proportionality is this K

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that it depends on the screen it's different for each different screen okay

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now this is if we are pulling with the force but if we hang the mass from the

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spring the force is going to be the weight okay so in this case that we are

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drawing here the force equals the weight of the mass okay and the weight is P

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equals the mass times D okay now a reminder about the units that we are

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using okay so as x is a length we use meters as f is a force we use newtons and the constant will

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be measured in newtons per meter okay and in this case the weight is a force i remind you that the

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weight is different from the mass so the weight is a force is a newton the mass is in kilograms

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And the g, that is the constant of gravity, that is an acceleration, is in meters per

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second squared.

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This, in fact, on the Earth, on the surface of the Earth, is 9.8 meters per second squared.

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Okay, so what we can do is use these two equations, so that we take this equation and this equation

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and putting them together

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we know that the force equals the weight

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we can say that the force is the mass

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times the g

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which equals

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the constant

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times the elongation

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ok

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so if you have

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if the unknown is the constant

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you can pass the x

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to the left side

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dividing

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ok

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so you pass this

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to this side dividing to isolate the constant and then in that case you

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obtain the constant equals M times G over X and this is the first equation we

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are going to use in the lab. Second part, imagine now that

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the unknown is the mass so you want to isolate the mass then you will pass this

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to this side and you will obtain that the mass equals the constants the

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constant times the elongation over the acceleration of the gravity so we are

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going to use these two equations in the following slides so this is equation

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number one and this is equation number two so we go with equation number nine

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number one sorry that says that the constant equals the mass times the

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duration of the gravity over the elongation and then is when it appears

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the script of the lab that we are going to do I'm going to show you the script

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okay and I'm going to show you the tool that we are going to use for the lab and

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And then I will come back to this board to continue with the explanation. Okay? So, let me change or switch this to the PDF that we are using.

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okay so you will find in the instructions for the assignment that you

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have to hand in this PDF with different with the script for the practice so you

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have an introduction this introduction is basically what I have explained to

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you about Hooke's law okay and then you have a picture that if you click on the

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future you will go directly to this web page where you have this but this is

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like they said in a lab mean that you are in the lab in the school okay so you

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can work with the lab and take measures just by doing it quickly okay and the

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first thing that we will do in the lab is to fill this table and try to analyze

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what is happening okay so we have to use different masses okay and depending on

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the mass we are going to we know that that mass is related to a to a weight

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okay and we will analyze the displacement and try to calculate the

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spring constant I'm going to show you what how so if we click on this okay we

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will go to the page I'm going directly to the page where we are going to work

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with lab okay so when you click on that page you will find this simulation okay

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these three boxes on the right are more more advanced so we are going to use

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only the intro box ok so you click on it and then you find this lab setting ok

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you have two different springs we are going to use only the one on the left

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right and we are going to set depending on the instruction for different tables

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maybe small you see when I move the spring constant to small is very thin

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the wire or if I move the slide to large it is very thick okay so this is a

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stronger spring and when it's asked to be done in the center you can choose

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maybe one two three four in the fourth point and it's something in between okay

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so we are going to set it to small okay and then we want to mark the equilibrium

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position so if you go to the box on the right you can click on the equilibrium

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position and you will find the line and natural length and you will find the

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line so this is the natural length and the equilibrium position will appear when I

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hang a weight from the screen so imagine that I start with the 50 grams

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weight if I hang it you see that this is the equilibrium position that is going to

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reach but if I stop holding it it's going to oscillate okay because that's

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when you hang something from a screen okay so if we want to stop the

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oscillation you see that there is a red light on the left if you click on that

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red light it's going to simulate the position when you when you stop the

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screen and it will stop in the equilibrium position okay that's right

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and now the point is that we distance from this point the blue line to the to

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the dashed green line is the elongation the X and we want to measure that

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elongation so we have a ruler so if we put the ruler with the zero on the blue

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line you can find that this is going to be 16 and these are centimeters so 16

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centimeters is the elongation for this first weight okay so I'm going to write

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it down because later on we are going to complete the table so we have 16 grams

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for the mass of 16 centimeters sorry for the mass of 50 grams okay then we're

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going to make a second measure with this second mass is 100 grams so it's

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oscillating again if I click on the red light I will stop the oscillation okay

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that's it and then you see that the for the mass of 100 grams we obtain a length

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of 32 centimeters okay well we want to express the masses in kilograms so the

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mass 50 well I'm going back to the board to continue playing you with

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these two measurements that we did so we come back to the board okay here we are

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okay so we did we started with the mass of this mass okay zero point zero five

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kilograms this is the same as the mass of 50 grams okay if you convert this

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into kilograms right 50 grams converted into kilograms we divide by grams

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multiplied by kilograms 1 over 1000 we get rid of the grams and we have 0.05

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kilograms okay okay we know that the gravity is 9.8 meters per second square

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and this is this is the same for any of the measures that we are going to make

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because we are on the earth okay and I will let this for you okay what is the

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weight the weight is in Newton so to calculate the weight we M times nine

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point eight okay so we multiply these times these we obtain the weight so if

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we do that we have point zero five times nine point eight this is zero point

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49 newtons okay what is the displacement before the first we obtained a displacement of 16

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centimeters but we want to have this in meters right because it's the unit in the international

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system so we convert it so one meter is 100 centimeters we get rid of the centimeters

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and this 0.16 meters and then we obtain the spring constant this mg the weight

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we can write this as p over x okay so the constant is going to be p over x so the first constant

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first constant is going to be the weight 0.49 newtons over 0.16

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meters okay if we calculate that you see that is 3.06 newtons per meter

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okay we will do the same for the second and if you do this the same for the

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second you will obtain a different value. Imagine that you obtain 3.07

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I say imagine okay so maybe you obtain a different thing okay then you have to

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calculate the average here so you have let's say constant 1 constant 2 and

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constant 3 and this is the average the average would be constant 1 plus

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constant 2 plus constant 3 over 3 and when you calculate this this is the

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average that you're going to write here okay so that's what you'll do

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to complete and calculate the constant of the string you see that this first

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table is when you when you set the constant to small now we are going to

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check uh well you will have to complete all the two tables with the constant between small and

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large and finally one with the constant to large and then if we go to the other the second table

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that we have to complete the second table we have to calculate the mass okay so if we

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come back to the first page you see that we have that the mass is the constant constant times the

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elongation over the g so the mass is the constant times the elongation over the g okay we are going

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to come back to the lab tool to check the different things that we need for this um

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for this lab i remind you that if we set the constant too small we obtain a 3.06 newtons per

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meter meter meter constant so we can bring this with a second where is my

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board okay so the constant I was saying that if it's three point zero six so we

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can bring three point zero six Newton per meter okay and then we go now to the

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to the tool right so we go to okay and now we left this here we have three

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different weights in here that we don't know what is the mass of those weights so

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you check that you have the spring constant maybe in small for

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example to use the constant of the of the spring with small and then we put

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this weight in the spring we stop the spring and then we measure we measure

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that is 24 okay so 24 centimeters right so then we come back to the board so we

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said that is 24 so the displacement is 24 centimeters which if you make the

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conversion is 0.24 meters this is 0.24 meters okay so well if you want to

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calculate the weight the weight the weight is M times E equals K times X so

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if you multiply this times this you are going to get to get the weight right

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for the mass color was pink, I think. Pink for the mass. So the force or the weight

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is going to be this times this, so 3.06 times 0.24. This is 0.73

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Newton. We know that the gravity is 9.8 meters per second square and the mass

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that is the last thing that we have to calculate is the weight divided by the

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G so in this case it's going to be 0.73 Newton over 9.8 meters per

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second square and we will obtain a mass from this point it is over 9.8 this is

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0.075 kilograms or in grams is 75 grams okay but we have to write it in

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kilograms so 0.075 kilograms right and it is this is the weight how you are

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going to complete this second table okay and then finally in this group if we

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come back to the period okay so we have the first box with the constant set to

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small then we have a second table halfway between small and large then a

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first string with and set to large okay this is the third and then with the one

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that we are going to use to calculate the different masses you have the

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equations here okay I make you aware that in English the weight we are using

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P because it's how it appears in your book but in English we have W for weight

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okay and finally you have to check or write choose different words in this

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sentence to be sure that you understood the laugh as you understood the hook

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flow and that's all guys so you have any question don't hesitate to send me a

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message or write a question in the forum or in the virtual classroom okay so see

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you soon bye