Science Buddies: "Ask an Expert"

Hello, for my upcoming science fair I am considering doing the project Deep Knee Bends. Although I am not a dancer and believe it would be strange for me to do a project that has to do with the angles related to dance positions (Demi plies). I am really interested in this project though, therefore I was wondering if the project could be related to something else? Or does it even make sense to just have it based on simply bending your knee? Also Im a volleyball player, so I do a lot of jumping and landing in bent positions, does this have anything to do with the project or can I relate it to the project in some way?
Thanks for your help.

Hello there,

Of course it's okay to steer this project in a different direction, especially to something that interests you more! Part of the fun of science projects is to design an experiment based on questions you're interested in, or modifying previously done experiments to address new ideas. You can certainly try a number of different angles for the knee bend and measure the tension. You can even look at the different jumping and landing bent positions that you do in volleyball, determine the angles at which they occur, and test these angles with your model knee to see how it affects the tension. Feel free to write back with more details as you're brainstorming and planning your experiments, and we'd be glad to help you out.

Connie

Thank you for the reply it was very helpful I will let you know for sure if I have any questions in the future as a start my project.

Hello,
I have decided that I will keep it simple and do the normal project for the experiment, although I'm having a little trouble with some materials. For this project you have a mechanical model (mainly made of wood and hinges) that represents a simple version of the human knee. This model is used to identify the amount of stress put on your patella when bending at different angles. I have a majority of the materials but I'm having a little trouble with finding the springs. In this project the springs are used to represent the quadriceps muscle and you will be using two different springs. I have looked to find these specific springs and simply had no luck. If I were to go with a similar spring which measurement should I for sure keep the same? Ex. Length, width, gauge? Thanks for your help.
Kylie

Hey there,

It's probably fine that you can't find a spring with the exact same dimensions as mentioned in the procedures. I don't think it's necessary to keep the length, width, or gauge the same, but I could be wrong. If other experts have a better idea, please give us your input! I would also maybe post this question on the physical sciences forum as well because there are probably physicists there who understand a lot better than I do about how springs work and may give you some advice on what you should purchase and how to go through the experimental procedures.

Sorry that I can't be of more help, but let us know if you have any other questions!

Connie

Hello,
For my upcoming science fair I have decided to complete a project on this website called Deep Knee Bends. It is a basic test, using a mechanical model of the knee, to measure the amount of stress put on your patella and patella tendon at various angles. I am completing my research at the moment and so far have had little problems besides the materials. Currently I am looking for the mechanical model materials. I have a majority of the materials but I'm having a little trouble with finding the springs. In this project the springs are used to represent the quadriceps muscle and you will be using two different springs. Which I think represent strength of your quadriceps muscles?? I have looked to find these specific springs and simply had no luck. If I were to go with a similar spring which measurement should I for sure keep the same? Ex. Length, width, gauge? Thanks for your help.
Kylie

Hi Kylie-Brez,

I'm sorry to hear you are having a hard time finding the springs for this project. I did some checking online, and found that searching for "wire extension springs" brought up helpful results. There is a company called Forney that has sells springs that could work for this project (https://www.forneyind.com/store/results ... ory_id=627). I've never ordered from that company, so I can't recommend them; I'm just saying that it looks like they sell these kinds of springs.

That being said, it looks like the most important parameter is the length of the spring, followed by the gauge of the wire. If the spring is much longer or shorter than the dimensions given in the materials list, the spring will either be too long or not reach far enough to attach properly to the "leg". If the gauge of the wire is too thick, the spring will be very stiff. It doesn't look like diameter is as important a factor as length and gauge, but I probably wouldn't use, for example, a 2" diameter or a 1/8" diameter spring.

Post back if you have other questions.

Hi Kylie-Brez,

Terik's recommendation seems like a good one. From experience I can also recommend a company called McMaster-Carr, which has a huge selection of springs that you can narrow down by length and wire diameter:

http://www.mcmaster.com/#springs/=uxnx3g

If that link doesn't work, just go to www.mcmaster.com and search for "springs".

Hello. We noticed you had two different threads going for the same topic. We merged the two into a single thread. Please keep all questions to one thread so that our experts can best help you based on what has already been discussed.

Good luck, and thanks for using Science Buddies!

Hello everyone,
Thank you all for the helpful tips that is exactly what I needed! Two more quick questions though. What material would you recommend using for the spring? And in the materials list it asks for two different springs, what exactly do the two different springs measure? Is it the tightness of the quadriceps muscle?

Thanks for your help
Kylie

Hi Kylie,

1. Regular steel should be fine for your spring. You don't need stainless steel since your experiment probably won't be getting wet. If you are ordering from McMaster, I would just use the menu options on the left to narrow down the dimensions of the spring (as described in the Materials list).

2. Looking at step 6 of the procedure under "Measuring Tension Using the Model Knee", it says "Replace the "quadriceps" spring, and repeat the experiment." So, I assume that means you do the whole experiment with one spring, then you repeat it with the other spring, and compare your results as described in the rest of the procedure. Since the two springs have different dimensions, they will have different stiffnesses - so you're correct that, in this model, they simulate different tightnesses of the quadriceps muscle.

Good luck!

Hi bfino

Thanks so much for your help, that cleared up a lot of questions for me!

Kylie

Hello again everyone,

I am in the results stage of my project and I am needed some help.
As I am only in 9th grade I have not yet studied physics or hooke's law. With this, I am having quite a bit of trouble with the formula. I have conducted the experiment and my results, although, I am unable to and confused with finding my constant value (k). Could anyone guide me in the right direction starting with what information I will need from my experiment (length stretched, length at rest, difference)? As well I was wondering if I could get some help with graphing the data to help find the slop? If that is correct? Just in general I was wondering if someone could explain to me how to find the constant for this particular project?

Thank you to anyone who is willing to explain this to me.

Hi Kylie,

It might help if you look at this reference page we have on springs:

https://www.sciencebuddies.org/science- ... earsprings

Particularly, look at equation 2 on that page:

F = k(x-x0)

and the graph in Figure 3. You should be able to make a plot from your data with the difference between the spring's stretched length and rest at length (the "x-x0" from Equation 2) on the x-axis, and force on the y-axis. The slope of that graph is your spring constant, k.

Have you learned about graphing lines in math class (usually math classes use the equation y=mx+b)? If so, that might help you understand.

Thank you for the website, it did help quite a bit. Although, now I am stuck with one question. From my understanding I will need the force to figure out the constant and the constant to figure out the force, expect I do not have either?? Currently for information that I can fill in my formula all I have is the difference of the spring (x). I do not understand the fact that if I am doing the experiment to try and figure out the relative force, how would I find it with the formula given?

Hi Kylie,

I apologize, as I hadn't completely read the project's procedure in detail. I thought it actually had you measure force somehow, but it looks like you're correct - all you have is displacement. Step 7 says:

"For each spring, make a graph to show the length of the spring (y-axis) as a function of angle of the knee joint (x-axis). Remember that according to Hooke's Law, the force in a spring is directly proportional to its displacement from equilibrium (or its length at rest). So, even though you are not calculating force directly, you can still see the relative levels of force at different knee angles by creating a plot of spring displacement vs. knee angle. If you would like to calculate force, first you will need to measure the k value for your spring (see the Background tab)."

So, if all you want to do is see the RELATIVE levels of force, you are OK with what you have. If you want to calculate the actual force, you need the k value for the spring.

Do you have links to where you bought the springs? You may be able to look up the k-value from the manufacturer, which would save you from measuring it yourself.

-Ben