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So I made a post earlier in the year about my Extended Essay (http://www.teamliquid.net/blogs/viewblog.php?id=117246). I got a lot of responses (more than I was expecting) and I figured I might as well update you guys.
Well, to cut a long story short, the experiment failed. I procrastinated like a dumbass and when I finally got around to getting the data, it didn't show any sort of pattern.
So now with the extended essay due next week I'm kind of fucked. My new essay is about how heating up squash balls makes them bounce better (read: retain kinetic energy more efficiently). If anyone is interested/wants to help me out, details are in the spoiler.
+ Show Spoiler +So if any of you have played squash before, you'll know that the ball doesn't bounce that well. However, depending on the temperature of the room, the ball's behavior can change. That's what I'm investigating. My problem is, the experimental data is waayyyy too simple. It's literally a straight line graph. As the temperature of the ball increases, so does the bounce height. I'm assuming its because as the temperature increases, the amount of time spent touching the floor decreases, but it's not much more complicated than that. It's a directly proportional relationship, and there's very little advanced analysis here.
So in order to extend this (harharhar) a bit, I decided to focus specifically on the material of the ball, and how it gets affected by the temperature changes. I tested a table tennis ball by heating it up in the same way, and it showed basically no change in its bounce height. Therefore, I'm thinking that this relationship has a lot to do with the bonds and intermolecular forces and things like that. The squash ball is made of rubber, and bends easily. The table tennis ball is made of plastic, and doesn't. However, although I do know enough about chemistry to talk about that, is it delving too much into chemistry, and straying away from physics? I feel like I have to talk about it, but in order to do so, I have to compromise the focus on physics for the essay.
Furthermore, I feel like the experiment itself is a little too simplistic. This is something that could be done easily in a classroom (and was chosen specifically due to time constraints), and not really the "above and beyond" that the EEs generally tend to be. The IB physics EE guide specifically states that "Essays in experimental physics should cover topics not included in the school course’s regular investigations". Am I totally screwed, or is there some way to salvage this?
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Belgium9950 Posts
I think it's more an effect of the air inside the ball having more energy, thus inflating the ball more, decreasing the energy lost when the ball changes form when it hits the wall. Sure, the heat might have an effect on the rubber itself as well, but the majority of the change is gonna come from the increased inflation.
Now, if you're actually trying to make a university level physics essay, I doubt your teacher will answer with anything else than "duh" and flunk you.
I'm sorry..
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Eh. Stick with the same material ball, just change the temperature.
I'm thinking that the change in the rubber's spring constant can be neglected.
See how well you can approximate the bounciness as a function of temperature by modeling the internal pressure of the ball (approximately proportional to the temperature of the air inside, by pv=nrt).
If it's not complex enough, model the spring constant too. Using Young's modulus, apparently it's possible to show that the spring constant is proportional to temperature for certain materials.
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This exact issue was discussed in one of my material properties classes. I disagree somewhat with the above posts. I think the effect of a changing modulus would have a larger impact on the bounciness over these temperature ranges, when compared to the internal pressure. What you should find is that the bounciness vs temperature chart has a negative parabola shape to it. As you heat the ball the bounciness increases. However once you reach a certain point the bounciness begins to decrease again due to increased mobility of chains.
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United States24779 Posts
If you vary the temperature from below freezing all the way to pretty damn hot, it really is just a straight line plot? I find that somewhat hard to believe. Have you done enough research in to the material that the squash ball is made out of? That might give you ideas for which parts of your data to 'zoom in' on. Also investigating the air inside the ball like someone suggested sounds like a good idea.
I have no idea if this experiment of your will work for your class or not though. It's also kinda hard for us to help you with these since you never discuss your methodology for collecting data. Why did you football question fail? What was your method for collecting data?
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Ludrik claims it's not linear, but a parabola, which is pretty believable for a certain temperature range: too cold, and the air pressure inside isn't enough to make it bounce. Hot enough for internal air pressure to be significant, and it bounces better. Too hot, and the rubber starts losing its bounciness (as an exaggeration, think of an almost liquid composition to see that you'll start getting more and more inelastic collisions, because the spring constant starts going down a lot).
If you look at just the spring constant, though, it's roughly linear with respect to temperature.
And yeah, I think we should have more info on why the football investigation failed. How many data points did you have that you couldn't find a correlation? Did you try modeling "tackling power" as a function of two variables with, say, 20 participants or so? Less than that and the signal could be drowned out by the noise.
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The tackling experiment failed because I couldn't get the tackle bag heavy enough to register a change in velocity as the person was hitting it. Basically what I needed was for the person to hit the bag, then for the bag to slow that person down, and then I would have measured the degree to which the bag slowed that person down, and then do a load of calculations that I won't list here. It seems a bit simple but it was actually a lot more complicated than that, but I'm leaving most of it out because it didn't work anyway. What happened was that the subject would hit the bag, then the bag would just move at the same speed as the person who was hitting it, with very little change. We tried to increase the mass of the bags, but the school administration wouldn't let us cut them open and put in weights. We tried tying multiple bags together to make big ones, but when we got a change in speed it was basically just a shoulder charge, because the combined bags were so big we couldn't get our arms around them.
I'm not going into too much detail because I'm supposed to be working on it right now...haha
I'll update this post later on. Thanks for the analysis above, I haven't had a chance to think it all through yet but I'll get to it
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United States24779 Posts
On November 16 2010 00:20 aev wrote:
The tackling experiment failed because I couldn't get the tackle bag heavy enough to register a change in velocity as the person was hitting it. Basically what I needed was for the person to hit the bag, then for the bag to slow that person down, and then I would have measured the degree to which the bag slowed that person down, and then do a load of calculations that I won't list here. It seems a bit simple but it was actually a lot more complicated than that, but I'm leaving most of it out because it didn't work anyway. What happened was that the subject would hit the bag, then the bag would just move at the same speed as the person who was hitting it, with very little change. We tried to increase the mass of the bags, but the school administration wouldn't let us cut them open and put in weights. We tried tying multiple bags together to make big ones, but when we got a change in speed it was basically just a shoulder charge, because the combined bags were so big we couldn't get our arms around them.
I'm not going into too much detail because I'm supposed to be working on it right now...haha
I'll update this post later on. Thanks for the analysis above, I haven't had a chance to think it all through yet but I'll get to it
If you were having the runner tackle the bag inelastically then energy was not being conserved.
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EPT
