# Homework Help: Figuring out relationships with graphs

1. May 18, 2006

### oooo

Ok, so as part of a lab, I had to make an excel graph of the relationship between skid distance and cone length (if you want to know more, look at my post below about science fair which was posted yesterday at 6:25 pm). Anyways, I made the graph and I can't tell the relationship between the two variables. I am just a freshman with little math behind me, so I can't quite determine the relationship just by looking at it. Please give me soem tips on determining the relationship as shown on my graph. (I tried to attach it, but the site said it was invalid, so I can't)
Thanks!

Last edited: May 18, 2006
2. May 18, 2006

### Hootenanny

Staff Emeritus
Could you describe it? Or perhaps you could sopy it into an image editing program and attached it as an image?

~H

3. May 18, 2006

### oooo

ok, I uploaded it...can we just say it is an inverse relationship?

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• ###### graph.bmp
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Last edited: May 18, 2006
4. May 18, 2006

### Hootenanny

Staff Emeritus
Well, I'll let you start. Does skid distance increase or decrease with increasing cone length?

~H

5. May 18, 2006

### oooo

it decreases in this portion of the graph

6. May 18, 2006

### oooo

so wouldn't it just be an inverse relationship because as cone length increases, skid distance decreases?

7. May 18, 2006

### Hootenanny

Staff Emeritus
Almost but the curve isn't a straight line is it? What kind of curve does it look like?

~H

8. May 18, 2006

### oooo

its exponential. what does that mean about skid distance and cone length?
I knew it didn't look like an inverse function, but in theory shouldn't it have been?

9. May 18, 2006

### Hootenanny

Staff Emeritus
Yeah, there aren't enough data points to confirm, it could either be an inverse square relationship or an exponential decay. I'm gona go and have a look at your other thread now to see what you were actually invesitgating.

~H

10. May 18, 2006

### oooo

ok, i appreciate it

11. May 18, 2006

### Hootenanny

Staff Emeritus
From what you have said and the diagram you have supplied, I would have expected that cone length to be independant of skid length. I would therefore have expected to obtain a horizontal line. Interesting...hmmm

~H

12. May 18, 2006

### oooo

my data:

10 cm cone: skid distance= 38.9 cm
15 cm cone: skid distance= 22 cm
20 cm cone: s.d.= 12.5 cm
25 cm cone: s.d.= 10 cm
30 cm cone: s.d. = 9.2 cm

Now, I know that friction is independent of surface area because the reduction of pressure with increased skid distance offsets the increase in friction. But, each cone does have a different mass, and so does the decreasing pressure not completely offset the friction between these trials?

13. May 18, 2006

### Hootenanny

Staff Emeritus
Ahh, I forgot you are taking mass into account. Yes, this may explain it, however, the decrease seem rather rapid. Have you calculated the changes in kinetic friction with respect to mass?

~H

14. May 18, 2006

### oooo

these cones are made of paper, so is the difference between the masses of the cones negligible?

15. May 18, 2006

### Hootenanny

Staff Emeritus
That's what I was thinking when I said the decrease seems rather rapid. I think its best to wait and see if anyone else has any ideas, cos I'm fresh out

~H

16. May 18, 2006

### oooo

ok, thanks so much for all your help!