Why Doesn't My Impulse-Change in Momentum Lab Show a Linear Relationship?

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Homework Help Overview

The discussion revolves around an impulse-change in momentum lab experiment where the original poster presents data that does not appear to show a linear relationship as expected. The subject area is primarily physics, focusing on the concepts of impulse and momentum.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to analyze their data by calculating change in momentum and comparing it to impulse, but finds discrepancies in the expected linear relationship. Some participants question the experimental setup and data collection methods, while others suggest potential sources of error related to timing and measurement.

Discussion Status

Participants are actively exploring the reasons behind the unexpected results. Some have provided suggestions for further investigation, such as fitting the data to a line that passes through the origin, but there is no explicit consensus on the cause of the discrepancies.

Contextual Notes

There are indications of possible errors in the timing of velocity measurements relative to impulse calculations, and the original poster's data appears to be scattered, which may affect the linearity of the relationship.

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Homework Statement


Im doing an impulse-change in momentum lab, and somethings not adding up. My data is as follows:

Trial Vmin Vmax Mass Impulse
1 -.6447 .5766 .548 .9952
2 -.9044 .7803 .598 2.281
3 -.9416 .8343 .548 1.597
4 -.5553 .4425 .598 1.246
5 -1.054 .9313 .498 .9239
6 -.4706 .3409 .498 .3408

Then I figured Momentum by multiplying each Vmin and Vmax by its respective mass, then found the change in momentum by subtracting each Pmin from its respective Pmax. So the final data table looks like this:

Trial Change in Momentum Impulse
1 .6692 .9952
2 1.0074 2.281
3 .9732 1.597
4 .5966 1.246
5 .9886 .9239
6 .4041 .3408

The lab handout tells me that there should be some sort of linear relationship here, but when I graph it there's no rhyme or reason, let alone anything linear. Anyone know what I've done wrong?

Homework Equations


none, really, except that Momentum=m*v
Impulse was found with the computer program that we collected the data with

The Attempt at a Solution


its up there in part one, kind of integrated with everything else. sorry about the lack of organization
 
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Allright, I ran a best-fit line anyway and got a slope of 1.9 and a y intercept of -.23

The slope is supposed to be 1 and the y-int is supposed to be 0, since impulse=change in momentum. I would understand if there were a small error, but 1.9 is way off.

I switched axises (axes?) and got a slope of .277 and a y-int of .432.

Any ideas?
 
It would help if you told us what you did in the experiment. What was moving? What are the min and max velocities in your table? What produced the impulse and how was it measured?
 
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OlderDan said:
It would help if you told us what you did in the experiment. What was moving? What are the min and max velocities in your table? What produced the impulse and how was it measured?

Sorry, it was a cart and track setup.


|force sensor|--elastic-cord-----o|cart|o <[motion detector]

We used a Vernier LabPro, and we found Impulse with the computer by finding the area under the curve on the graph.

we pushed the cart away from the force sensor and it rebounded.
 
is my data just really off, or is there some calculation problem that I'm making?
 
Animal said:
is my data just really off, or is there some calculation problem that I'm making?

So vmin and vmax are velocities before and after the elastic has turned the cart, and hopefully the times at which those data were recorded correspond to the ends of the interval you used to calculate the impulse. I don't know how you matched up the times of velocity measurement with your force curves, but that is a potential source of error. You appear to have computed your momentum changes correctly, so I guess your data is very scattered. Fitting the curve to a line is the bast you can do.

It would be appropriate in this case to do a fit that forces the line through the origin, since you expect zero change in momentum to correspond to zero impulse. I'm not sure if your calculator or computer program gives you that option, but if your fitted curve is far from the origin and you have the option to force it to the origin you probably want to use it.