Lab Report Physics IA graph

[flyingturducken]

 Hi all,

 

I'm having some difficulties over the maximum/minimum trend lines for my graph. Here is the original one with the line of best fit added: 

And this is after I added the maximum/minimum lines: 

 

Now the problem comes in the minimum line, because it goes above the original trend line. The only way I can solve this is if I discount the upper and lowermost point, but they're not really anomalous as the final calculations graph looks like this:

 

If it helps, this IA is about circular motion: the first 2 charts are for the relationship between radius(y) and period(x), and the last chart shows the relationship between centripetal force(y) and velocity(x). 

 

Thanks in advance. 

Edited December 23, 2015 by flyingturducken

[Vioh]

Hi all,

I'm having some difficulties over the maximum/minimum trend lines for my graph. Here is the original one with the line of best fit added: 

And this is after I added the maximum/minimum lines: 

Now the problem comes in the minimum line, because it goes above the original trend line. The only way I can solve this is if I discount the upper and lowermost point, but they're not really anomalous as the final calculations graph looks like this:

If it helps, this IA is about circular motion: the first 2 charts are for the relationship between radius(y) and period(x), and the last chart shows the relationship between centripetal force(y) and velocity(x). 

Thanks in advance. 

 

In order to help you, I think I need more information about your research. How did you carry out the experiment? Which variables did you do the measurements on? Are the first 2 graphs your raw data? What type of circular motion did you study? Is it uniform circular motion? because if it is, there should be some kind of uniformity in your graph, but your first graph seems like a complete chaos to me. Also what do you mean by radius vs period? Which one is in the x-axis and which one is in the y-axis? What did you do to transform the first graph into the third graph? Lots of questions, I know. But I'm not really clear about what you did. Right now, I can only speculate 3 things. Either:

• some of the points on your first graph are anomalies, or
• your max & min lines are wrong because they are supposed to also tackle the fact that your data are spread far away from the trend-line, or
• you're not supposed to draw the trend line in the first place because there's no relationship between the radius and period in your experiment

[flyingturducken]

Yeah, it's about uniform circular motion. I don't know what's going on the first graph, because like you said I was anticipating it to be more ordered. I did try fixing the second one however to show Fc over v^2, which is significantly more linear than the rest. I was hypothesising that maybe the radius had a relationship with the period as the bung was spinning at the specific speed with the radius I recorded (a hollow glass rod was slid over the string to act as the handle so the bung pulls up the weights at the other end to produce a radius). The experimental method was really uncontrolled (I was spinning a bung tied to a string manually), so I guess all this mayhem can be chalked up to inconsistency in the evaluation

Though I'm still curious of what to do in the case that another graph with more precise data shows that same inconsistency as the first chart. Am I still supposed to measure the slopes from the first and last points even though they don't appear to be in the right place relative to the actual trend line?

[Vioh]

Yeah, it's about uniform circular motion. I don't know what's going on the first graph, because like you said I was anticipating it to be more ordered. I did try fixing the second one however to show Fc over v^2, which is significantly more linear than the rest. I was hypothesising that maybe the radius had a relationship with the period as the bung was spinning at the specific speed with the radius I recorded (a hollow glass rod was slid over the string to act as the handle so the bung pulls up the weights at the other end to produce a radius). The experimental method was really uncontrolled (I was spinning a bung tied to a string manually), so I guess all this mayhem can be chalked up to inconsistency in the evaluation

Though I'm still curious of what to do in the case that another graph with more precise data shows that same inconsistency as the first chart. Am I still supposed to measure the slopes from the first and last points even though they don't appear to be in the right place relative to the actual trend line?

 

I'm still very confused about the procedure of your experiment. The last graph shows the relationship between Fc and v^2. Well, theoretically,

 

, where 'm' is the mass of the bung (with the weights), and 'R' is radius.

 

Since 'm' is constant and the last graph shows a linear relationship between Fc and v^2, this means that the radius R stays essentially constant throughout your entire experiment. But then how did you create the first graph in the first place? because you didn't even change the radius???

 

You also said that you hypothesized some form of linear relationship between radius and period. Well, theoretically, for the 2 variables to have the linear relationship, then

 

where is the angular frequency/speed.

 

This means that the speed 'v' has to stay essentially constant in your experiment in order to achieve a linear relationship between the two variables. But then how did you plot the last graph in the first place? because the last graph (F_c against v^2) suggests that you changed the velocity/speed of the bung?

 

Generally, I find the first and the final graph to be inconsistent with each other, and with the confusing info that you've given me, I don't really know how to help you at all. Can you be a little more precise on how you carried out your experiment? What do you mean by you spinning the bung manually? like using your wrists? In that case, how did you even record the centripetal force and other data? What experimental equipment did you use? And most importantly, how did you make all the graphs that you posted from the raw data that you had recorded?

btw, what exactly is the purpose of your experiment?

Edited December 23, 2015 by Vioh

[flyingturducken]

Sorry for the confusion. The experiment had been prescribed to our class, and its purpose is to show the relationship between centripetal force and uniform velocity at a horizontal circular motion. What it detailed was we were to have a 1m length of string, with masses (kept the same throughout) tied to one end (with a mass hanger) and a bung in the other. The string had been slid in to a hollow glass rod, which we used as the handle. We then proceeded on to spin the bung end of the string using the glass rod with our wrists, so the radii velocities varied with each trial; the only variable we maintained was the time, which we measured using a stopwatch until 20 seconds. A paper clip had been tied onto the string supposedly to keep the radius constant, but it kept sliding into the glass rod so it wasn't really helpful at all. In the end, we recorded the radius of string using a metre rule by holding onto it with the other hand while the contraption keeps spinning.

 

Theoretically the relationship should be that v² and F_c should be m/r. Substituting the variables onto the trend line equation (y=0.152x+5.451), it kind of doesn't make sense... which I guess is because m was constant and r varied. 

[Vioh]

Sorry for the confusion. The experiment had been prescribed to our class, and its purpose is to show the relationship between centripetal force and uniform velocity at a horizontal circular motion. What it detailed was we were to have a 1m length of string, with masses (kept the same throughout) tied to one end (with a mass hanger) and a bung in the other. The string had been slid in to a hollow glass rod, which we used as the handle. We then proceeded on to spin the bung end of the string using the glass rod with our wrists, so the radii velocities varied with each trial; the only variable we maintained was the time, which we measured using a stopwatch until 20 seconds. A paper clip had been tied onto the string supposedly to keep the radius constant, but it kept sliding into the glass rod so it wasn't really helpful at all. In the end, we recorded the radius of string using a metre rule by holding onto it with the other hand while the contraption keeps spinning.

 

Theoretically the relationship should be that v² and F_c should be m/r. Substituting the variables onto the trend line equation (y=0.152x+5.451), it kind of doesn't make sense... which I guess is because m was constant and r varied. 

 

uhm, I guess the experiment that you did was kinda similar to the instruction here: http://www.geocities.ws/hkheman/TAS/Expt/centripetalforce.doc

 

Anyway, correct me if I'm wrong, but weren't you supposed to keep the Radius R constant at all times??? I mean the purpose of the experiment is to demonstrate that there is a relationship between and . So theoretically, you are trying to prove that this equation holds:

This means that you must change F_c as an independent variable (by increasing the mass attached to the end of the string), while spinning the bung in such a way that the radius R is fixed at all times in order to prove that there is a linear relationship between F_c and v². That is also the reason why you've tied a paper clip onto the string; to keep the radius constant!!!, exactly like you said above.

 

Now, if you were to do an experiment to demonstrate the relationship between the radius R and the period T, then you would be allowed vary the radius. But in this case, you will have to keep the mass fixed at all times in order to keep the F_c constant. So for this experiment, all you need to do is to increase the speed at which you spin the bung after each trial in order to change the period as an independent variable, and then you can see how the radius changes as you change the period. However, since this is not the purpose of your experiment, you cannot change the radius!!!

 

Your problem here is that you have created 2 different graphs (graph 1, and graph 3) for two completely different experiments with completely different purposes. The first graph is supposed to be for an experiment determining relationship between radius and period, in which you're supposed to keep the force (i.e. the mass) constant. On the other hand, the third graph is supposed to be for an experiment determining relationship between force and the uniform speed, in which you're supposed to keep the radius constant. Therefore, it's contradictory if you plot both of the graphs for your experiment. So unless I'm wrong about all the things I've written here, my suggestion to you is to forget entirely about the first graph (and eventually the second graph), and only include the third graph into your lab report. This is because the third graph shows a pretty good linear relationship, while still fulfilling the purpose of your experiment that you've stated in your previous post. You can just pretend that you did try to keep the radius constant as a controlled variable. But mention in the evaluation that the radius occasionally changes a little bit because you saw the paper clip sliding into the rod several times.....

Hope this is clear for you!

Edited December 24, 2015 by Vioh

[flyingturducken]

Yeah the experiment got really messed up. Thanks for the advice