How stretching a rubber band, affects the range of a shot?

[rasalzari]

Homework Statement

I did an experiment on how stretching a rubber band, affects the range or distance of a projectile shot.
Variable list:

• Independent Variable
  • Amount of stretching
• Dependent Variable
  • Range or distance

I created my catapults on my own and used two different rubbers bands and compared them

2. The attempt at a solution
Then I calculated the average, however i wanted to show that there is a linear relationship between the stretch and the range, but i don't know much about it. so can you help in determining whether what i did was right or wrong?

Then I graphed the average and produced a line of regression, but it didnt pass through the points so its not linear... Also i wondering whether i can get the potential energy, is it possible?

 

[kuruman]

hen I graphed the average and produced a line of regression, but it didnt pass through the points so its not linear...

That's not necessarily true. You need error bars. Your line may not pass through the average, but does it pass through any of the measured values? Can you estimate what they are? If not, plot all three points instead of the average and see what you get. Also, the angle of launch is critical for the range. What did you do to make sure that the angle was the same in all launches?

Also, your plot is unconventional. The independent variable is on the horizontal axis and the dependent variable on the vertical, not the other way around. For a linear plot it doesn't make much difference, but for other kinds of dependence it could be confusing and disorienting to the viewer.

 

[rasalzari]

That's not necessarily true. You need error bars. Your line may not pass through the average, but does it pass through any of the measured values? Can you estimate what they are? If not, plot all three points instead of the average and see what you get. Also, the angle of launch is critical for the range. What did you do to make sure that the angle was the same in all launches?

Also, your plot is unconventional. The independent variable is on the horizontal axis and the dependent variable on the vertical, not the other way around. For a linear plot it doesn't make much difference, but for other kinds of dependence, it could be confusing and disorienting to the viewer.

Alright, i will try inputting all the measurements and see what happens, however, i did add the error bars but for some reason, it's only visible when u zoom in. I used ploty https://plot.ly/create/ to get the line of reg.

 

[rasalzari]

That's not necessarily true. You need error bars. Your line may not pass through the average, but does it pass through any of the measured values? Can you estimate what they are? If not, plot all three points instead of the average and see what you get.

I tried all measurements, it is still not linear. :(

What did you do to make sure that the angle was the same in all launches?

I think i might have done it wrong :|

 

[rasalzari]

That's not necessarily true. You need error bars. Your line may not pass through the average, but does it pass through any of the measured values? Can you estimate what they are? If not, plot all three points instead of the average and see what you get. Also, the angle of launch is critical for the range. What did you do to make sure that the angle was the same in all launches?

Also, your plot is unconventional. The independent variable is on the horizontal axis and the dependent variable on the vertical, not the other way around. For a linear plot it doesn't make much difference, but for other kinds of dependence it could be confusing and disorienting to the viewer.

is it alright if the best line of fit misses the one point? will it considered linear?

 

[kuruman]

is it alright if the best line of fit misses the one point? will it considered linear?

Yes and no. Let me explain. You need to understand how well your theory of linearity matches the experiment that you undertook. "Linear" in your case means that the range is proportional to the stretch for all values of the stretch. So answer me this, why did you start stretching at 0.10 m? What if you started at 0.01 m or 0.001 m?

 

[mfb]

Why do you expect a linear relation?

Also i wondering whether i can get the potential energy, is it possible?

If you know the launch angle and the projectile mass, you can make some estimate about the kinetic energy of the projectile.

however, i did add the error bars but for some reason, it's only visible when u zoom in.

Error bars should be based on the variations between the trials, not based on the measurement uncertainty of the individual launches. Your estimate for the average is much more uncertain than a millimeter.If your measurement uncertainty is really a single millimeter as shown in the table (I doubt that), you should give the measured ranges with one more digit.

 

[rasalzari]

Why do you expect a linear relation?If you know the launch angle and the projectile mass, you can make some estimate about the kinetic energy of the projectile.
Error bars should be based on the variations between the trials, not based on the measurement uncertainty of the individual launches. Your estimate for the average is much more uncertain than a millimeter.If your measurement uncertainty is really a single millimeter as shown in the table (I doubt that), you should give the measured ranges with one more digit.

fixed it, thank you for replying

Yes and no. Let me explain. You need to understand how well your theory of linearity matches the experiment that you undertook. "Linear" in your case means that the range is proportional to the stretch for all values of the stretch. So answer me this, why did you start stretching at 0.10 m? What if you started at 0.01 m or 0.001 m?

oh good point, ill try doing it and thank so much!