I am not sure the source of error of simple pendulum experiment

[betel]

Well, the counting part will not improve accuracy here that much. Much more important for the time accuracy is measuring 20 cycles, which will greatly reduce the error.
Well, the ruler seems so far the best possible answer. There could still be others.

 

[Raul Lai]

but it is impossible, as other group did the result of slope is 4.0875
it similar to me. beside, the error is too large

 

[betel]

Did you do the experiment or did somebody just give you the data?
When you fit a linear interpolation to your data you always need two parameters: slope and intersect. You will always get errors on both of them. But in this case, for your data, the statistical error cannot account for your wrong intersect. The intersect will be nonzero with 99.7% confidence.
So you need some explanation for it.

 

[Raul Lai]

the experiment I did is by my own hands
but, it is fine. I give up now. I should change the data to fit it
Thx for your help, it wasted you so much time
anyway, thank you.

 

[betel]

Never change data to fit theory! That is the way to hell for a physicist.
If measure something different you have to stand to your results. Propose possible error sources and possible solutions.
But never ever cheat on your data!

 

[Raul Lai]

hay~I got it. I know what wrong I did. Actually, my result is very accurate.
thank you very much. I think my report is the best in my class. I have make a silly mistake a whole day! thanks for your support. I can make a good dream now. The y-intercept is 0.0944 not 1.3. sorry to let you worry.

 

[betel]

Told you before you were a bit too large. But still you should mention explanations why you are not zero. Your other data is so good that statistics strongly (99,7%) favours a non zero result.

 

[betel]

And good night.

 

[Raul Lai]

you have a nice day too,I hope I am not a stupid and trouble guy in your mind. Can I make a friend with you?

 

[betel]

Sure. I always like to help.