Verifying the acceleration of gravity in our lab (help with error please)

[feynmansorange]

Homework Statement

Hi! I'm doing a lab where my class is verifying the acceleration due to gravity. We dropped an object and recorded the time with a spark timer, then measured the meters every 1/30th of a second. So, I have distance (meters) and time (seconds). THEN we square the time, and plot that on a graph of dist. vs time^2. But my slope is only roughly half of gravity??? isn't the acceleration supposed to be equal to gravity?

Relevant Equations

s=ut+1/2at^2

Data and graphs here (the time is measured every 1/30 of a second, but for some reason, Google Sheets thought 1/30 wasn't a number so its in decimals!!! very confusing!!! so sorry about that!). why is the slope only 4.68, should it not be 9.81m/s^2? is the slope of m/s^2 not supposed to be acceleration due to gravity? is my data weird? thanks!

 

[Tomy World]

In your experiment, s = (1/2)g t²

After your conversion and plot, your graph is similar to following equation.
y = (1/2)g x .... general equation of a straight line.
Slope is therefore (1/2)g, .... there's nothing wrong, right?

 

[kuruman]

In your experiment, s = (1/2)a t

You mean s = (1/2)a t². Then x = t² in the straight line plot.

 

[Tomy World]

You mean s = (1/2)a t². Then x = t² in the straight line plot.

YEs. When you plot s vs t², it becomes a straight line equation.

 

[kuruman]

Homework Statement: Hi! I'm doing a lab where my class is verifying the acceleration due to gravity. We dropped an object and recorded the time with a spark timer, then measured the meters every 1/30th of a second. So, I have distance (meters) and time (seconds). THEN we square the time, and plot that on a graph of dist. vs time^2. But my slope is only roughly half of gravity??? isn't the acceleration supposed to be equal to gravity?
Relevant Equations: s=ut+1/2at^2

Data and graphs here (the time is measured every 1/30 of a second, but for some reason, Google Sheets thought 1/30 wasn't a number so its in decimals!!! very confusing!!! so sorry about that!). why is the slope only 4.68, should it not be 9.81m/s^2? is the slope of m/s^2 not supposed to be acceleration due to gravity? is my data weird? thanks!

Now that your question abut the slope has been answered, how do you explain the intercept of about -6 cm? You need to address that question in your report and it seems that you already have the necessary information to do just that.

 

[feynmansorange]

Now that your question abut the slope has been answered, how do you explain the intercept of about -6 cm? You need to address that question in your report and it seems that you already have the necessary information to do just that.

yeah, I also noticed that the intercept was off and makes no sense. My physics teacher (who has 0 background in physics because the previous teacher quit a few days before school started) made us measure it like that. I really wish I had an actual teacher.

 

[kuruman]

yeah, I also noticed that the intercept was off and makes no sense. My physics teacher (who has 0 background in physics because the previous teacher quit a few days before school started) made us measure it like that. I really wish I had an actual teacher.

Please don't blame your teacher. You can figure this out on your own because it's your doing. Look at your data. No intercept means that at t = 0 the object is at distance = 0. Your table shows that distance = 0 at time t = (1/30) s.

 

[Tom.G]

Hi @feynmansorange,


A clue to the source of plot problem:
Note that the plot shows minor variations from a straight line at times
0, 0.3, 0.55. That repetition at similar intervals make me suspicious that the either the Time or Distance measurements (or both) may have a systematic error.

Don't expect your test setup or equipment is always perfect. I think @kuruman is hinting at that possibility.

Cheers,
Tom
p.s. It would be interesting to see if others in the class had similar results.
Please let us know if you find out.