Science Buddies: "Ask an Expert"

hello, Im a college student who is helping one of the 5th graders at our local elementary perform a science experiment. I posted this year because I figured it would get answered alot sooner. Our project is on motion parallax's.

We got the science project from science buddies.
https://www.sciencebuddies.org/science- ... ml#summary

We are having trouble getting our calculations to work out and are not sure why.
From the graph in the link I posted, our measurements are as follows:
b=1m on each side
b' for object 1=0.009595
b' for object 2=0.0107
Object 1's distance(d') from the easel is 1m, while object 2's distance(d') is 2m.
The length from the telescope to the easle is 100m.

The equation posted in the instructions is d'/b'=d/b, and we are solving for d.

We keep getting way to small a number right now. Any help would be appreciated.

This is a fun problem and good reason to get outside and get some fresh air!

I think your problem is in your original data. I see from the description of the experiment this takes some careful placement of the easel, the objects and the telescope to obtain accurate results. And it requires everything to be set up with fairly good precision at right angles.

Going through the calculations in reverse, I see the values of b1' and b2' that would have been expected if your objects and telescope were place where you intended them to be would have been 0.0101 and 0.0204 meters respectively. These are close to, but not close enough to the measurements you obtained. I can see that making the measurements of b' could be pretty tricky. One person looking through the telescope has to carefully read the grid and determine the apparent offset of the objects. With these expected measurements, the grid would have to be smaller than 1 cm to get reasonable accuracy. Perhaps this is the source of your error - too large a grid? Even if you used 1/4" x 1/4" grid paper, the error would be fairly high.

Consider the accuracy of your data and see if this explains your problem.

In the mean time, continue to engage with the younger set and help them have FUN WITH SCIENCE!

WestElementary,

I took interest in perhaps performing this experiment with my own telescope and did some sensitivity calculations to get an idea of the accuracy required. Adding onto the comment above, Ed is exactly right. To put it in perspective and highlight his comments:

Using your test set up as outlined in your post: A 0.001m (1mm) error for bprime results in ~9m of error in d1 and ~ 4.5m error in d2. So using 1/4" by 1/4" graph paper could result in errors for bprime approaching +/- 6.35mm, which would cause a very large delta in calculations for d (upwards of 50 to 60 meters) . Additionally, an error of just 0.01m (1cm) placement of your telescope from centerline (b) results in an error of ~1m for d1 (about 0.5m for d2).

Bottom line, an aggregate of small errors in one or all the measurements (b, bprime, and dprime) can significantly skew your calculations for d.