# Homework Help: Experimental Uncertainty - uncertainty in impact position

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1. Sep 20, 2015

### DanielleG

1. The problem statement, all variables and given/known data
The diagram shows the impact of 20 projectiles launched at the same speed and angle. What is the uncertainty in the impact position? (see attached file for picture of diagram)

2. Relevant equations
No equations, my lab instructor said through an email that I can get it "just by looking at the dots".

3. The attempt at a solution
At first I tried to find the slope of the line of best fit, but that wasn't the answer. I am just completely lost of what I am supposed to do. I know I can find it just by looking at the diagram, and it's frustrating because I know the problem is simple. I am just not sure what I'm looking for. Anyone have any ideas?

#### Attached Files:

• ###### WIN_20150920_12_24_59_Pro.jpg
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2. Sep 20, 2015

### Staff: Mentor

What is the rough spread of the dots?

Alternatively: if you shoot again, what would be a typical deviation from the central position? 1 millimeter? 1 meter? Something else?

You are probably not supposed to find a very precise answer.

3. Sep 20, 2015

### Staff: Mentor

Did he (or your other course materials) say anything at all, at any time, about what "uncertainty" means for him in a situation like this?

I'm going to go out on a limb and say what it means for me, but you should be aware that your instructor may do things differently.

Call the uncertainty Δx. When I say, "the impact position is x ± Δx", that means x is the average position, and about 2/3 of the impact positions are in the range between x - Δx and x + Δx. Based on this, what is your "eyeball estimate" of x and Δx?

If you find out something more specific from your instructor or your course materials, you can adjust accordingly.