# Centripetal Acceleration lab question

1. Mar 11, 2009

### EBM

1. This is more of a general question about a lab report I'm doing:
The purpose of this lab is to find if the acceleration of a person sitting on the end of a steel beam is moving at a constant acceleration, if they aren’t accelerating, or if acceleration changes with time.

I have all my data, equations, and final numbers I just can't tell what the centripetal acceleration is doing. Does it stay constant? or does it change with time?

2. Relevant equations
(ὠ^2)(r) = ac

3. The attempt at a solution
Here is my prediction:
(4.2^2)(.24m) = 4.21 rad/s^2 = ac
The actual fit number I came up with is 4.85 rad/s^2 and this was the average of a chart of average accelerations found from recorded different x and y values as a platform rotated around. I just can't tell if it is constant, changing with time, or 0.

Thanks for the help.

2. Mar 11, 2009

### Delphi51

It is very difficult to tell what the problem is. Was the person in circular motion?
How did you average the x and y accelerations? How were they measured?
For circular motion, I would expect the x and y accelerations to vary sinusoidally while their combined magnitude would be constant.

3. Mar 11, 2009

### EBM

There is an amuesment park ride where people sit on the end of a rotating steel beam. For my lab we took a video of a beam rotating from its center. The camera was placed above the center facing down. After this was done it was brought into a computer program to be analyzed. We plotted points at the tip of the rotating beam as it went around. This gave us x and y and the t at which the occured for every point (35 points plotted). From this we found Vx with: dx*dt and Vy with: dy*dt. Then we found the acceleration in the x direction with:dVx/dt and in the y direction with dVy/dt. Finally an average acceleration was found with SQRT((Ax^2)+(Ay^2)). From the average acceleration we are supposed to conclude if it was constant, 0, or changing. I'm having trouble figureing out which one it is. It is all dependent on the velocity. So as the velocity changes so does the acceleration?

I'm just worried because the last time we had a lab report (motion up and down an incline) I said the accleration was changing and I lost a ton of points because it was constant.

4. Mar 11, 2009

### Delphi51

So you have values of Ax, Ay and A = SQRT((Ax^2)+(Ay^2)) at various times?
What do the numbers look like? Have you got a graph of them versus time? I'm sure the Ax and Ay will vary, but the SQRT may well be constant to within the accuracy of measurement. Can you estimate the accuracy of your measurements of x, y and t? And deduce the accuracy of Ax, Ay and A from that? Only then can you say if they are constant to within the accuracy of measurement.