Measuring distance of rotating object

  • Thread starter Thread starter Chynkinese
  • Start date Start date
  • Tags Tags
    Measuring Rotating
Click For Summary

Discussion Overview

The discussion revolves around measuring the distance from a stationary point to a moving object that is rotating uniformly in a circle at an angle to the horizontal plane. The participants explore various methods and considerations for achieving accurate measurements, particularly in the context of a rotating system with potential elongation of the string used to connect the object.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes a method using a ruler with a pointer to measure the distance, noting potential inaccuracies of +/- 1cm to 2cm.
  • Another participant questions whether the distance is measured from the axis of rotation or an arbitrary point and asks about the required data refresh rate.
  • A participant clarifies that the measurement is from the axis of rotation and mentions the use of a motor from a power drill for steady rotation.
  • One participant suggests that if measuring from the axis, the distance to the object could simply be the length of the string, but another points out that the string elongates during rotation, complicating the measurement.
  • One idea proposed involves projecting the shadow of the moving object onto a white background to measure the distance to the pivot.
  • Another participant mentions that a hand calculation based on rotating velocity and mass could yield results comparable to physical measurements, suggesting a method to find elongation through stress and strain calculations.
  • Concerns are raised about the difficulty of determining Young's Modulus for the strings being used, which is necessary for stress-strain calculations.
  • A later reply proposes an experimental approach to determine Young's Modulus by hanging a weight from the string and measuring deflection.

Areas of Agreement / Disagreement

Participants express a range of ideas and methods for measuring the distance, with no consensus on a single approach. There are competing views on the accuracy of different measurement techniques and the implications of string elongation.

Contextual Notes

Participants note limitations related to the accuracy of measurements, the need for specific equipment, and the challenges in determining material properties like Young's Modulus for the strings used.

Chynkinese
Messages
4
Reaction score
0
Please ignore the periods in the diagram as it won't allow me to properly draw it otherwise.

I have an object, attached to a string, rotating uniformly in a circle but at an angle to the horizontal plane. It is going at 80RPM (so relatively slow). How would one go about measuring the length from stationary point o to moving object a? the length can range anywhere from 40cm to 70cm and the accuracy for the measurement should IDEALLY +/- 0.5cm (doesn't mean it has to since real life is never ideal).

ie......o
....../
....../
....../
...../
...a

Nothing can be attached to "a" unless it is extremely light (such as reflective tape for a laser or something).

I have a very simple idea but the accuracy is easily +/- 1cm to 2cm or so. It's a simply ruler with a pointer attached and I slide it as close as possible. And I do the same for the vertical (either that or I measure the angle, whichever is more accurate). It goes something like this:

ie...___Ruler___o
...|.../
...|.../
...|.../
...V./
...a

I thought about using a laser somehow but I can't seem to find any equipment suitable for this.
 
Engineering news on Phys.org
Is the distance your measuring from the axis of rotation or arbitrary? How quickly do you need the data (refresh rate)?

Is the rotation steady?

What type of equipment do you have at your disposal?
 
I'm measuring from the axis of rotation (axis goes vertically through point "o").

Rotation is assumed to be steady; it is done by the motor taken from power drill and fed by a lab DC power supply which is kept at a constant amperage and voltage.

I have access to me equipment that is usually available in a well equipped lab. As well, I am free to order any other necessary parts. Granted, I'm not ordering thousands of dollars worth just to test a theory.
 
Last edited:
Well, if you're measuring from the axis of rotation, then isn't the distance to the object simply the distance of the string that you used to connect it?
 
The problem is the string elongates during rotation and we need to know by how much.
 
Can you project the shadow of the moving object onto a white background. Mark the location and measure the distance to the piviot with a ruler. The light would need to be in the plane of the rotating object.
 
If the rotation is steady, then a hand calculation would probably get you just as close as any measurement. Take your rotating velocity and mass and find the tension that is generated in the string. Find the stress->strain and then elongation.
 
Can you project the shadow of the moving object onto a white background. Mark the location and measure the distance to the piviot with a ruler. The light would need to be in the plane of the rotating object.

That's an idea...I could give that a try but I don't know how accurate it'd be.

If the rotation is steady, then a hand calculation would probably get you just as close as any measurement. Take your rotating velocity and mass and find the tension that is generated in the string. Find the stress->strain and then elongation.

I thought about that. But the stress->strain requires Youngs Modulus does it not? I don't think it'd be possible to find the modulus for the strings I'll be using. :S
 
Chynkinese said:
I thought about that. But the stress->strain requires Youngs Modulus does it not? I don't think it'd be possible to find the modulus for the strings I'll be using. :S

Then do an experiment. Hang a weight from the string and measure the deflection. Boom, Young's modulus (or at least a very good number for you to use).
 

Similar threads

Translating reciprocating motion into a 45 degree rotation
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad Spacetime distance and ruler-measured length on an XT chart
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Are all processes CPT symmetric like measurement, stimulated emission?
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad Is it feasible to measure one way speed of light this way?
  • · Replies 52 ·
2
Replies
52
Views
6K
Graduate Ideas for determining the volume of a rotating object
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad Set of possible rotations of a 3D object and the rotation history
  • · Replies 40 ·
2
Replies
40
Views
9K
How can I rotate Euler angles through a specific angle?
  • · Replies 1 ·
Replies
1
Views
3K
Graduate Distance between fast moving objects
  • · Replies 26 ·
Replies
26
Views
6K
Distance Measuring Sensor Advice
  • · Replies 4 ·
Replies
4
Views
2K
Circular Motion — Object on a rotating conic surface....
  • · Replies 20 ·
Replies
20
Views
5K