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 May 15th, 2017, 11:20 AM #1 Newbie   Joined: Oct 2016 From: United States of America Posts: 7 Thanks: 0 Indirect Measurement Methods What are a few unique ways to use indirect measurement in real life? Example: Using a mirror on the ground and using the shadow of an object. Thank you in advance!
 May 15th, 2017, 11:33 AM #2 Senior Member   Joined: Aug 2012 Posts: 1,852 Thanks: 511 Can you define direct versus indirect? For example if I use a Galilean telescope (straight through optics) is that direct? And a Newtonian telescope (uses a mirror) is indirect? Is it the use of a mirror that makes a measurement indirect?
 May 15th, 2017, 11:53 AM #3 Senior Member     Joined: Sep 2015 From: USA Posts: 1,860 Thanks: 967 If using a mirror constitutes an indirect measurement, then all reflector style telescopes make indirect measurements. Interferometers make time or distance measurements by zeroing out interference patterns in interacting laser beams. This probably fits your definition of indirect. Liquid thermometers measure temperature by reporting the calibrated change of the volume of a liquid due to temperature. That's probably indirect. Last edited by skipjack; May 15th, 2017 at 12:26 PM.
May 15th, 2017, 02:17 PM   #4
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Using one of these
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 May 15th, 2017, 03:18 PM #5 Newbie   Joined: Oct 2016 From: United States of America Posts: 7 Thanks: 0 Indirect: Not coming into contact with the object. For example, if you were to measure the distance from the pole a to pole b, you would have to do so without touching it in any way shape of form. Direct: Measuring with contact. For example, if you were to take a measuring tape and measure the distance from the pole a to pole b and come into contact with both of the objects, this would be direct contact.
May 15th, 2017, 04:49 PM   #6
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Quote:
 Originally Posted by Imnomermaid112 Indirect: Not coming into contact with the object. For example, if you were to measure the distance from the pole a to pole b, you would have to do so without touching it in any way shape of form. Direct: Measuring with contact. For example, if you were to take a measuring tape and measure the distance from the pole a to pole b and come into contact with both of the objects, this would be direct contact.
Question to help me understand your definition.

When I look at a light source, the photons hit my retina, an electrical signal goes up the optic nerve to my brain, and I have a subjective experience of brightness. [Whoever figures out how the subjective experience happens wins every prize there is].

My eye/brain system isn't very quantitative. It's not even very reliable. To measure the intensity of the light I have to intercept the photon stream with a photoelectric cell, and read off the current generated by the photons, which is proportional to the number of photons per unit of time.

Is that direct or indirect?

If I bounce the photons off a mirror first does that make it indirect? What is the deal with mirrors?

 May 15th, 2017, 05:08 PM #7 Senior Member   Joined: Feb 2016 From: Australia Posts: 1,579 Thanks: 541 Math Focus: Yet to find out. Hall effect sensors come to mind for the 'indirect' case.
 May 15th, 2017, 06:12 PM #8 Math Team   Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 12,130 Thanks: 801 Train an ant to walk at speed x. Have the ant walk from pole to pole. Get a timewatch. You know what I mean....

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