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Topic: Determining accleration due to gravity (Read 11 times) previous topic - next topic

wwbrown

There are far easier ways to measure the acceleration due to gravity using Arduino.  You can buy a photointerrupter like http://www.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&keywords=425-1935-5-ND&x=0&y=0&cur=USD, build the simple circuit shown in the data sheet.  Then get a piece of plexiglas maybe 2" x 10" and use electrical tape to make uniformly spaced opaque strips that are perpendicular to the long axis.  Take the signal from the photointerrupter and input that into one of the interrupt pins for timing purposes.

Dropping the plexiglass strip through photointerrupter, lets call it a photogate, from the times displayed by the Arduino on the computer screen or LCD you can determine the acceleration due to gravity.

You may find that the plexiglass hits the photogate and this will increase the uncertainty of the measurement and you can either accept that or break the photogate and mount the two pieces on another frame to make a larger fixture so the plexiglass will hit it less often.

I have left out some steps as there is a derivation needed utilizing some kinematics to be worked out but it is not too bad. 

AWOL

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There are far easier ways to measure the acceleration due to gravity using Arduino

How is that "far easier" than using an accelerometer?
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

liudr


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There are far easier ways to measure the acceleration due to gravity using Arduino

How is that "far easier" than using an accelerometer?

I share the same doubt with AWOL. If you really want an easy method, define what equipment you have first. The easiest one that requires no electronics would be using your own pulse as a time reference as Galileo probably did in his time, or use your watch/clock. Then hang a pendulum (any heavy and compact object will do, such as a key or a stack of coins taped together) with a known string length L. Watch it oscillate say 100 periods and solve the simple T=2*PI*sqrt(L/g) equation to get g. The period should be fairly close to 2 seconds for 1m string. For those in the US, I know for sure you will have 5,6,7 foot references (relatively accurate) right outside most bank branches. You don't even have to own a tape measure.

AWOL

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with a known string length L

A pendulum should be rigid.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

MarkT


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with a known string length L

A pendulum should be rigid.

a) Why?  A swinging chain keeps time.
b) A string under tension _is_ rigid.
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