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# Physics/gravimeter

Question
QUESTION: Is there a way to build a gravimeter for less than \$100? Maybe 1 or 2 decimal places less accurate than the high end ones?

ANSWER: Interesting challenge.  The thing is that a gravimeter has to be really sensitive to be useful.  If you just want one or two decimal places of accuracy, you can generally find that with simple experiments involving falling masses and a timer.  What makes a gravimeter so expensive is the face that it measures the difference in gravity between two points.  How far do you intend to move it to make it read differently, up a mountain or something?  I'm not sure where your "one or two decimal places" are, in the absolute reading or the difference between two places.

---------- FOLLOW-UP ----------

QUESTION: I was just wondering if gravity fluctuates much in one place? I was trying to imagine how I could use a natural fluctuation in nature to produce data to create art work somehow.

Gravity is generally very constant in one place and does not fluctuate.  As you move around closer to and further from dense objects and move up and down it varies, but very little.  If you go up an inch (gravimeters are sensitive on that scale), using your basic formula for the gravitation and the Earth's radius, the force of gravity only goes down by a little less than a part in a billion.  So you really need nine decimal places of accuracy to measure such a change.  That's why those instruments are so expensive, they're extraordinarily precise.

Physics

Volunteer

#### Dr. Stephen O. Nelson

##### Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

##### Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.