Rolling ball down ramp to calculate acceleration of gravity

Reply Sat 26 Dec, 2015 10:34 pm
Well put, PP.

Premises can be adopted because they are directly perceived to be necessary truths (or because they are believed to be or assumed to be such). They can also be adopted as provisional or working premises. And finally, they can be entirely arbitrary....the need to base logical arguments and proofs on stipulated premises cannot be escaped.

This is something that a lot of people with scientific training seem to forget. They think that science "proves" things. Neither logic nor the so-called "scientific method" can prove anything. You can only know that certain conclusions or outcomes are (or are not) consistent with your premises.

I have engaged with Max and many others here on the topic of special relativity vs alternate theories of relative motion. It is very hard to come across someone who actually understands the relationship between premises and conclusions in that setting. They seem to assume that whatever premises there are, the have been "experimentally proven" and are hence indubitable. They seem to think, therefore, that it is a waste of time to even examine the premises.
Reply Sun 27 Dec, 2015 03:40 am
I wrote something perhaps relevant to your Special Relativity objections in the"Spacetime and mass" thread:


The basic idea is that General Relativity, through the Riemannian metric tensor, assumes that all local (observer dependent) coordinate systems must be invariant, and are therefore common expressions (albeit in the "local" language) of a universal coordinate system describing absolute spacetime.
cicerone imposter
Reply Sun 27 Dec, 2015 01:06 pm
Can you translate that into English?
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Reply Sun 27 Dec, 2015 01:35 pm
there are several test questions in undergraduate geophysics (where the measurement of micro-gravity anomalies is actually a TOOL of resource exploration), to measure gravity using a 2.5 cm diameter stainless steel ball (weighing 31 grams), in an inclined track, with a laser timer.
Its a complicated but quite doable measurement technique. (hint: the balls diameter and weight are of no value)
Reply Sun 27 Dec, 2015 06:45 pm

I wasn't aware of the effect. Insofar as vertical motion goes, it's not clear to me if it's something that "can" happen or something that "invariably" happens with a bullet.

I don't think it really makes any difference with the respect to the point I was making, but, to avoid any technical disputes, I'll just retroactively add "in a vacuum" to my post on the topic. How's that?
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Reply Sun 27 Dec, 2015 07:01 pm
Is a steel ball on an inclined track really the easiest way to do this? I would think a pendulum would simpler and more accurate.

Reply Sun 27 Dec, 2015 08:10 pm
You are quite Correct. its just a problem so devised to get the kids familiarized with detail gravimeters. Using the roller ball (with lots of red herring data , like balls specifications). The kids learn that G becomes a constant that is derived using a homemade graph of (angle of repose v speed over constant distance). They can actually generate the field equations and unique gravity acceleration by understanding several equivalents and independent variables. (Gravity only varies by lkess than half a percent all over the world in all kinds of rock masses and we have standard gravity stations against which we calibrate instruments ) However, newer relative techniques can use a cell phone to give a g value as accurate as 0.0001% off your cell phone GPS)

Yeh a real gravity meter and a micro gravity meter, used to use either a QUARTZ or a calibrated metal spring accelerometer .(Many of the true specific gravimeters used by USGS and oil companies are still the clunky but very accurate spring accelerometers installed in a ( 1lb gas cylinder sized ) vacuum chamberand these are laser and computer controlled , with data going via usb into a (non ipad) tablet. Thee are accurate in the pica gal ranges

The reason we have the kids learn the overall nuts and bolts of gravitometers is because the standard relative gravity meter is nothing more than an accelerometer like that on your smart phone. (Most app stores can give you apps to turn your cell phone into anything from a cosmic ray detector , seismograph, cheap magnetometer (to a point) AND a GRAVITY METER (gravitometer). So, if the kids just take off in the field with their cell phones apped up, they really wont understand what theyre measuring . So we actually make em make some of the gizmos they will use in their later careers.
So the very smart tool that protects your cell phone from suffering a concussion when you knock it off your truck bed and it hits the fuckin rock outcrops 20 feet below, is a little geophysical instrument that some kid at Calgary sold to one of the cell phone companies years ago .(Accelerometers were in use in flip phones back in the 90's), just couldnt be used for anything
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