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