[geocentrism] Re: acceleration calcs

Allen D
 
It may be that I just don't understand your descriptions -- heaven knows I am 
not alone and you do little to ameliorate this -- but I'm going to proceed on 
the basis that I do understand what you are saying. I'm not going to address 
your objections point by point -- that is a quagmire that I for one have been 
bogged down in more than once. I'm going to be charitable and assume that you 
still do not grasp what I'm saying about accelerometers.
 
An accelerometer is a mass suspended in some manner, such as by a spring, in a 
vehicle which is to be accelerated. Now if we were to hang this device from a 
stationary beam in a 1 'g' gravity field, and it has a mass of 1 kg, then the 
spring will be extended, coming to a halt when the spring exerts an upward 
force of 1 kg. If the accelerometer is properly calibrated, it will read 1 kg. 
If you repeat the experiment on the Moon, it will read -- roughly -- 0.166 kg. 
If we take the accelerometer and mount it in a space vehicle in free fall, it 
will read 0 kg. If we initiate a rocket burn, and the accelerometer reads -- 
while the motor is firing -- 1 kg, then we can state that our acceleration is 
equal to what we would feel standing on the Earth -- an acceleration of one 
'g'. Thus the extension of the spring is an exact analogue for the amount of 
acceleration being experienced. It relies for its operation on Newton's first 
law of motion and Hooke's law of
 elasticity.
 
There is another way we could utilise the accelerometer to determine our 
acceleration in a space vehicle. Let us assume again that we are in space in 
free fall and we are about to initiate a rocket burn. This time, instead of 
gluing our eyes to the accelerometer, we detach the 1 kg mass and place it 
outside the vehicle in free fall with velocities matched. We initiate our 
rocket burn, and with some radar or laser device we continuously measure the 
distance to the 1 kg mass. If we integrate the readings over time, we can 
calculate our acceleration.
 
Now for the crunch, the bit where our velocity changes due to acceleration by 
gravity. (Note - from a recent post from Regner, perhaps 'speed' is more 
appropriate here -- please comment if you think it appropriate. In any event, 
what I'm trying to convey is that our rate of travel increases). This time, we 
place our vehicle into elliptical orbit -- around Earth will suffice -- and as 
we pass apogee, we begin to accelerate. At this moment we place our 
accelerometer 1 kg mass outside the vehicle with velocities matched and engage 
our distance and time measuring devices. After we have passed perigee we will 
have stopped accelerating and begin decelerating. At no time from apogee to 
perigee will the 1 kg mass have fallen behind or overtaken us and this will not 
change from perigee back to apogee and so on for ever and ever amen. Despite 
acceleration and deceleration due to gravity in an elliptical orbit, our 
accelerometer will indicate no change in velocity.
 
Paul D


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