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I'll lead off with this snippet:
By applying a force of one Newton, one can hold a body ...
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By applying a force of one Newton, one can hold a body of mass a. 102 grams, correct to three significant figures.
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Newton's third law states that every applied force has an equal but opposite reaction force. In our case, we have a body of mass m being held in air by ...
102 grams isn't much.... a can of tuna I found in the cupboard weighs 142 grams.
A bag of Ramen Noodles is 85 grams .
This topic is available if anyone else can find something closer to 102 grams at sea level.
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The Newton is the unit of force defined in terms of the kg of mass, meter of distance, and second of time. One standard kg exposed to a gravitational acceleration of only 1 m/s^2 would weigh 1 Newton. Here on Earth, 1 standard kg of mass exposed to a gravitational acceleration of 1 standard Earth gee (some 9.80667 m/s^2) weighs 9.80667 Newtons. Check the definitions in SI if you don't believe me.
There's non-SI metric units in wide use, and the kg-force and the metric ton-force are a couple of them. The kg-force is the Earth weight of 1 std kg of mass exposed to one standard gee of gravitational acceleration. 1 kg-force = 9.80667 Newtons. Likewise, the metric ton-force is the Earth weight of one standard metric ton (1000 std kg) of mass exposed to 1 standard gee of gravitational acceleration. 1 metric ton-force = 9.80667 Kilo-Newtons. A lot of torque wrenches are calibrated to read in m*kg-f units, not the SI m*N units.
The existence of the kg-force (kg-f) unit is exactly why specific impulse is measured in seconds. It is kg-f of thrust divided by kg/s massflow (not weight flow !!!!). People "conveniently" divide-out kg-f with kg, although that is not right! Similarly, Isp = metric tons-force divided by metric tons of mass per second, dividing-out the metric ton-force with the metric ton, although that is not right, either. This was defined long before SI, by many decades.
The analog to this in US customary units is Isp = lb of thrust divided by lbm/sec of propellant flow, yielding sec if you divide-out lb with lbm, which isn't right. That is where the lbm is defined in terms of the lb force unit, feet, and seconds, improperly as the mass that weighs 1 lb at 1 standard Earth gee of gravity, which is really 32.174 ft/sec^2. The lb is the Earth weight of 1 lbm of mass.
Just goes to show you that the evils men do live long after them.
GW
Last edited by GW Johnson (2024-12-13 17:27:40)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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