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Old 26th October 2008, 05:08 PM   #35
NobbyNobbs
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Originally Posted by Heiwa View Post
As JREF posters discussing the WTC1 collapse on the Pizza Box Tower thread don't know the difference between weight/mass (kg) and force (N) and moving bodies, let's do a new experiment in the bathroom in this thread and prove Bazant and NIST wrong, i.e. debunk them.
1st problem: weight is not the same as mass. Weight is not measured in kilograms, it is measured in Newtons. First week of high school physics.

Originally Posted by wikipedia
In the physical sciences, weight is a measurement of the gravitational force acting on an object.[1] Near the surface of the Earth, the acceleration due to gravity is approximately constant; this means that an object's weight is roughly proportional to its mass.

In commerce and in many other applications, weight means the same as mass as that term is used in physics.[1][2] In modern scientific usage, however, weight and mass are fundamentally different quantities: mass is an intrinsic property of matter, whereas weight is a force that results from the action of gravity on matter: it measures how strongly gravity pulls on that matter.

However, the recognition of this difference is, historically, a relatively recent development and in many everyday situations the word "weight" continues to be used when "mass" is meant. For example, we say that an object "weighs one kilogram", even though the kilogram is a unit of mass.
Source.

Originally Posted by Heiwa View Post
All you need is a bathroom scale! And a bathroom. And a ladder.

Assume you are in the bathroom and step on the scale and that it announces that your weight it 120 kgs (or what ever that is in US - 20 inches)! OK, you are only 160 cms (what is that - 3 lbs?) tall, so you are a small, fat weight, but who cares.
2nd problem: Your units continue to be wrong. First, your weight is not 120 kgs, that is your mass. Second, you are equating kilograms to inches. One is a unit of mass, the other a unit of distance. Then you compare centimeters (a unit of distance) to pounds, (a unit of weight)


Originally Posted by Heiwa View Post
Most Americans are overweight.
3rd problem: Gross (heh, heh!) generalization.


Originally Posted by Heiwa View Post
So far so good. Now the experiment. You are going to jump on the scale from 3.7 meters height and see, if your weight changes. Of course your bathroom has a high ceiling. Americans have big houses.
4th problem: Gross generalization.


Originally Posted by Heiwa View Post
OK, get the ladder into the bathroom and step up to the 3.7 m level. Don't knock your head against the ceiling.

Now jump on the scale!! WOSH, BANG!

What is your weight? Still 120 kgs! The scale records the same weight.
5th problem: The experimental evidence does not bear out this prediction. Have you tried it yourself? Obviously not.




Originally Posted by Heiwa View Post
Now a lot of people will say that your weight changed, when you impacted the scale, but it was 120 kgs before and after the experiment, so why would it change in between?
6th problem: You are undergoing a rapid deceleration when you hit the scale. The more rapid the deceleration, the larger the force required to cause it. When the ground (or scale) puts that force on you, Newton's 3rd law says you return that same force to the ground (scale). That is why your weight changes.

You are falling victim to the classic blunder that is the bane of middle school students everywhere. Your weight certainly changes. It's your mass that remains constant.



Originally Posted by Heiwa View Post
OK, but you normally do not measure your weight by jumping from 3.7 meters on your bathroom scale! So whatever you measure then, was not your weight.
7th problem: No, not normally. But you normally aren't falling onto your scale, either. But, in those instances when you are, your weight is more than it normally is, if only for a moment.
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