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How far does an object fall during the first half second after it's released?

How far does an object fall during the first half second after it's released? - Physics Forum

How far does an object fall during the first half second after it's released? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #1  
Old 06-30-2004, 09:01 PM
Donald G. Shead
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Default How far does an object fall during the first half second after it's released?



Hint: Galileo found that objects free fall at a rate of (about) 16
feet per second, per second:
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  #2  
Old 07-01-2004, 01:35 PM
The Ghost In The Machine
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Default How far does an object fall during the first half second after it's released?

[Followups set to sci.physics.]
In sci.math, Donald G. Shead
<[Only registered users see links. ]>
wrote
on 30 Jun 2004 14:01:22 -0700
<[Only registered users see links. ] >:

Plus or minus 0.2% - 0.25%. The weight of an item might
be 1000 N at the equator, but only 996 N at the poles.
(As always, the weight divided by the local g -- mass --
is constant; most people of course simply assume mass (at
rest) is constant and don't bother going this direction.)

--
#191, [Only registered users see links. ]
It's still legal to go .sigless.
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  #3  
Old 07-01-2004, 06:48 PM
Donald G. Shead
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Default How far does an object fall during the first half second after it's released?

The Ghost In The Machine <[Only registered users see links. ]> wrote in message news:<[Only registered users see links. ]>...

Virtually all good weight-scales, _if set to zero when empty_; in the
controled environment of a laboratory: Whether at the equator or the
poles will register the same weight for any item!
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  #4  
Old 07-02-2004, 08:00 AM
The Ghost In The Machine
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Default How far does an object fall during the first half second after it's released?

In sci.math, Donald G. Shead
<[Only registered users see links. ]>
wrote
on 1 Jul 2004 11:48:39 -0700
<[Only registered users see links. ] >:

That's because they're not weigh-scales, but mass-scales (or
counterbalance-torque-scales). Do I really need to explain
this again?

Assume a standard doctor's scale. (You're probably old enough
to require regular visits thereto, although I'm not at all sure
such scales are still in use anymore in doctor's offices.
But never mind.)

[----]---*--o--v---------v--------[v]--------v---------v---------v----[]
|

The above is a schematic representation of part of a
doctor's scale. At the far left is a counterweight, used
for zeroing; this counterweight is usually adjustable by
twisting it, as it's on a screw. To its right ('*') is
a point of joining, going down to the standing-platform;
this is probably attached by a nut and bolt, or a rivet,
depending on how cheap the scale is.

To its right ('o') is the pivot point itself. This pivot
point allows the entire rod to freely tilt up and down,
within the limits of the guard ('[]') at the extreme right.
The rest of the rod is given to allowing a sliding weight
(shown as [v] above, where it's stuck on one of the indentations)
to move reasonably freely.

Now, everything has a weight here (including the bar
itself); each weight, which manifests as the usual downward
force, imparts a torque on the pivot point. If the scale
balances, the sum of all torques is effectively zero.
Properly constructed, with a properly zeroed counterweight,
this scale will accurately read *mass*. Of course one can
do silly things like place a magnet under the counterweight,
then ship it to the moon -- but absent the magnet, the readings
for a given mass will be the same on the moon as they would be
on good old Earth. It might even work on an asteroid, although
one might have to wait a significant amount of time to ensure
that the bar is balanced and the mass is correctly positioned.

Now hopefully you remember what a torque is: it's distance
times force perpendicular to the torque-arm.

If that's too hard for you, you can consider the pan scale, instead.
The pan scale works in a very similar fashion, assuming good
construction (the main issue is that the distances between the
pivot and the pan attachment points are equal).

*-----o-----*
/ \ / \
/ \ / \
+-----+ +-----+

Proper usage of the pan scale involves a set of reference masses.

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  #5  
Old 07-02-2004, 08:00 AM
The Ghost In The Machine
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Default How far does an object fall during the first half second after it's released?

In sci.math, Richard Henry
<[Only registered users see links. ]>
wrote
on Thu, 1 Jul 2004 12:47:47 -0700
<HTZEc.6180$151.4316@fed1read02>:

Shead is apparently hopelessly confused on the matter.
I would hope that good lab-scales would accurately show
*mass* and indicate the same *mass* whether they be on an
equatorial lab bench somewhere in the tropics, or sitting
in the heated lab bench of an Arctic icebreaker or an
Antarctic lab constructed on the ice (assuming that the
reference masses are warm enough to avoid condensation of
water vapor -- although somehow I doubt there's that much
to condense anyway, within the lab itself).

--
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  #6  
Old 07-02-2004, 12:37 PM
Donald G. Shead
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Default How far does an object fall during the first half second after it's released?

"Richard Henry" <[Only registered users see links. ]> wrote in message news:<HTZEc.6180$151.4316@fed1read02>...
Cut<

Will you please tell me why they don't.
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  #7  
Old 07-02-2004, 12:46 PM
Gordon
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Default How far does an object fall during the first half second after it's released?

On Fri, 02 Jul 2004 08:00:27 GMT, The Ghost In The Machine
<[Only registered users see links. ]> wrote:

Are you saying that such scales, if positioned with the scale's
platform in a vertical plane, and the scale's base backed against
a firm surface such as a wall, then a horizontal force applied to
the scale's platform would produce an indication of mass?

Scales measure force. In most cases it is the resultant
gravitational force between the mass of the earth and the mass of
some object being weighed, but in any case, it is the force that
is measured.

A balance will measure mass, by comparing a known mass to the
unknown mass being evaluated.
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  #8  
Old 07-02-2004, 01:02 PM
Sam Wormley
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Default How far does an object fall during the first half second after it'sreleased?

"Donald G. Shead" wrote:

w = mg

g has different values at different altitudes and different locations
on the Earth at the same altitude. This is a problem for spring scales.
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  #9  
Old 07-02-2004, 02:20 PM
Donald G. Shead
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Default How far does an object fall during the first half second after it's released?

The Ghost In The Machine <[Only registered users see links. ]> wrote in message news:<[Only registered users see links. ]>...
Cut<

These masses exert weight-force on one pan; to the extent that they
require an equal weight-force on the opposite pan.
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  #10  
Old 07-02-2004, 03:22 PM
Donald G. Shead
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Default How far does an object fall during the first half second after it's released?

The Ghost In The Machine <[Only registered users see links. ]> wrote

These reference "masses' are material objects, or bodies of matter of
various small sizes, manufactured to exert exact weight-forces; to act
as counter-weights on balance scales, and more often than not (?), for
convenience are simply called weights: Usually with a preceding
number; as 1 ounce, 1 pound, 2 pound 5 pound or 10 pound weight.

Ask the people who use them; in or out of laboratories around the
world.
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