Re: [Phys-L] apparent weight

["John Clement" <clement@hal-pc.org>]

The accleration of the object closer to the Sun is greater because the
gravitational force is greater.  Of course this is ignoring the rotation of
the Earth which will also have to be factored in for a more exact
calculation.  That this is correct is easily seen by the tides.  At noon the
water is rising because the pull of the Sun/mass is greater on the water
which is closer to the sun than the Earth underneath.  Again this is a
simple model which should appeal to a beginning physics student and ignores
complications and second order effects.  The tidal forces are certainly
complicated by geography and the Coriolis pseudo force.

If the effect were the reverse, then when the sun and moon were at 90
degrees the tides would be greatest, but it is when they are lined up with
the Earth that you get the highest tides or what is often termed a "spring
tide".

I am curious as to the reasoning you used to deduce that the effect is the
reverse of what I claim.

John M. Clement
Houston, TX

> Defining the acceleration of the person as the time rate of 
> change of the velocity of the person relative to a reference 
> frame in which the sun is at rest at the origin and the earth 
> is orbiting the origin once per year, you have it exactly 
> backwards.  The person's acceleration is greater than that of 
> the center of the earth at midnight when the person is 
> farther from the sun, and smaller than that of the center of 
> the earth at noon when the person is closer to the sun.
>
> > The lighter scale reading will happen for both the Sun 
> above and the 
> > Sun below, just as the Moon produces 2 tides.  This simple analogy 
> > argument might be helpful with students.  The simple physics 
> > explanation is that since you are closer to the Sun when above than 
> > the center of the Earth, you have a greater acceleration toward the 
> > sun.  When the sun is below the Earth is accelerating more 
> towards the 
> > sun than you are because it is closer to the Sun.  In both 
> cases this 
> > results in a lower scale reading. I will leave the 
> complicated explanations to others, as they will confuse most 
> students.
> > Unfortunately most simple accounts of the tides ignore the 
> true effect 
> > and just talk about the pull.  It is a gradient effect.
> >
> > Of course a simple bathroom scale would be inadequate for 
> seeing this 
> > effect, and a gym scale which is a balance would show no effect.
> >
> > John M. clement
> > Houston, TX
> >
> >
> > > If you stand on a sensitive scale, will you be slightly 
> lighter at 
> > > noon (with the Sun above you and pulling opposite to Earth's 
> > > gravity), and slightly heavier at midnight (with the Sun 
> below you 
> > > and pulling in the same direction as Earth's gravity)? 
> Ignore any lunar effects.
> > > This came up the other day, and nobody could really agree.
> > > One side said no because the Earth is in freefall around the Sun, 
> > > and it is the Earth that pulls us to it. The other side 
> said yes due 
> > > to tidal effects as seen in the oceans.
> > >
> > > I searched online, and found the same conflicting arguments!
> > >
> > > Can anyone help with this?
> > >
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