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 Physics Forum Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

# Feather and hammer DO NOT fall at same rate!

## Feather and hammer DO NOT fall at same rate! - Physics Forum

### Feather and hammer DO NOT fall at same rate! - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.

#1
02-28-2005, 04:13 PM
 Dean Ware Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

Yes, GALILEO, was wrong!

OK, were on top of the tower of Pisa with Galilee Galileo.

After removing the earths atmosphere we drop the feather and time how long
it takes to hit the ground.

We do the same for the hammer.

We compare times and they are the same!

NOW, repeat the experiment, this time replacing the hammer with a neutron
star.

I would suggest that the neutron star would hit the earth (earth hit the
neutron star?) in less time than the feather, as the neutron stars
gravitational force pulls the earth towards itself.

Now the hammer has a gravitational pull on the earth too (more than the
feather does) so it would "fall" faster than the feather!

--------------------------

Any thoughts?

#2
02-28-2005, 04:42 PM
 Steve Ralph Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

"Dean Ware" <[Only registered users see links. ]> wrote in message
news:FiIUd.824\$[Only registered users see links. ].net...

Have you yet worked out how large a neutron 'star' would have to be to
be of comparable mass to a feather?
Have you considered that the feather will exert a gravitational force on the
earth? You can even work it out, but you will get a rather small number.

SR

#3
02-28-2005, 05:01 PM
Feather and hammer DO NOT fall at same rate!

Dean Ware wrote:

What did he say that was wrong?

long

Galileo (had he known of the effect of air resistance on the feather's
fall and the fact that a vacuum could be created) would have agreed.

neutron
the

OK. It is no longer the problem Galileo was working with. 'Apples to
oranges' and all that...

Why not rebuild the Tower of Pisa on the neutron star and drop the
feather and the earth from there?

the

Not noticeably. The time t to fall to earth from the height of the
Tower of Pisa s is given by solving the basic equation from dynamics:

s = (1/2)*a*t^2

where a is the acceeleration due to gravity.

Newton's Law relates this to the force F on the mass m by

F = m*a

and his Law of Gravitation gives is the force as

F = -G*M*m/r^2

where G is the universal constant of gravitation, M is the mass of thee
arth, and r is the distance from the top of the Tower of Pisa to the
center of mass of the earth.

solving these last two for a gives us the following:

a = F/m = -G*M/r^2

You will notice that the acceleration a does NOT depend on the mass of
the body being dropped from the tower. This is true as long as the
objects being dropped are insignificant in mass compared to the earth.

Granted this is a simplification in that it uses only Newtonian
mechanics. In General Relativity the equations and the results are a
little different, but because the height of the tower, the earth's
gravity, and the final velocity are all small by relativistic
standards, the differences between classical and relativistic
calculations are very small.

There are many people who *think* they have found an error in physics
somewhere. Most of them either can't or won't do the math. Some will
edo the math but are not able to see their own errors. [My late mother,
a retired proofreader, drilled me that editorial review is necessary in
all important papers because most people simply cannot see all of their
own errors, expecially those of oversight.]

And of course, some people are simply and clearly insane. You will see
all kinds in this group.

Tom Davidson
Richmond, VA

#4
02-28-2005, 05:09 PM
 N:dlzc D:aol T:com \(dlzc\) Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

It is a boondoggle. There is no gravitational force, and if you dropped
the neutron star (of any finite size), side-by-side with a feather in
vacuum, they'd both encounter the Earth at the same time. What is "raised"
by the neutron star (by a difference in mass), is raised for the feather
too.

Likely, the neutron star would subsume the feather, and they'd encounter
the Earth together anyway...

David A. Smith

#5
02-28-2005, 05:36 PM
 Morituri-|-Max Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

"Dean Ware" <[Only registered users see links. ]> wrote in message
news:FiIUd.824\$[Only registered users see links. ].net...

I would suggest you are a fool.. You can't trick your way past the
parameters of Galileo's experiment. What you are doing is no longer the
same experiment he did. If you are so dead set on details, I would also
suggest you wouldn't survive very long handling neutron stars with your bare
hands.

Again, you can't cheat the drill.

#6
02-28-2005, 06:46 PM
 OG Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

"Dean Ware" <[Only registered users see links. ]> wrote in message
news:FiIUd.824\$[Only registered users see links. ].net...
long
neutron
the
the

The acceleration is the same for the feather or the hammer, but the
distance travelled is less for the hammer.

Your title is wrong, because you have confused falling 'a shorter
distance' with falling 'faster'.

#7
03-01-2005, 01:29 AM
 Dean Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

> What did he say that was wrong?

That if you drop a feather, it will take the same time to "fall" to the
bottom of the tower as a hammer would.

This is WRONG.

Basically, because "falling" is in actuall fact objects moving towards
each other due to MUTUAL gravitational attraction. In this case one of
the object (the earth) moves a lot less then the other object (the feather)

OK, lets imagine that we take a SMALL neutron star. Say a neutron star
the mass of a hammer.

We drop THAT from the top of the tower of pisa.

And measure the time it takes for it to strike the earth.

Now we take a slightly more massive neutron star and time that.

We repeat this for larger and larger neutron stars.

Eventually we will have a neutron star whose acceleration due to gravity
at the height of the tower of pisa (and therefore the distance to the
earth) from its surface is 100,000 m/ss

The earth and the largest considered neutron star will collide FAR
FASTER then the earth and a feather.
Agreed?

Now at which point from the hammer-mass neutron star to the final huge
neutron star do you say the "situation has changed" and its "Apples and
Oranges"?

Fundamentally we are considering the

#8
03-01-2005, 10:46 AM
 Mike Yarwood Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

"OG" <[Only registered users see links. ].uk> wrote in message
news:[Only registered users see links. ]...
If I remember correctly, I was told that Galileo dropped balls of different
weight and then said that if he dropped two balls of different weight at the
same time they would hit the ground at the same time - seems o.k. to me
provided that the ground was level.

Best of Luck - Mike

#9
03-01-2005, 11:16 AM
 PD Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

Dean wrote:
the

Yes, you're right. You're also picking nits. The claim Galileo made was
made in the context of a highly massive Earth that did not
substantially move as a result of gravitational interaction.

Note that what is conventionally said as a RESULT of Galileo's
observation is that the acceleration of a body due to gravitational
interaction does not depend on the mass of the falling body.

In the case of feather and hammer falling to Earth, a common
acceleration would amount to (essentially) the same *time* to fall.

PD

towards
of
feather)
hit
to
star
gravity

huge
and

#10
03-01-2005, 11:31 AM
 Steve Ralph Guest Posts: n/a
Feather and hammer DO NOT fall at same rate!

"Dean" <[Only registered users see links. ]> wrote in message
news:jsQUd.537\$[Only registered users see links. ].net...

You are going to need a lot of hammers.

SR

 Tags fall , feather , hammer , rate

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