Comments for Hammer and Feather

Comment on Wrong Way Round by Reid Penner

Reid Penner — Tue, 03 Nov 2009 07:06:57 +0000

I think its a very interesting observation, but i don’t think its as big of an issue as you think it is.

Granted, my math shows a peak acceleration of 8.7 g of the S IVB, which is of similar design, and uses the earlier J-2 engine, according to wikipedia (i know, it can be unreliable, but i think it can still hold valid info), the EDS will only be throttled up to 80% for TLI. By my math, that still puts it at 7 g, at maximum acceleration. ( assuming the tanks are burnt dry)

http://en.wikipedia.org/wiki/Earth_Departure_Stage#Mission

I’m no expert on the matter either, but remember that these accelerations are maximums, and should be expected only near the end of the burn. Therefore, in my humble opinion, i think that the reverse seating is not a major issue. (The burn time of the S IVB was also only around 8 minutes, as well)

Comment on Why Hammer and Feather? by saturn5

saturn5 — Fri, 14 Aug 2009 08:56:21 +0000

As an object falls in an atmosphere acceleration decreases from an initial 9.8 m/s/s as air resistance increases due to increased speed, speed increases until it reaches a terminal speed where forces of weight and air resistance are balanced.

Where there is no atmosphere the speed increases at the rate of local g, with no terminal speed. On the Moon this is about 1.6m/s/s.

This is best illustrated with s/t or d/t graphs. I’m sure you can find them if you look in your textbook.

You appear to be uncertain of the meanings of speed/velocity, distance/displacement.

Comment on Why Hammer and Feather? by Sboniso percival

Sboniso percival — Fri, 14 Aug 2009 08:22:23 +0000

when an object is falling freely, what happens to the acceleration ,velocity, displacement , speed and distance of the object as it is falling?

Comment on Why Hammer and Feather? by Sboniso percival

Sboniso percival — Fri, 14 Aug 2009 08:17:11 +0000

Hi i am Percival i am glad to known that the abject will move at the constant velocity unless they is an unbalance force act on it e.g it means that if you got a ball you can throw it in a straight line it will move if the air resistance doesn’t act on it like net force,gravitational force it will continue to move at constant velocity in a straight line.

Comment on Why Hammer and Feather? by Sboniso percival

Sboniso percival — Fri, 14 Aug 2009 08:01:42 +0000

This the one of those important things in the world of science to what was happening in the world in the 20s and the 70s till now. this information it helping us as the science student to known feather about science.

Comment on About by Ray

Ray — Tue, 30 Jun 2009 01:16:53 +0000

Wont it be awesome when one day, a future astonaut finds Dave’s hammer and feather? I hope the knuckleheads who pretend the Apollo landings were hoaxed are still alive to see that happen.
~ and me too, come to think of it.

Comment on First Man by Neil Armstrong interview « Hammer and Feather

Neil Armstrong interview « Hammer and Feather — Sat, 25 Oct 2008 18:41:22 +0000

[...] I’ve previously written about James Hanson’s biography of Armstrong, First Man. I recently found this CBS 60 Minutes profile of Armstrong broadcast to mark the publication of [...]

Comment on Hammer & Feather II by saturn5

saturn5 — Mon, 22 Sep 2008 11:58:51 +0000

…as for G, that is the universal gravitational constant, and is the same whatever body you consider, be it planet or feather. The equation you quote gives the force between two objects a certain distance apart, so was appropriate for working out the force between the hammer and the Moon, say. More usually it is used to calculate the force between planets and the Sun, or between the Earth and the Moon.

The value of G is approx 6.67×10^-11 m^3kg^-1s^-2. Look it up at Wikipedia.

Comment on Hammer & Feather II by saturn5

saturn5 — Thu, 18 Sep 2008 21:43:07 +0000

Hi Doug. I’m not sure I understand your problem here, but let me try. As you can see from the video (or by repeating the experiment in vacuum on Earth) the objects (whatever they are) do fall at the same rate. You go back to Galileo and Newton here. Galileo’s famous demonstration with cannonballs showed that, although there was a tiny difference in times of landing due to air resistance, there wasn’t the big difference that Aristotle et al had asserted.

Newton explained that F=ma (2nd Law). Simple really – is this where ‘masses cancel out’? Two objects – say 1kg and 10kg – fall. The 10kg mass is pulled 10x harder than the 1kg mass. But the 10kg mass is 10x harder to accelerate. So the acceleration is the same for both as a result – they both fall at the same time. a=F/m.

It’s safe to consider only one side of the system and ignore the Moon or Earth here as ‘each force has an equal and opposite force’ – 3rd law. The Moon/Earth will of course accelerate toward the dropped object, but due to the enormous mass difference the acceleration is very tiny (the force between them is the same). So the difference in acceleration is in fact massive, not, as you say very small.

Don’t know why you’d need the equation you quote or need to know g (or G) for the hammer. Good old F=ma is all you need. If you want to know how big the acceleration due to gravity is, that’s g (Earth 9.8m/s², Moon 1.6m/s²). Doesn’t matter what you drop, that’s how fast it accelerates, if you can ignore air resistance (as you can, of course, on the Moon). Strictly, it is how fast the Moon and the hammer accelerate together, but, as I say, you can ignore how much the Moon accelerates as it is negligible.

Does that answer your question, whatever it was?

Comment on Hammer & Feather II by Doug

Doug — Thu, 18 Sep 2008 18:26:32 +0000

Does anyone have a reference to a site that will explain the math behind this assertion that the hammer and the feather fall at the same rate. I don’t buy it. They appear to fall at the same rate becuse the earth (or moon in this case) is the largset contributor to the gravitational attraction, but the reality is that when the feather and hammer are dropped, the moon is moving toward the hammer and feather at one rate (based on the combined weight of the hammer and feather) and the hammer and feather are moving at a different rate. I realize the difference is very, very small, but still I think the argument is and has always been inaccurate. btw; I did the whole calculation in physics calss where the masses cancel out, but this was ignoring the fact that G and g are not the same thing and also very conveniently used the formula Fa = Gx(m1xm2/r^2) where G is the gravitational constant for the earth (or moon)…but G for the feather and hammer are conveniently left out. The only thing this feather and hammer question answered is..if you can dictate an answer by how you ask the question.