funny thing about newton's laws. newton’s law of gravity was the gold standard in science for more than three centuries.
one morning old al einstein was sipping his coffee and thought, "damn. gravity doesn't work like that. sir isaac was full of crap. gravity works because a mass warps space. the stuff bends around a heavy body such as a planet for crying out loud." well not those exact words but you get the point. now stephen hawkings and others are beginning to question the great one's theory.

and there's this as regards a theory:


'a good theory will describe a large range of phenomena on the basis of a few simple postulates and will make definite predictions that can be tested. if the predictions agree with the observations, the theory survives that test, though it can never be proved to be correct.'

stephen hawking, the universe in a nutshell. no, i don't have a damn internet link. had to type directly from the friggin' book.

you're not in the least wrong actionlynx.

But you still won't admit you were.

The acceleration of gravity is independent of the velocity and mass.

g decreases by the square of the distance.

Two asteroids of UNEQUAL mass passing the Earth at the same speed and at the same distance from the Earth will hit the ground at the same time. They will also follow the same trajectory to hit the ground.

Good grief, the math is laid out for you from four different sources and you still bet on what "sounds" right?

Throwing words in the pot like Einstein and Hawking don't make Newton's laws any less true.

Depends upon who you ask...

No, Newton's Laws are always accurate to the same degree. You can get a tiny bit more precision if you calculate in Relativity, but it doesn't change the fact that the relationship between masses is inverse with distance and independent of mass.

Relativity effects only really matter when sufficient mass is present at sufficient density to seriously distort spacetime.

And in context to this conversation, the guys were abusing Newtons's laws.

The gravity posts make my head hurt.

It isn't necessarily intuitive, but the answer is that gravity impacts the bullet, ball, or rock you drop equally. When they say a bullet has a range of a certain distance...how do you think they figured that out?

This whole discussion reminds me of the "if you dropped a pound of feathers and a pound of lead from the Empire State Building, which would hit the ground first" riddle.

Sort of.

A smaller asteroids tend to break apart from an impact that might give it a high velocity, creating meteors instead.

You also have to consider the approach vector. Speed doesn't matter so much when the atmosphere is in its path. It's just going to get pulled down to Earth. That doesn't mean it will slow down. Just the opposite. It is likely to accelerate due to gravity....that is, until it enters the atmosphere, encountering drag, and hence achieving terminal velocity.

As far as slow-moving asteroids, my point was that they are less likely to even reach Earth. Even without considering the moon or Mars, the Earth still needs to be at the right point at the right time. Given the speed of the asteroid, the motion of the Earth, and gravity, a slow-moving asteroid could come within maybe 6,000 miles of the Earth and completely miss the planet. The distance is just a rough guess. I would have to calculate it out, but the point is that it could come much closer than the moon. If the Earth's orbit causes the planet to move away faster than the asteroid is approaching, then the asteroid is going pass right by.

Meanwhile, a fast-moving asteroid is much more likely to catch Earth at the right time, and to come at it before the Earth gets away. The approach angle, gravity, and velocity then come into play to decide whether it will hit, miss, or even get flung back out into space.

For reference, the orbital speed of Earth is 29,800 m/s compared to gravitational acceleration at Earth's surface of 9.8 m/s^2. That means an asteroid not only needs speed, but needs to be coming right at Earth. Acceleration due to gravity simply isn't enough, unless the space object can be pulled into an orbit where each pass brings it closer to the Earth. Even then, there is the chance the asteroid gets flung back out into space depending on its approach vector and velocity. More likely, just 1 or 2 degrees of the approach angle decides whether it will be a near miss or a hit.

For those that don't know, 29,000 m/s is about 64,370 mph. We're booking right along in space, making us a tough target to hit. Several factors have to come together just right for a collision to happen.

The 200 miles above Earth example is a case where a space mass comes extremely close to Earth. Most space debris that comes that close are small: man-made satellites, meteors, meteorites, and space dust. For a large mass, several thousand miles is considered a close call.

true. ask eingstein, if he were alive, and hawking and they'll tell you newton's law of gravity ain't no law no mo. in fact is was einsteins postulate regarding gravity that now is damn near universally accepted as debunking newton's law that put an end to naming theories laws in science as hawking explains so well in his many writings on the topic.

as the empire state building sits on earth which has an atmospheric pressure of 29.92 inches of mercury, standard day, the pound of lead will hit the ground first. yes, the force of gravity is equal on all things but gravity ain't the only force in action especially outside a vaccume.

they seem to forget that part...

I was kidding metal.

Shuck and jibe. You got the physics wrong, especially the gravity.

Maybe you should go back to your earlier posts on this thread and compare what you wrote to Newton's Laws of Gravity.

Einstein would get a good laugh indeed.

Actually you were right. It is amazing the answers you will get to any question.

Just for fun let's count the number of times the word "theory" occurs in the current Wilki description of this topic (as currently taught at MIT).

Newton's law of universal gravitation
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Classical mechanics
\mathbf{F} = m \mathbf{a}
Newton's Second Law
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Prof. Walter Lewin explains Newton's law of gravitation in MIT course 8.01[1]

Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. (Separately it was shown that large spherically symmetrical masses attract and are attracted as if all their mass were concentrated at their centers.) This is a general physical law derived from empirical observations by what Newton called induction.[2] It is a part of classical mechanics and was formulated in Newton's work Philosophiae Naturalis Principia Mathematica ("the Principia"), first published on 5 July 1687. (When Newton's book was presented in 1686 to the Royal Society, Robert Hooke made a claim that Newton had obtained the inverse square law from him – see History section below.) In modern language, the law states the following:

Every point mass attracts every single other point mass by a force pointing along the line intersecting both points. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between them:[3]

F = G \frac{m_1 m_2}{r^2}\ ,

where:

F is the force between the masses,
G is the gravitational constant,
m1 is the first mass,
m2 is the second mass, and
r is the distance between the masses.



Diagram of two masses attracting one another

Assuming SI units, F is measured in newtons (N), m1 and m2 in kilograms (kg), r in meters (m), and the constant G is approximately equal to 6.674×10−11 N m2 kg−2.[4] The value of the constant G was first accurately determined from the results of the Cavendish experiment conducted by the British scientist Henry Cavendish in 1798, although Cavendish did not himself calculate a numerical value for G.[5] This experiment was also the first test of Newton's theory of gravitation between masses in the laboratory. It took place 111 years after the publication of Newton's Principia and 71 years after Newton's death, so none of Newton's calculations could use the value of G; instead he could only calculate a force relative to another force.

Newton's law of gravitation resembles Coulomb's law of electrical forces, which is used to calculate the magnitude of electrical force between two charged bodies. Both are inverse-square laws, in which force is inversely proportional to the square of the distance between the bodies. Coulomb's Law has the product of two charges in place of the product of the masses, and the electrostatic constant in place of the gravitational constant.

Newton's law has since been superseded by Einstein's theory of general relativity, but it continues to be used as an excellent approximation of the effects of gravity. Relativity is required only when there is a need for extreme precision, or when dealing with gravitation for extremely massive and dense objects.

"A pound's a pound the world around."

Yes, but it begs the question: are the feathers dropped loosely, or are they bound together?

Feathers are designed to implement Bernoulli's Principle, using drag and low/high pressure to create lift. Hence, a pound of loose feathers will tend to fall slower than a pound of lead....under the right circumstances. Bundle them together, and it's a different story.

I bet both of you already knew that though, without stating it.

yes i know that well but having never seen feathers bound tight enough to equal the density of lead and seeing that the post never mentioned binding at all, just a pound of feathers, i think it's logical to assume he meant dropping a pound of unbound feathers. and bernoull's principle doesn't apply here necessarily. for the principle to work the feather would require airspeed. drag, in this case, causes the feathers to fall slower.

No, actually the Bernoulli Effect applies 100% of the time a falling object is in motion in the atmosphere. It doesn't matter if the object is of any shape or size. The Effect applies to objects in motion in an ideal fluid.

Okay that doesn't make much sense when you consider someone parachuting with and without an open parachute. They certainly don't hit the ground at the same time.

And free falling sky divers seem to be able to go faster and slower by the way they position and move their bodies.

It makes perfect sense if you understand how Bernoulli Effects work. Your points have nothing to do with it. Bernoulli described how pressures change with velocity in an ideal fluid.