Fall Duration Calculator: Objects of Different Mass from 10m to 2m

[Luc B]

Hello Science Advisor Jbriqqs444

My question was: Are my calculations correct? About time of objects falling one to an other.
And i haven't still any answer.

About escape velocity, before making any calculation about speed (velocity), how many time need an object to go to the infinity.
An infinite time i think. And it will never be there.
So, is there any speed (velocity) whish send its to there?
I think not.
Am i rigth?

Thanks if you answer.

LucB.

 

[PeroK]

Hello Science Advisor Jbriqqs444

My question was: Are my calculations correct? About time of objects falling one to an other.
And i haven't still any answer.

About escape velocity, before making any calculation about speed (velocity), how many time need an object to go to the infinity.
An infinite time i think. And it will never be there.
So, is there any speed (velocity) whish send its to there?
I think not.
Am i rigth?

Thanks if you answer.

LucB.

If you fire something away from the Earth at a given speed, then either:

a) It eventually falls back to Earth

b) It doesn't (ever fall back).

The lowest speed at which it never comes back is the escape velocity.

 

[Luc B]

Hello Perok.
Thanks for this information...

Fire. You means "tirer" in french.
Do not forget the third low of Newton. action and reaction.
Specially if you are NOT on the earth. But on a very small planet.
And your gun is very big.

Luc B.

 

[PeroK]

Hello Perok.
Thanks for this information...

Fire. You means "tirer" in french.
Do not forget the third low of Newton. action and reaction.
Specially if you are NOT on the earth. But on a very small planet.
And your gun is very big.

Luc B.

Yes, "tirer". I would never forget Newton's third law!

The escape velocity is the relative velocity between the rocket and the planet. A normal planet hardly moves at all. For an asteroid, say, then it's definitely the relative velocity that you need. Not the velocity of the rocket in the original rest frame.

In any case, there is an escape velocity.

In fact, for a 1000 kg asteroid, you could easily jump off it and you would never come back to it. The escape velocity would be very low.

 

[Luc B]

Hello Perok.

I agree with you.
But what is the relative velocity between an asteroid of 1000 kg and a bullet of 1000 kg.
I know this forum is not to give answer but to help people.
My answer is: there is no velocity possible. The object fall always back. OR. Never reach the infinite.
Why. Because of the time, the infinite duration. Whish not exist.

Mathematic is a language. It is not physic.
Take an apple. Cut its in a infitive pieces.
What have you? An infinite of small, very small piece of apple.
Put them together. You have a cuted apple.Divide 3 by infiinity. You have nothing. And you don't respect the first low of thermodynamic.
Am i rigth?

Luc B.

 

[PeroK]

Hello Perok.

I agree with you.
But what is the relative velocity between an asteroid of 1000 kg and a bullet of 1000 kg.
I know this forum is not to give answer but to help people.
My answer is: there is no velocity possible. The object fall always back. OR. Never reach the infinite.
Why. Because of the time, the infinite duration. Whish not exist.

Mathematic is a language. It is not physic.
Take an apple. Cut its in a infitive pieces.
What have you? An infinite of small, very small piece of apple.
Put them together. You have a cuted apple.Divide 3 by infiinity. You have nothing. And you don't respect the first low of thermodynamic.
Am i rigth?

Luc B.

No, you are wrong.

If the bullet comes back, then it must come back at some (finite) time. Try to calculate that time and you'll find that there is no such time. Therefore, the bullet never comes back.

There is no need to take about "infinity".

 

[Luc B]

Hello gold member... Perok

Ok ok. I am wrong.

I think the bullet comes always back..
So in some (finite) time.
And the escape velocity doesn't exist.

But you say that escape velocity exist.
And your " colleague" Janus has given me how calculate its.
My computer said: 0.00036524 meter per second.
Is that rigth, according to you?

Luc B.

 

[PeroK]

Hello gold member... Perok

Ok ok. I am wrong.

I think the bullet comes always back..
So in some (finite) time.
And the escape velocity doesn't exist.

But you say that escape velocity exist.
And your " colleague" Janus has given me how calculate its.
My computer said: 0.00036524 meter per second.
Is that rigth, according to you?

Luc B.

Yes, that's right.

If you say the bullet comes back, then you have to give a time when it comes back. That's what it means to "come back". So, if you take a velocity of 0.000364 m/s, then you can say what time it comes back.

But, if you have a velocity of 0.000366 m/s, then the equation for the time that the bullet comes back has no solution.

And, if an equation has no solution, then it's not good maths or physics to say: eh bien, I don't believe that - it must have a solution! If there is no solution, there is no solution, and the bullet never comes back.

 

[PeroK]

@Luc B

Here's another way to look at it. Suppose you fire a rocket from Earth at 20,000 m/s (which is geater than the esacpe velocity). One thing you can calculate easily is how much the rocket slows down. In this case, the rocket never goes slower than 16,500 m/s.

So, not only does it not come back, but it is always traveling away from the Earth at more than 16,500 m/s.

 

[Luc B]

Hello Perok.

I think you are rigth.
I will make my own calculation tomorow.
It's sleeping time in my country.
I have had a "good" discussion with your "friend" Janus. About Eddington photographics en 1919 and a little experiment of Fresnel (+/- 1800).

{request for personal information deleted by a moderator}

See you tomorow.

Luc B.

 

[CWatters]

Cwaters. People has made calculations about solar system before we see Mercury problem..

You missunderstand what I was saying.

If you use an equation invented by someone you will get the same answer as that person. That does not mean they are 'correct'.
My point is that you cannot use

 

[Luc B]

Ok ok. CWatters

There are a lot of writers here. You and some others.
The same than in a french forum. The physics forum of the Liège University. And Sentinelle is a very important writer.
And all of you say that i am wrong.
Ok. I agree. I am wrong.
Are you happy? Is that rigth for you?
It is for me.
Time to sleep in my country.
See you tomiorrow, CWatters. Happy to know you.
Happy to have found someone who will say me "What to do".

Luc B.

 

[Luc B]

Ok ok Nidium

Do the calculation. If it is not so difficult.
And Thanks a lot.

Luc B.

 

[Dale]

Hello Dale

Ok ok. I will read it.
Did you make any analitic calculation?
To confirm or not my numbers?
I read it. In English...

Luc B.

The numbers are not the important thing. The relationship you found is the important thing:

What i found as duration surprise me.
More time for 1 and 10 kilos than for 5 and 10 kilos.
And the same time for 1 and 9 kilos than for 5 and 5 kilos.

This relationship can be obtained analytically using the reduced mass, Newton’s law of gravitation, and Newton’s 2nd law. It is super easy, you can probably do it in your head.

 

[Luc B]

Hello Dale

What i found is correct. Don't it?
And i come back with my conclusions. Whish are also correct. Following to me.
And may be, i am wrong. May be.

If we have the Earth. And nothing change about its. And there is an object of 100 kg that falls on it. It take more time than a object of 500 kg. I must be specific. Same height, Exactly same Earth. The same conditions. And the objects didn't come from the Earth. Aristote was rigth in - 350...
We have the Earth. And we take something from the Earth. And let its fall. Always from the same height. No matter the mass we take from the Earth to let its fall. It takes always the same time. And in 1600, Galilée was rigth in 1600.

But.

Now people think that all the objects fall on the Earth in the same way. And this is not correct.

Luc B.

 

[ZapperZ]

Hello Dale

What i found is correct. Don't it?
And i come back with my conclusions. Whish are also correct. Following to me.
And may be, i am wrong. May be.

If we have the Earth. And nothing change about its. And there is an object of 100 kg that falls on it. It take more time than a object of 500 kg. I must be specific. Same height, Exactly same Earth. The same conditions. And the objects didn't come from the Earth. Aristote was rigth in - 350...
We have the Earth. And we take something from the Earth. And let its fall. Always from the same height. No matter the mass we take from the Earth to let its fall. It takes always the same time. And in 1600, Galilée was rigth in 1600.

But.

Now people think that all the objects fall on the Earth in the same way. And this is not correct.

Luc B.

First of all, there is a language issue here, and it is a factor in deciphering what you are saying, and what you understood of what has been written to you. But be VERY careful in trying to push your own agenda. If you did not clearly understand the PF rules that you had read when you joined this forum, it might do you go to go back and re-read and UNDERSTAND those rules. They are strictly enforced.

Next, your claim is both correct and not correct, but it depends on the situation.

https://www.physicsforums.com/insights/why-is-acceleration-due-to-gravity-a-constant/

IF you are dealing with "g" being a constant, then ALL objects will fall at the same time. The mathematics describing the physics will prove this. However, once either the object is comparable to the size of the earth, or if one removes the constancy of "g", then one has to redo the calculation. I do not believe you have done the latter IF you are still under the assumption that "g" is a constant.

The infamous experiment of dropping objects of different weights and then hitting the ground at the same time are done on a terrestrial scale and with the explicit assumption that "g" doesn't change, which is a perfectly valid approximation. Classical mechanics in itself (i.e. your "calculation") is an approximation.

Zz.

 

[Dale]

What i found is correct. Don't it?

Yes

And i come back with my conclusions. Whish are also correct.

I don’t think so. You state your conclusion as a contest between people. As though they were wrestling or something and there can only be one winner.

Your conclusions are not only poorly stated as a personal contest, but they are also not logically connected to the calculation. A correct analysis would be to start with the same experimental scenario, identify the laws used by each person, determine the prediction for each, and compare the predictions to the actual results of the experiment.

The classical result is reached by using both Newton’s 2nd law and Newton’s law of gravity, so the conclusion clearly agrees with Newton. As far as I know, Galileo also used Newton’s laws, but I don’t know what laws Aristotle used.

 

[Luc B]

Hello
To Mr ZapperZ.
First. I have written: "And may be, i am wrong. May be". But i have seen no other number than mine. I am waiting for that. To compare.
Then, i have not made the calculation with g constant. I have made the calculation following the laws of Newton. Yes it is an approximation. Because i make my calculations by iteration. But it is very easy to control the precision. You can make the calculation with the maximum speed for each portion. And the minimum speed... And with excel, it is easy to divide the distance in 2 or 3000 portions...
But my calculations can be wrong...

To Mr Dale
Thank you for your reply.
BUT
Aristote lived round -350 (ante christum natum...). He was a thinker. He has said that our Earth was in the center of the universe. Motionless. And he had only his inner ear (oreille interne) to say that. And he had look to falling objects. And a stone goes faster than a leaf (feuille d'arbre). Aristote didn't use any law. Only his mind...
2000 years later, we are round 1600, Galilée began to teach young people in Pise, italy i think. And he was teaching Aristotle's ideas.....
And it is also said that he dropped stones from the top of the pisa tower. (tour de PIse, Italia). He had also no law for the gravitation effects.
And Newton came round 1700. And has written the tree laws. About gravitation, force and movement..............

F = G.m1.m2/d² F= m1 . a1 and F12 = F21. That all.

Perhaps, i am not sure. Your conclusions are NOT correct.

It is clearly impossible that Galileo has used the law of Newton...

Luc B.

 

[ZapperZ]

Hello
To Mr ZapperZ.
First. I have written: "And may be, i am wrong. May be". But i have seen no other number than mine. I am waiting for that. To compare.
Then, i have not made the calculation with g constant. I have made the calculation following the laws of Newton. Yes it is an approximation. Because i make my calculations by iteration. But it is very easy to control the precision. You can make the calculation with the maximum speed for each portion. And the minimum speed... And with excel, it is easy to divide the distance in 2 or 3 portions...
But my calculations can be wrong...

Please read the link that I have given you. Many of what you've stated in your posts have been addressed.

Unless you are solving a differential equation that produces a non-analytical solution, there is no extra benefit in solving this ".. by iteration..". My point still stands. If M_earth>>m_object on earth, then what is the big deal here? The physics shows that "g" can be accurately modeled as a constant. Do you think people who build houses consider the variation in "g" when they construct those buildings?

Zz.

 

[Luc B]

Ok. Ok. Mr ZapperZ

You are rigth. For the falling of object on Earth. From distance that human people use currently, there is not significant difference to use the Newton's Laws or a g constant.
And when Galileo said :"All object fall the same way on Earth". If we stay with objects on the human scale that fall from height also on a human scale, It's the truth.
I have made the calculations between objects of some kilo.
WHY?
Because i have NO computer that can make a différence between an object of 1 kg whish fall on Earth. And an object of 10 kg. I hope you understand why.
It is because Earth mass + 1 of 10 kg is always Earth mass for a computer.
With your raisonning, Jupitert falling on the Earth is the same than 1 kg falling on the Earth.
Sorry to shake your truths

Luc B.

 

[Janus]

Hello Dale

What i found is correct. Don't it?
And i come back with my conclusions. Whish are also correct. Following to me.
And may be, i am wrong. May be.

If we have the Earth. And nothing change about its. And there is an object of 100 kg that falls on it. It take more time than a object of 500 kg. I must be specific. Same height, Exactly same Earth. The same conditions. And the objects didn't come from the Earth. Aristote was rigth in - 350...
We have the Earth. And we take something from the Earth. And let its fall. Always from the same height. No matter the mass we take from the Earth to let its fall. It takes always the same time. And in 1600, Galilée was rigth in 1600.

But.

Now people think that all the objects fall on the Earth in the same way. And this is not correct.

Luc B.

In your examples, both the 100 kg object and the 500 kg object fall at the same rate. The difference in the time that they would take to strike the Earth is due to the difference in the rate the Earth falls towards a 100 kg object vs. a 500 kg object. The acceleration of both the 100 kg and 500 kg object will be 9.8 m/sec². The acceleration of the Earth will be 1.64e-22 m/sec² with the 100 kg object and 8.2e-22 m/sec² with the 500 kg object. Assuming a 100 m distance between ground and objects, the Earth will "fall" ~ 7.4e-22 m with the 100kg object and ~ 3.7e-22 m with the 500 kg object.
Both distances are extremely small (both are much smaller than even the radius of a single proton.)

But what happens if you drop them together side by side? Would the 500 kg object hit sooner (even if by only the tiniest amount)?, as Aristotle would have claimed? . No. both objects would again accelerate towards the Earth at 9.8m/sec². The Earth however cannot accelerate towards one object at a different rate than it does the other. Instead, it accelerates toward both objects at an rate determined by the sum of the masses of the two objects.

As an aside, the fact that dropped alone, a 100 kg object would hit a in infinitesimally longer time than a 500 kg object would is not a validation of Aristotle, as he believed that the 500 kg object would have taken a significantly shorter time to complete the fall.

 

[Luc B]

Hello Janus
You are right. Like you are also riht for Fresnel's spot.(He might see a thin ring of light surrounding the disk.)

But i am very interested for a reply of Mr Dale. About what laws have been used by Aristote?
And how Galileo had used the laws of Newton. A trip to the future?
He has said that i am wrong. Perhaps, he is right

Luc B.

 

[Dale]

Aristote didn't use any law.

And therefore he cannot be either right or wrong about the result of any calculation. Your conclusion regarding him is illogical.

Galilée ... He had also no law for the gravitation effects

Then he also can neither be shown right or wrong by a calculation or experiment. So again your conclusion is illogical.

Your conclusions are NOT correct.

I don’t recall making any conclusions.

He has said that i am wrong.

I didn’t say that you were wrong. I said that your argument is illogical. Irrespective of the correctness of the conclusion itself the conclusion does not follow logically from the computation.

 

[Luc B]

Hello Dale

I have written in the post Duration of a fall. Friday at 10:38 PM: Reply 45 :
"And i come back with my conclusions. Whish are also correct. Following to me.
And may be, i am wrong. May be"

And you reply: Reply 47
" I don’t think so. You state your conclusion as a contest between people. As though they were wrestling or something and there can only be one winner.
Your conclusions are not only poorly stated as a personal contest, but they are also not logically connected to the calculation. A correct analysis would be to start with the same experimental scenario, identify the laws used by each person, determine the prediction for each, and compare the predictions to the actual results of the experiment.
The classical result is reached by using both Newton’s 2nd law and Newton’s law of gravity, so the conclusion clearly agrees with Newton. As far as I know, Galileo also used Newton’s laws, but I don’t know what laws Aristotle used."

AND NOW. In the reply 53, you wrote:"I don’t recall making any conclusions." End of quote

Do you know how important is Galilean reasoning in the history of physics?
Reasoning that is still relevant today.
You are on the other side of the Atlantic. In a country that has become one of the great actors of the world. If not the most important.
Do you know that Italy was in Galileo's time?
And that France - it's not my country - was one of the countries where the great ideas of physics were shaped.
Sadi Carnot was French, Rudolf Clausius was German. But it is in Paris that he made these greatest conferences. Langevin, in 1911, in Bologna, Italy, gives his presentation in French .....
And Newton was English. It was translated during his lifetime. In French.

You conclude, it seems to me. When you say that Galileo used Newton's laws. It is temporally impossible.
But that means that you are a human being. And that you can go wrong. And rectify your mistakes.
But you do not remember having concluded.
This is a well-known phenomenon in the field of human behavior. Finally, if you accept this science as accurate.

Your "from here" writings are already available somewhere on the internet. I think you have the power to exclude me from this forum. I will defend myself with the means you will leave me.

Luc B.

 

[davenn]

You conclude, it seems to me. When you say that Galileo used Newton's laws. It is temporally impossible.
But that means that you are a human being. And that you can go wrong. And rectify your mistakes.
But you do not remember having concluded.
This is a well-known phenomenon in the field of human behavior. Finally, if you accept this science as accurate.

Your "from here" writings are already available somewhere on the internet. I think you have the power to exclude me from this forum. I will defend myself with the means you will leave me.

Luc B.

Luc
As an outsider reading through this thread, it has become very clear that...
you really need to stop talking and start listening to what is being said by the three people that have been responding to you
You have three very bright and well educated people trying to help you out and you are ignoring this help.
You would do very well to take what they are saying on the subject and start to understand it and to put you misunderstandings aside

If they ask you a question ( as has been done often), answer it specifically, DONT go off rambling about unrelated/irrelevant stuff ( as you have done often), clearly answer the question in a short and precise response.


regards
Dave

 

[Dale]

You conclude, it seems to me. When you say that Galileo used Newton's laws.

That was an (incorrect) assumption, not a conclusion.

I have no interest in the history. My point is that your stated conclusions are not logical. No amount of history lessons change that.

But that means that you are a human being. And that you can go wrong. And rectify your mistakes.

Sure. My assumption was wrong. Mistake rectified.

Now, will you rectify your mistake? To do so you could admit that your conclusions do not logically follow from your calculations, or you could show the laws used and their incompatibility with the calculation or the experimental evidence.

And what is with all of this obsession over nationalities? It is weirdly inappropriate for this forum.

 

[Luc B]

Hello Mr Davenn
Gold member

I have three very bright and well educated people trying to help me. Ok thanks for them.
I stop talking and writing here.
I take the last conclusions i have read as true.
Galileo use the law of Newton. That's all. OK OK OK. That's right.
I apologize for my ignorance.Sorry.

Luc B.

Post scriptum.
I have well read: reply 56 : That was an (incorrect) assumption, not a conclusion.....
There are a lot of assumption in physics which are not verified. But sure, i am wrong. Of course.

 

[Luc B]

Hello

I rectify my mistake; You are rigth Mr Dale
And if YOU use the laws of Newton. And there are: F=G.m1.m2/d² F12=F21= m1.a1=m2.a2
You will find the same time for every falls that have the same distance.
That are, i think, your logical conclusions.
And sure, there are right.

Thank you for your precious opinion

Luc B.

 

[Luc B]

Hello Mr Devann

I have three very brillant people who try to help me.
Ok. I have understood that.
And it is an obviousness for you that i have to change my raisonning.
But
You don't know anything about me.
If you read carefully, one of those brillant people made a mistake.
But no matter. They ARE brillant people...

When Don Christobal (Colomb) wanted to go trough atlantic ocean,
Very important people said him:" Eh Christobal. It is well knowed that it is impossible to cross the atlantic ocean
Don Christobal went trough atlantic ocean. AND CAME BACK.
But your continent is not called "Colombia'. But America. From Amerigo Vespucci.

Luc B

 

[Dale]

And if YOU use the laws of Newton. And there are: F=G.m1.m2/d² F12=F21= m1.a1=m2.a2
You will find the same time for every falls that have the same distance.

No. Remember that these equations are only valid in an inertial frame.