michel123456

The palm trees seem to be attacked there too as it appears in your 2nd photograph. I am afraid your superior being for this time is an insect

Yes, that could be a rephrasing of my question: Does the Fermat's principle apply to mechanical objects? Or only to waves?

I don't think polyurethane will do. Better get a cake recipe from your mother in law.

(emphasizing mine) Isn't that enough to put Snell's law at work? I mean, the slowing down of the bullet.

The first time I went on a Forum I didn't know it was a discussion Forum. I thought it was a Science Forum. A place where scientists share science. I was very naive. Then I got addicted.

1.When you shoot a ball against a wall, the object hits the wall and eventually rebounds following the laws of physics: if the wall is made of a perfect surface, the angle of incidence is the same as the angle of reflection. It is the same law that applies for waves. 2. When you shoot a bullet through a liquid (like shooting with a gun into a pound of water), will the bullet follow a path according to Snell"s law? Will the angle change when the bullet is in water?

I double the bet 6 letters FISCUS

I like bananas because they have no bones In french too That was very informative, wasn't it?

The methodology as described on page 63 of the linked pdf does not say that only christians were interviewed, but a range of adult americans. Maybe there is simply an increase of non-christians americans (muslims, hindus, etc.)

The discussion is not about relativity. At timestamp 3.26 he explains that "the cart will be accelerated relative to the Earth's frame" (3.38) At time stamp 5.48 he says "This is a strange Frame Of Reference" Yes I understand that. What boggles my mind is that here on Earth, we are indeed "in a strange Frame Of Reference". Let me explain my POV. Look at 4.45 What do you see? I see a ball moving sideways. I understand that the force that makes the ball deviates from the vertical is a fictitious force. I understand also (please correct me) that in the first place, the force that makes the ball fall vertically can also be a fictitious force. I understand that we call this force "gravity" but nonetheless this force shares the same caracteristics with the sideways fictitious force. Not to say that the cameraman in accelerated motion will feel the sideways fictitious force exactly in the same manner he feels gravity on Earth. So, IMHO it is wrong to state that there is no fictitious force on Earth. There is a fictitious force and we call it gravity. The only difference is in the orientation of the 2 forces. The one is pointed sideways, in the opposite direction of accelerated motion. The other one (gravity) is pointed towards the centre of the Earth. IOW, if both forces are fictitious, as I claim, then gravity must also be pointed in the opposite direction of accelerated motion. Which means that we are in an expanding Frame Of reference, and not in an Inertial Frame Of Reference. A "strange Frame Of Reference". ------------------------- Not to be misunderstood. I do not claim that the Earth is actually expanding at an accelerating rate 9.81 m/s^2. I claim that our FOR is expanding at an accelerating rate. I mean: everything that has mass.

I am almost deseperate not finding anywhere a video showing what I mean. Found this one Where the effect can be seen, if you make an effort, some yoga exercise first, and concentrate on what you are actually observing against what you are so used to observe. The train is constantly defomed since the front of the train is seemingly accelerated relatively to the back of the train, as you can observe when the train passes sideways. And this counts for constant motion. Still looking for something equivalent concerning accelerated motion.

In another thread, Swansont wrote As seen from someone standing on the ground, freefall means that the falling astronaut is accelerating towards the Earth. It seems obvious that the one on the ground and the falling astronaut are not in the same FOR, since one is accelerated towards the other. So I went looking back at the basics and found those old excellent videos In the second video, take attention after timestamp 4.00. In which it is stated that 1. The Earth IS an Inertial Frame Of Reference 2. An accelerated FOR relative to the Earth IS NOT an Inertial Frame Of Reference. Isn't an astronaut in free fall accelerated towards the Earth?

You have been contaminated

One should realize that our technology goes faster into the minuscule than into the enormous. Gigantism is part of human ambition from ancient times till today. It is not necessarily the way to into go to the future.

I will never stopped to be amazed by the way you describe extraordinary things as if it was common sense.

If i am not abused, in free fall the same happens. If you are in the toilets of an airplane in free fall, all your environment will have the same acceleration as you, which will give the illusion of lack of movement and lack of gravitation.

I don't know what space is. I don't know what time is. As a consequence, I guess I don't know what motion is. If you define motion as a displacement in spacetime, then you get caught because when you are at rest you still are getting displaced in spacetime. I guess again. Anyway defining motion as displacement or change in position doesn;t help much. What is your definition of motion?

Which means, if I am correct, that when you fall down, in fact what your eyes see is not a common accelerated motion towards the ground, but a second derivative of velocity. Which also means, If I am correct, that anything coming straight into your retina at constant velocity appears as being in accelerated motion.

You drive on the highway on a very long straight line. In the mirror, you look at a fast car coming closer and closer. Then the car comes really close and passes you by. Zouf. Then gently goes in front of you, getting smaller and smaller, slowly vanishing to the horizon. Don't you get the impression that the car was going faster when it was close to you? Maybe not because you have seen this effect so many times that it means nothing to you. The picture below. The real distance between the light posts is equal. Because of the effect of perspective, the apparent distance beween the posts (the colored lines on the picture) gets small and smaller until zero at the horizon. So, when you are observing a car moving at constant velocity in perspective, you are observing the car going from one post to the other in the same interval of time. IOW the car appears to travel less and less distance in the same time. Which is called deceleration. When you look at a car coming from the horizon and getting closer to you, you are observing the opposite effect: acceleration. Of course, that would be an abuse of language to call that "acceleration" because the car is moving at constant velocity. The "accelerated effect" is caused by the apparent deformation of perspective. However the effect is real and counts for everything coming from far away and reaching your eye. I wondered what is the mathematical relation between the coloured lines. Intuitively, a graph of it should be a conic section. A parabola I guess. Does anybody know?

So you concede it is all about observation, don't you? I don't know why you say that it doesn't work. It works (admitting distances are small- but then again absolute distance come in play). I agree (with Swansont) that it doesn't help much. You need some other tool to explain other kind of observations. Let's say I am ok so far.

At the time there exist a FOR in which _mass is invariant _length is maximum _time is mininmum There is a barrier, where things stop to change. That's where Relativity stops. It is another thing to say "everything is relative" and get masses from zero to infinity, lengths and times from zero to infinity, not telling you should insert negatives and get values from minus infinity to plus infinity. That kind of Theory I could accept. But not the one we have at hand.

Here is how i figure Relativity. You are observing and measuring a planet somewhere completely contracted. You send an astronaut aboard a vessel to go there and check. As the astronaut approaches, he observes (and measures) the planet less and less contracted. When arriving on the spot, the astronaut observes and measures the planet perfectly round. The question is: was the planet flat, skewed and round, really? Or was it round all the time long? IOW, is our Earth a flat disk, really, because some E.T. far away is observing us? That is how I understand Relativity. I say that you can only measure "true" length, mass and time from the same FOR of the object. Once you insert distance (as a comoving FOR), Speed Of Light will be involved and the machinery of Relativity will be at work, I guess. You'll have a lot of work to do. But thank you for trying.

You nailed it. Sincerely, after carefully reading all the arguments, I still remain on my interpretation. Hopefully, I will never teach Relativity to anyone so if I am wrong I will harm myself only. The fact is I cannot swallow how it is possible to be "normal" in one FOR and contracted in another and both situations be equally "real". To me there is only one single "reality". As you accept there exist an "invariant mass", I believe (yes it is a belief) there is a single "true" length that is the length one measures in the same FOR invariant mass naturally appears to be. The disappointing thing is that none of us was capable to put forward a decisive argument that could make the other change his mind. Could you provide a sketch? I cannot figure the situation. If the posts are skewed, then the meter stick must be skewed also. No? I mean, the situation must be perfectly symmetric.

Does that mean no mass or no mass? I mean, if he uses a speculative anti-gravity device, does that help?

You are correct. "Nice" is the correct scientific term, not "preferred", I apologize. This was sarcasm. The "value measured in the objects own frame of reference" is not simply that. It is also the extreme value (minimum or maximum). That is not negligeable. Maybe you can answer my question in post #55?