michel123456

I agree. But be careful no to change it in a too fancy way. As for your "learning assistant", that sounds great for you. But be careful not to enter naively the real world abruptly. Maybe there were some cuttings in staff in your University, maybe you are going to steal someone else's job. I guess you are not paid for this. You must know a synonym for unpaid employment. How is it possible to argue that an inexperienced teacher is better than an experienced one? Note: at my times (again) some professors used students to help them in their private office, or even used to bring their private work as a theme of study at the University. Of course it was considered as an honour to participate because professor choose only the best students. Unpaid of course. Shame.

Because the direction of the ball is perpendicular to the 2nd ramp. The rebound will be in the reverse direction.

I don't think that the origin of the arrow has anything to do with cosmology. To me the arrow is deeply hidden into existence. The arrow is linked to gravity.

Yes. Anyway the error is mine. The first diagram is intentionally wrong. I simply wanted to show the importance of drawing an accurate diagram. And also to relativate all blind mathematical conclusions.

That is right. Angle. I mean right angle. The correct drawing is here below The ball will never go up, it will collide against the 90 degrees angle. That is because the sum of the angles 48 + 42 = 90, then the resulting angle between the ramps is also 90. All this to show that a good sketch is indispensable. Resolving mathematically the problem induces an error, especially when based upon a wrong sketch.

Sorry but i still don't get it. In my times at 19 I was considered as a beginner who knew nothing.

I don't understand the above. What do you call an "assistant"? Is it "Assistant Professor"? Don't you need a PhD for such a position?

Wrong answer. Hint: we are in the brain teasers & puzzles section.

Cap'n, are you really 19 years old?

IIRC standard cosmology states that space is expanding at an accelerating rate, not proper motion.

A ball A is placed on a ramp of 48 degrees. What max. height F and distance C will reach the ball, excluding any friction? The ball is 3 kg weight, 20 cm in diameter. Note: this is not homework.

Emergency doors have a mechanical release actioned by the push handle. The electromagnetic system is used for doors that are constantly open and automatically close in case of fire to create a fire compartment. I suppose anodised aluminium is used because no paint is needed. Paint on handles gets scratched very quickly. You paint steel also, except stainless steel which is more than twice more expensive. Another solution is chrome, but it gets oxydized quickly if the support is not good. A good support is brass but it is expensive too.

No, I simply made a sketch at scale and the 3 4 5 triangle came out quite naturally. I have learned to always try to make a sketch of any problem, even for non geometrical ones. In many case you see the solution very quickly. The algebraic way to get there has almost no interest to me: when you know the start and you know the end, the travel is only a matter of work and patience. edit. And also I cheated & got help from wiki after searching for integer triangle edit2 I also tried to solve by adding one unit on the AB side & one unit on the BC side. Then you get a new triangle A' C' D inscribed in a circle of radius 10, the new angle at D is orthogonal by definition. The small added triangles have a surface of 1h. But I could not get further, the 345 triangle was much easier. After 15 min. if I don't find a solution, I quit. No patience anymore.

You're the best.

There is also an intuitive way. Because there are no many known triangles with all 3 sides composed of integers, like the BCD triangle here with sides 9 17 10 respectively. Have you learned the 3 4 5 triangle? ------------------ I guess your professor will subjugate the classroom prooving in 2 steps that h = 8. Then that the surface of BCD is equal to its perimeter. He must have read MacHale, D., "That 3,4,5 triangle again," Mathematical Gazette 73, March 1989, 14-16. Or he has access to Wikipedia.

You will find an old new here. -------------------- Cities may change. Most probably mobility will decrease because working at home will increase. If all goes well. What will not decrease is the amount of goods to transport. I remember studies about subways for supplies (not for people). I'll have to search a bit if you're interested. ------------------- In my country, we are seriously thinking about introducing the ecological vehicule of tomorrow: the donkey.

Proposition: Is it possible in the thread list to put the creation date of a thread (next to or below the "started by"). It would be informative.

My preferred one God created man as His image. ......................................... Afterwards man evoluted, God...Him, we don't know. Drawing from P. Geluck

Isn't it about emergency exit doors?

Yes it is.

True. The question was not upon that point though. Maybe it was not even a question but a simple misunderstanding. What i said was that the key was a single object, statement on which Iggy agreed because he wrote: As a consequence, i stated that the object, the key, changed spacetime coordinates, statement on which I suppose there was no ambiguity. And as a final consequence, I stated that if there was only one & single object, and that this object changed spacetime coordinates, it could not occupy both coordinates "at the same time". This last statement introduces a confusion that I am aware of, and Iggy disagrees because I introduced maliciously a fifth dimension. It is a pleasure disagreeing with Iggy because he makes his point clear without shouting. But we still disagree. As for your remark, it is perfectly correct: a hypothetical time traveler should not only travel through time but also through space.

What we call the arrow of time is a phenomena of asymmetry. Out of entropy there are other physical concepts that are non symmetric, we simply tend not to pay attention about it. For example, distance is a measurement that is always positive by definition. Talking about negative distance is the same insensitive as talking about negative time. Another example is gravity, which is always positive as far as our direct observations are concerned. That is a good reason IMHO to consider that all those exclusively positive concepts (time, distance, gravity, entropy) should be connected by a single explanation.

oops sorry. again. I made a bad comment caused by confusion of your [math] a^{\left \langle n \right \rangle}[/math] notation different from [math] a^n[/math]

The most funny thing is that if what we observe came to us at 3.3 times the SOL, what we see is not the past, it is the future

There is something about the Laws of Nature. And there is something missing in our laws of physics, for sure.