[Momentus (OP)]

This really does make my case for me.

Your example was about an elastic collision and not about a centripetal force.

Consider if you can, if you are able to, a case where a force of which you approve, which meets your unstated yet specific needs is exerted on a moving body, perpendicular to the motion of said body, just like Sir Isacc Newton proposes in the passage I have already quoted for you.
Ignore all my ignorance cess pit garbage and nonsense, if you can, and answer the very simple question.
Perpendicular force does not change the magnitude component of velocity. it changes the direction and only the direction.
A simple answer of yes or no, with some outside reference will be appreciated. Teach me O guru of science

[Momentus (OP)]

Your big misconception is that you have got it in your head that a perpendicular collision of a moving object cannot change the speed of that object, which is wrong.  You seem to have gotten that impression because of how a centripetal force works.  I will say the obvious once more; a collision and centripetal forces are 2 different things.   

Is there really no one reading this with the courage to call this Naked Science King out on this nonsense

[Bored chemist]

Perpendicular force does not change the magnitude component of velocity. it changes the direction and only the direction.

Well, here's my take on it:

That's still more or less guaranteed to be wrong..
If a force acts on something it changes the momentum of the thing.
In one odd sort of case it may change just the direction.
That case is when you have something like a mass being swung round on a string.
But that's not the case you drew in your OP.

The reason that the " mass on a string" case is different is what happens if you consider the moments (periods of time not the thing related to torque) just before and after the time when it exerts a perpendicular force. Here's a bad picture
BAD PICTURE.png (8.51 kB . 591x425 - viewed 361 times)

It shows the circular path of a mass traveling clockwise (as indicated by the arrow) at three instants in time T1, T2, T3. It also shows the force (acting towards the centre) at those times F1 F2, F3.
As I said, it's a bad picture, please pretend that at T2 the line from the centre to the body is vertical.
At T1 there's a component of the force F1 acting horizontally  left to right.
And at T3 there's a component of the force F3 acting horizontally  right to left.


As you make the time intervals between T1 and T3 small enough those two horizontal forces tend to cancel out.
And, for zero time they exactly cancel. The only force acting is in towards the centre of the circle. But only for zero time.

You can do that if you have a bit of string or something.
But you can't do it with colliding bodies because there's no opportunity of the sideways forces to be averaged out to zero

Which is why I asked this

What is the difference between something that does not happen, and something that can only happen if you do something  impossible?

It's a pity you didn't think to answer that at the time.

Because it's the distinction between the case of an object moving in a circle- like Newton described- and the case you drew in the OP.

That's why he's right and you aren't.


And the whole of this offshoot of the tread should be moved to the other thread, rather than this one about how much clutter there is in "New Theories"

[paul cotter]

The only who is talking nonsense is you. You may have read Principia but you certainly did not understand it. There are some highly competent people on this forum( way, way ahead of me ) and none of them agrees with your erroneous ideas. What does that tell you? Courage is not at issue, the aim here is to promote truth.

[Bored chemist]

Is there really no one reading this with the courage to call this Naked Science King out on this nonsense

I have plenty of courage.
But... he's right.

[paul cotter]

Momentus, we have told you repeatedly that a force acting at 90 degrees to a travelling object can transmit any arbitrary momentum to said body and hence change it's speed in the direction of said force but it will not affect the component of speed that the object originally had, ie that at 90 degrees to the applied force. If you cannot understand this you need to educate yourself in basic mechanics.

[Origin]

Is there really no one reading this with the courage to call this Naked Science King out on this nonsense

Let's do a quick check to see who is talking nonsense.

First and foremost we know that in an elastic collision the KEi = KEf.

The KE before the collision.
Assume the velocities are m/s.
Assume the masses are 1 kg (to make it easy and clear)
Blue ball:  1/2m*v^2 = 1/2(1 kg)*(4 m/s)^2 = 8 J
Red ball:  1/2m*v^2 = 1/2(1 kg)*(3 m/s)^2 = 4.5 J
Total KE = 8 J + 4.5 J = 12.5 J

KE after the collision.

Blue ball:  I say the x component of the velocity is 4 m/s and the y component of the velocity is 3 m/s, this gives an overall velocity of 5 m/s.

You say the x component of the velocity is 2.6 m/s and the y component of velocity is 3 m/s, this gives an overall velocity of 4 m/s.  (A 2.6 m/s velocity in the x direction does not give an exact overall velocity of 4 m/s, but it is close enough).

We both agree that the red ball is stationary.

So the KE after the collision should still be 12.5 J.

Red ball:  1/2m*v^2 = 1/2(1kg)*(0m/s)^2 = 0 J.
Your numbers, Blue ball:  1/2m*v^2 = 1/2(1kg)*(4m/s)^2 = 8 J.
Total KE:  0 J +8 J = 8J
KEi = 12.5 J
KEf = 8 J
For your numbers KEi ≠ KEf.
Your answer cannot be correct.

Red ball:  1/2m*v^2 = 1/2(1kg)*(0m/s)^2 = 0 J.
My numbers, Blue ball:  1/2m*v^2 = 1/2(1kg)*(5m/s)^2 = 12.5 J.
Total KE:  0 J + 12.5 J = 12.5 J
KEi = 12.5 J
KEf = 12.5 J
For my numbers KEi = KEf.
The final speed must be 5 m/s not 4 m/s.

[Momentus (OP)]

Well, here's my take on it:

Newton did it 350 years ago. I quote him in my post. Read what he says and then review your post.

[Momentus (OP)]

Let's do a quick check to see who is talking nonsense.

First and foremost we know that in an elastic collision the KEi = KEf.

This is a straw man. A very good straw man, but in no way applicable to centripetal force.
With centripetal force, as shown by Newton, there is no change in magnitude, therefore there can be no energy exchange.
Centripetal force does not change Speed.

[paul cotter]

Centripetal force is associated with circular motion. Your example is a collision. Two completely separate scenarios. I will state again that Halc's simple example disproves your false ideas, without using any maths, but you don't want to entertain it as it would undermine your erroneous conclusions.

[alancalverd]

In navigation, we talk about heading (the direction you are moving through the wind or water) and track (the direction you are moving over the ground with the wind or water).  For effect, let's replace the wind with something a bit denser.

A bug, mass 0.1 gram, is flying from west to east at 1 m/s (heading and track090) when he is hit by a 10 gram bullet travelling south to north (heading and track000) at 1000 m/s.

Using simple vector addition you can calculate the resulting velocity of the bullet with the squished bug. It's  pretty close to 999.99 m/s track 000.001, so yes, the bug is still heading 090 at 1 m/s but is unlikely to reach his original destination.

[Momentus (OP)]

Centripetal force is associated with circular motion.

In the passage from Newton's Principia,

by a single but large impulse the centripetal force acts, and brings about that the body deflects from the line Bc and goes along in the line BC

The diagram shows a blue ball traveling at a velocity of A-C, which is struck by a red ball traveling at a velocity of B-C.
The Blue ball is deflected with a resultant velocity C-D,

which I have quoted for you he shows how to derive centripetal force. If you were to read it you would see that he uses an impulse to change the direction of a moving mass. This forms a polygon, as per the example.

Newton Centripetal 3.png

You refer to collision as if it were some special force, with strange properties. A collision gives an impulsive force.

You refer to Halc?s ?experiment? as conclusive proof. He has not performed any experiments.
If you exert a very large perpendicular force to a slow-moving mass the momentum vector will be turned through 90 degrees by the impact, which will use only a fraction of the momentum of the large perpendicular force. The remainder of the momentum will then act in the direction of travel and will no longer be a perpendicular force.
When Halc does perform the experiment I suggest he exerts the force in increments, starting with a small force and building up to his golf club swinging maximum.

[Bored chemist]

Well, here's my take on it:

Newton did it 350 years ago. I quote him in my post. Read what he says and then review your post.

Unlike you, Newton understood that motion in a curve is not the same as motion in a straight line.
So it's not me who needs to review my position.

[Origin]

This is a straw man.

I looked but I can't find this strawman you are talking about.  The example you gave was about an elastic collision in which the KE is the same before the collision as after the collision.  I calculated the KE before and after the collision based on your numbers and my numbers, so where is the strawman?

Are you seriously trying to say in your example that the conservation of energy does not hold??  Does that seem even remotely possible?
 
I suppose calling a collision a centripetal force is a strawman, but that is your strawman not mine.

[paul cotter]

I was wondering about the "strawman" too and I could not see where. I think he has lost the plot totally. He certainly needs to learn some basic mechanics.

[Origin]

In the passage from Newton's Principia,

You apparently fail to understand that in a centripetal force, the force is continuously orthogonal to the movement of the body.  A momentary impulse is not what Newton is talking about  This misunderstanding is resulting in you tossing out most of Newtonian mechanics to try and protect this wrong notion.

If you are really interested in physics, you could take an introductory course in physics at a local community college (probably for free) and learn what is really going on.

Again I would like you to ponder why people who have actually been educated in physics are all telling you that you are wrong.  Do you think that no one noticed this error for 400 years except you?  Does that make sense to you?

[Origin]

You refer to collision as if it were some special force, with strange properties.

You aren't say the conservation of energy is a strange property, are you?

The only strange property I have seen in your example, is the one where you think the speed of the blue ball in the x direction decelerates for no reason.  This of course leads to the even stranger property which is the violation of the conservation of energy, which apparently is of no concern to you.

[Halc]

You refer to Halc?s ?experiment? as conclusive proof. He has not performed any experiments.

Proof? Hardly. But I did do it.  Looked a lot like your setup, but the impacts were more random.
It was done in the dark with silver balls and a strobe light reflecting onto photo-sensitive paper, leaving a series of black dots each time the strobe went off.
Afterwards, speed and direction were measured by connecting the dots and noting their separation. In each case, the momentum and energy was conserved (within the precision of the experiment, which wasn't very high since it wasn't done in a vacuum and in absence of friction.

Your asserted interactions do not conserve energy. That would mean that warm water would cool to below freezing in under a second given how much energy is lost in your single example collision. Molecules collide often in water, so if on average a third of the energy is lost with each collision (as it was in your example), then the water would cool in far less than a second.

if you can, and answer the very simple question.
Perpendicular force does not change the magnitude component of velocity. it changes the direction and only the direction.

This is true, and Newton would agree.  I agree that some of the posters do not agree with this.

Teach me O guru of science

OK.
Your force is not being applied perpendicular to the motion of the body in question. This has been repeatedly pointed out, and repeatedly ignored. So the conclusion that the speed doesn't change is false since it is based on a false assumption.

The finite force is applied over a nonzero period of time, albeit a short one. Else there would be no momentum exchange since momentum transfer is force*time.
Sure, the force is initially tangential to the motion, but as the path curves and the force peaks, the curvature brings the trajectory halfway between the inbound trajectory and the outbound one, about an average angle of 81^o or so. Hence the force accelerates the blue ball since it is always (at any nonzero duration of time) applied partially in the direction of motion.
None of this is true in centripetal acceleration where the force is perpendicular to the motion (in at least the frame of the center of rotation) the entire time. In that frame (and not in any other) does the 'orbiting' object not change speed.

The alternative (that Momentus seems to push) is that the force is applied only to a horizontal-trajectory blue ball, and only once this force concludes, does the ball begin to accelerate downward.  Both the force not causing any initial acceleration, and the later acceleration without a force being applied, are total violations of the laws of motion.

[Origin]

Your force is not being applied perpendicular to the motion of the body in question.

Could you expound on this point please.  I am not sure I understand what you are saying here.

[paul cotter]

Halc, I find myself in disagreement with your good self regarding the effects of perpendicular force( shock! horror! ). Suppose I am on a train travelling at 100km/h and I am looking out the window holding a handgun pointed perpendicular to the train, which is travelling in a straight line. The bullet in the breech is obviously travelling at 100km/h and I now pull the trigger and the bullet flies off at 700m/s. The bullet continues it's travel in the direction of the train at 100km/h but now has a speed of 2520km/h. Similar to your train example. I am sure I am misinterpreting some aspect of your argument.