Split Thread The validity of classical physics (split from: DWFTTW)

[spacediver]

Humber, you should apply for the million dollar challenge.

If you can convincingly demonstrate that two objects that pass by each other have zero KE at the moment they are passing by, you will have succeeded in demonstrating the paranormal.

 

[H'ethetheth]

That is a simplified equation. Yes.
But what I mean? What is the significance? Yes, A- B =0.

It's significance is that if you do regard velocity as vectors, then equal velocity means equal magnitude and equal direction. If we define KE as proportional to the dot product of the velocity vector and itself, it will not be zero for cars passing eachother by at the same speed.

Let's say you are on an object in space. You get out your saw and cut it in half. Being space, it will stay there. That is the nature of zero KE objects.
The argument is not supportable if one is spinning, because only the notional centre of mass can be said to have the same velocity. All other degrees of freedom do not.

You lost me threre.

You should.

I have.

 

[humber]

No, the "incredibly stupid" thing he was referring to was this:

Ditto

How can two cars with the same velocity pass one another? They're not moving relative to one another, by definition. You're going out of your way to misunderstand and mangle things, and it's really getting old.

Exactly. You tell me why zero KE has any significance, and not just a trivial limiting case, taken so you can repeat it like a parrot.

 

[humber]

It's significance is that if you do regard velocity as vectors, then equal velocity means equal magnitude and equal direction. If we define KE as proportional to the dot product of the velocity vector and itself, it will not be zero for cars passing eachother by at the same speed.

Now that you have cleared that up with yourself, perhaps you would like to explain the significance of the equation you posted.

Perhaps you have noticed that the general use of vectors in this thread is the scalar "speed" with "to the left" added.

You lost me threre.

Why? Please see above.

I have.

One dimensional pedantry.

 

[humber]

If the cars pass each other they have a non-zero relative velocity. If they have a non-zero relative velocity they can't both have zero velocity in any frame, therefore at least one of them has non-zero KE in any frame.

Partly correct. However, it is then clear that zero KE exists only for objects following the same path. There can be no relative motion between them at all. They are effectively one mass. Any relative motion at all forces them from zero KE.

"Something as zero KE w.r.t to itself, or some other thing indistinguishable from it."
The basis of a sound system of science and engineering. Boundless applications.

I think there's a problem with the phrase "less delusional".... it's like "less completely wrong".

Not at all. Think again, or at least once.

 

[humber]

Humber, you should apply for the million dollar challenge.

If you can convincingly demonstrate that two objects that pass by each other have zero KE at the moment they are passing by, you will have succeeded in demonstrating the paranormal.

Wait a minute there SD, "zero KE' is your idea not mine.

Over what time period do you determine the object's velocities.?

Simple. V1 + (-V2) = 0 . So you (all) tell me.

 

[Christian Klippel]

Simple. V1 + (-V2) = 0

And another blatant stupidity from our "i have superior knowledge" guy.

Just a hint: There is no such thing as negative velocity in the way you apply it here.

 

[humber]

And another blatant stupidity from our "i have superior knowledge" guy.

Just a hint: There is no such thing as negative velocity in the way you apply it here.

tsk tsk.

 

[RossFW]

Greg? Greg!!! Don't run away Greg! We need you!!!!

I think you may be getting a taste of what we are up against!!!!!

 

[RossFW]

The effect of something slower, but moving backwards, is a result of our vision and subsequent processing. It is no more valid to use your eyes to determine relative velocities, than it is to say that "things get smaller" with distance. In fact, you are seeing the object subtend a smaller angle.

That will be a relief when it only "Apparently" hits you!!

 

[humber]

That will be a relief when it only "Apparently" hits you!!

How so? One is slower than the other. The appearance of "backward motion" is an illusion.
This also goes for vehicles that brake. Sometimes drivers don't realise that, and make the mistake you just did.
A car actually going backwards, i.e. in the other direction, is quite different.

 

[GregLondon]

No, the yo-yo will not work.

Uh... what?

do you mean the yoyo won't go faster than the string pulling it?

If so, I don't know what to tell you. I was talking about the whole DDFTTW idea with a friend and he was having a hard time understanding it with just verbal explanations, so we built a big yoyo out of paper plates for wheels, a soda can for an axle, string, and tape. when you put it on the ground and pull the string so that it wraps around the bottom of the soda can, the yoyo catches up with your hand.

the yoyo is little more than a block and tackle, and if you get that a block and tackle can change the amount of rope you pull by changing the amount of force transferred, then i'm not sure how you can say the yoyo won't work. Or I don't understand what you mean by "won't work".

 

[humber]

Uh... what?

do you mean the yoyo won't go faster than the string pulling it?

No, it will go faster. That is true, but then you are simply applying enough force/power for it to do so. Why stop there? A gain of 'n'
There are many things that can be said to travel "faster" in this way.

If so, I don't know what to tell you. I was talking about the whole DDFTTW idea with a friend and he was having a hard time understanding it with just verbal explanations, so we built a big yoyo out of paper plates for wheels, a soda can for an axle, string, and tape. when you put it on the ground and pull the string so that it wraps around the bottom of the soda can, the yoyo catches up with your hand.

Yes, but id you don't manipulate the acceleration to exploit the difference between rolling and static friction, it may slide, rather than rotate.
Generally,though, it is as you say.
Yo-yo's work like that, not just as you have described, but as the original toy. How else? That characteristic is what makes them yo-yo like.

the yoyo is little more than a block and tackle, and if you get that a block and tackle can change the amount of rope you pull by changing the amount of force transferred, then i'm not sure how you can say the yoyo won't work. Or I don't understand what you mean by "won't work".

The maximum velocity of a chute-driven device, will not only be determined by the force or velocity available from the chute, but also the power available from the chute. The yoyo's "gain" is therefore not of explicit use. Many other vehicles without it, will achieve the same velocity.

The yo-yo is a set of concentric wheels. The "block and tackle" is perhaps analogous.

 

[RossFW]

How so? One is slower than the other. The appearance of "backward motion" is an illusion.
This also goes for vehicles that brake. Sometimes drivers don't realise that, and make the mistake you just did.
A car actually going backwards, i.e. in the other direction, is quite different.

I see. And if we, say, wanted to know how much damage the collision would cause. Might there be some way of calculating it? Might we look at the difference in the speed (WRT the ground, of course. There is NO OTHER reference!!) between the vehicles? Might we call it, oh I don't know, closing speed?

Someone called Newton called it "Relative velocity", but what would he know!

And how would we calculate the impact? Might the energy involved have something to do with it? Maybe someone, sometime thought of a formula for it?

KE=1/2M*V^2 rings a bell, where V is that thing Newton mislabled...

 

[RossFW]

Or I don't understand what you mean by

Get used to it, Greg!

 

[GregLondon]

The maximum velocity of a chute-driven device, will not only be determined by the force or velocity available from the chute, but also the power available from the chute.

Are you talking about efficiency?

If so, it still works. Say you have a 10 mph wind. but the parachute is only 60% efficient, so it moves at 6 mph. So, you have a string moving at 6 mph, wrapped around the axle of a yoyo, and you want the yoyo to move faster than 10 mph. All you need to do is choose the diameter of the axle versus the diameter of the wheel touchign the ground so that the "gear ratio" is better than 10/6.

By changing the diameter of the axle, you can select whatever gear ratio you want, and a string moving at 6 mph wrapped around the axle can make the yoyo move at 10 mph or faster, which is faster than the wind.

The fact that the parachute isn't 100% efficient just means you'll have less power to work with, but by choosing the gear ratio, or the "block and tackle" ratio, you can still get that power to move you faster than the wind. The trade off would be that the force to move the vehicle becomes smaller and smaller, meaning that your accelerstion will be smaller. So, you slowly accelerate, but its still acceleration, and eventually you reach a state faster than the wind.

 

[Tunny]

Wait a minute there SD, "zero KE' is your idea not mine.

No, the notion of "two passing cars" having zero KE was your idea:

If two cars are at the same velocity, they have the zero KE w.r.t each other? So two passing cars will at some point have zero KE. For how long?

Tunny

 

[humber]

I see. And if we, say, wanted to know how much damage the collision would cause. Might there be some way of calculating it? Might we look at the difference in the speed (WRT the ground, of course. There is NO OTHER reference!!) between the vehicles? Might we call it, oh I don't know, closing speed?

The damage would be the result of the dissipation of the sum of the vehicle's KE. Yes, relative to the ground, because the contact of the wheels with the ground, is how the energy produced by the engine finds its return to ground. ""On the way" the mass of the car stores some of that energy as KE, the direct result of acceleration. Once at a fixed speed, that KE remains constant. The engine's power overcomes the forces of drag, so that the vehicle remains at that speed. That is, so it does not decelerate.[/]
The closing speed is indeed the difference between the cars speeds, but also between each car's speed w.r.t the ground. That is a common factor, while not explicit in the calculation of the relative velocities, is nevertheless implied for ground travel.

Someone called Newton called it "Relative velocity", but what would he know!

Well, Newton spent more time on alchemy (writing 2 million words) and trying to turn base metals to gold, than he did on motion, so I suppose by modern standards, that makes him an idiot. But of course not.
Perhaps he took it as read, that his readers would understand that gravity makes the type of isolated relative motion you describe, quite impossible. That objects don't simply arrive at 'V' but must be accelerated to get there.

And how would we calculate the impact? Might the energy involved have something to do with it? Maybe someone, sometime thought of a formula for it?

As above, RossFW. Of course, in the real world, some of the KE will be transferred to the ground or fixed objects, and as heat through friction. Do you think that an accident where both cars fall of a bridge, may be somehow be different from the same at sea level? Gravitational potential energy?
But don't forget to include that we are all traveling around the Sun!. That is also a common factor, but one that essentially drops out of the equation.

KE=1/2M*V^2 rings a bell, where V is that thing Newton mislabled...

Equations are "application dependent", RossFW. They assume that you also recognize the nature of the system to which they apply.

 

[jjcote]

The damage would be the result of the dissipation of the sum of the vehicle's KE. Yes, relative to the ground, because the contact of the wheels with the ground, is how the energy produced by the engine finds its return to ground.

Fascinating. So, how do airplanes work? How does their energy return to ground, since they aren't touching it? And what about airplanes that are taxiing, touching the ground, but still moved by their propellers?

 

[humber]

Are you talking about efficiency?

Not specifically, no.

If so, it still works. Say you have a 10 mph wind. but the parachute is only 60% efficient,..

That is not efficiency, but OK

...so it moves at 6 mph. So, you have a string moving at 6 mph, wrapped around the axle of a yoyo, and you want the yoyo to move faster than 10 mph. All you need to do is choose the diameter of the axle versus the diameter of the wheel touchign the ground so that the "gear ratio" is better than 10/6.
By changing the diameter of the axle, you can select whatever gear ratio you want, and a string moving at 6 mph wrapped around the axle can make the yoyo move at 10 mph or faster, which is faster than the wind.

Efficiency is important, but not directly relevant to the point. The available power is determined by the chute, not the load. The load is power demand. Once demand meets available, acceleration stops, and a steady velocity maintained. What you do in between, will not change that final velocity. The demand in this case is the drag load of the vehicle. To go faster, reduce that, or get a more powerful chute.
There are two components to the demand. Energy to supply that being stored in the mass of the load as KE, the direct result of acceleration, and the dissipative load of drag. It is the latter that determines final velocity, not the acceleration to that velocity.
This is the case with the car. The maximum speed is determined by the engine's power; it's capacity to do work against a load. Lower gears may give better acceleration at lower speeds, but that does not change that final result. So, geared carts or yo-yo's may gain in that respect, because they can exploitany power that is available and so accelerate faster, but the terminal speed is fixed by the same means as any other chute driven vehicle; by the available power.

The fact that the parachute isn't 100% efficient...

That means they won't travel at windspeed.

....just means you'll have less power to work with, but by choosing the gear ratio, or the "block and tackle" ratio, you can still get that power to move you faster than the wind. The trade off would be that the force to move the vehicle becomes smaller and smaller, meaning that your accelerstion will be smaller. So, you slowly accelerate, but its still acceleration, and eventually you reach a state faster than the wind.

No. The chute can only deliver a certain amount of power ( force x velocity) and that is quite dependent on its velocity relative to the wind. As you are dragged by the chute, your demand will increase as a result of drag.
To a first approximation, the chute's force is linearly related to its velocity w.r.t. wind, and that falls as its gains velocity, (so reducing its velocity w.r.t the wind) whereas the drag, the demandedforce, is the square of that velocity and so increases as you gain velocity, but at a faster rate. You will lose the battle well before windspeed.

(If the chute's force is related to the differential with the wind, and power is force x velocity, you should see intuitively, that a peak in the power will occur somewhere between zero and windspeed. That velocity, and its related power are design dependent.)