Recent content by jbriggs444

Experiment shows that an accelerating clock continues to keep accurate time. This is the "clock hypothesis". It is tested by measuring the lifetime of particles traversing an accelerator ring at high speeds and correspondingly high accelerations. This is the speed of the Earth relative to a...

And not just regardless of the speed of the source. Regardless of the speed of the observer doing the speed measurement. No matter how fast you go, a pulse of light behind you will be measured to overtake and pass by you at the speed of light. No matter how fast you go, a pulse of light ahead...

It is difficult to get a prop-driven airplane to exceed the speed of sound, yes. But a centrifugal fan should be able to produce a supersonic outflow.

Yes, of course. With a little bit of time to ponder, I have a different way of explaining this. "Why was there not a directional flow of air directly into the intake of the fan?" Because we did not set one up, of course. Out of all the possible configurations of air feeding into a fan, we...

It feels like there must be a deeper reason for this. In principle, the laws of physics are symmetric and time reversible. If the input to a fan is omnidirectional, there is no reason in naive principle why the output of a fan could not also be omnidirectional. But in fact the output is...

Yes. It is sometimes helpful to consider what happens when one takes the scenario to extremes. Suppose that we have this same 5 pound ball. But instead of travelling at 1000 miles per hour, it is travelling at one mile per hour. It is being pushed three inches into the steel plate by a...

You have had opinions offered both ways. Both opinions are accurate. It depends on the details. Primarily on the duration of the collision. Or, almost equivalently, on the depth of penetration. Say that you have this 5 pound steel ball impacting a steel plate at 1000 mph. That is a bit more...

Yes, I agree with that. Prior to correcting it, I had written about points 1 and 2. I meant to refer to points 1 and 3. In both drawings A and B, points 1 and 3 are level with the top of the hook in the J. In drawing C, points 1 and 3 are further down at the level where the water is free to...

Agreed. Agreed. What increases compared to what? What specific point are you claiming does not change in pressure compared to the same point with the bubble moved? I note that points 1 and 3 moved when you changed from drawings A and B to drawing C. ##\rho g h## gives the pressure...

I have that T-shirt.

*sigh*. Now I will need to watch the video to see what it is actually claiming... Having watched the beginning of the video, I see that your original post described a transition from bubble at the top to bubble at the bottom. The video describes a transition from bubble at bottom to bubble at...

Right The second part here is correct. That means that the fluid pressure at the air-water interface is sure to be one atmosphere. The pressures elsewhere in the fluid are not sure to be the same as this. You may have to work those pressures out using the ##\rho g h## formula. Pay attention to...

Yes. Have you considered applying Boyle's law?

Why should it? Are there any specific confounding concerns that you have in mind?

Given a set of all sets, one can define the set of all sets not containing themselves. Then you ask yourself, does this set contain itself. That is Russell's paradox. In ZF set theory, one avoids the paradox by replacing the axiom of unbounded comprehension: "Given a predicate (a true/false...