Speed Definition and 999 Threads

Just saw this Youtube Short by Veritasium. The idea is that two identical chain ladders are dropped at the same time. One hits a table shortly after release, while the other continues to free fall. Curiously, after the bottom of the first ladder hits the table, the remainder still in free fall...

In the illustration below, a laser beam is emitted, and the time recorded, from the rear of a frame which is 150,000 km long and is moving at velocity 0.5 c to the right. When the beam reaches a half silvered mirror at the front of the frame, the frame being shown as a rectangle and using...

Is my understanding correct that if we have a moving vehicle moving to the right at speed v, as above, with a light source in center going in both directions, that (upon emitting the light at time T), a detector at D1 & D2 would both detect light reaching it at T2? (even though in the time it...

I used the work-energy equation to solve this problem.Only the parallel component of force acts to accelerate the biker and increases K.E., so only the parallel component and frictional force does work on the biker. therefore, Net work done on a system = change in K.E $$(F_I{_I} + F_F) d...

I once read (though I don’t remember where) that in the same way that you talk about a dimensionless ratio between Y and X in ordinary space, you can conceive of c as a dimensionless ratio between T and X in spacetime. Do you know where I can find a reliable treatment of that idea? As...

In MOND should two small masses placed at a great distance orbit faster than in Newtonian dynamics? Would it be theoretically possible to do this experiment in the solar system, or would the presence of the sun and earth be a problem?

This is much like the "grain of sand" at near speed of light hiting Earth, but now targeting Jupiter with a needle! What if... Any way, which is the correct way to analyze this kind of scenarios? For example, I think than being the speed of the needle near c, is nonsense to think about the...

I perfectly understand that we cannot, as of our current methods, determine the one-way speed of light - I was, however, wondering if we could determine a relative speed using electrical transmission. the basis of which would be sending a laser light across a field into a sensor, starting a...

This is probably a dumb question. I'm not a physicist and took basic physics a very long time ago. If an object was in deep space, a long way away from gravitational fields and was subjected to a constant 1g acceleration in a straight line what prevents it from eventually exceeding light speed...

Relating to Stratus' thread in this forum, I'm trying to figure out initial velocity of a jump in zero g. Lets start in 1g. In one g, a person might be able to jump 1m. From this, using : v^2 = u^2 - 2as, we can calc his initial u as 4.45m/s. Is it a safe assumption that, were an astronaut to...

I've found the inductance and capacitance per unit length in a long coaxial cable. I even clearly see that if I multiply the two, I can get the speed of light. How do I begin to find the current wave and its speed though?

I've been bothered lately with an excessive number of freezes and dropouts when trying to conduct meetings on Zoom. As many as 10 freezes with 5 dropouts in 15 minutes. I installed a tool to monitor my connection from my PC. In 4 hours, it gathered the following stats. General stats...

Since the radius is "very far", I cannot find the total mechanical energy by using the gravitational potential energy formula and find the kinetic energy at impact. I can't think of any other way to find final velocity without knowing the radius.

Hi, I have a task where i have to calculate the speed of which the air is flowing out of a drones propeller fan. This is all i have been given: The mass of the drone m = 0.42kg, There are four propellers the lenght of each blade d = 0.21m, the air density is 1.3 kg/m3 and g=10 m/s^2y. And the...

When I attempted this problem, I came up with two different solutions and answers, and both seem correct to me. However, the answer obtained by the first method is correct according to the book. The methods I used are as in screenshots below. Isn't the problem statement ambiguous, or maybe I...

V = ? m/s V = D/T V = Square root (6.67 * 10^-11)(m)/r

My school's group project is to design a powered model flying wing that can fly for as long as possible. To make it stable in the longitudinal direction, we either have to use a swept wing design or an airfoil with reflex (like BR1). We are forced to use wing sweep because the airfoil with...

Quote from NASA: My understanding of dark energy is based on NASA's report: https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy; were NASA state as follows: "It turns out that roughly 68% of the universe is dark energy. Dark matter makes up about 27%. The rest - everything on...

Suppose we have an expanding sphere. That means that the surface ##4 \pi r^{2}## is getting bigger and bigger. For example, suppose the area expansion rate is ##b \, r##. Does this limit the speed at which a point can move on the surface?

As it is clear from the formula for r.m.s speed ,it is only dependent of temperture for a particular gas,I think the answer should be "No change happens".But I wonder whether there is more insight to this.And is my assumption true?

Based on the little I know ion thrusters seem extremely impractical on earth, even because speeds over 20,000-30,000+km/h will result in immense friction and fire, so why not cut the high speed somehow and increase thrust which is abysmall? For example: the ions passing through a medium?? Wider...

11 rpm equals 1.15 rad/ sec not sure how this helps contribute to the question but I solved for it just in case

I want to make a few of these if it will not cost a lot.

Molecular speed of gas is generally $$v=\sqrt{\frac{3RT}{M}},$$where R is gas constant and M is molecular mass. Can we use this formula for the air as well, when the air is a mixture of different gasses?

TL;DR Summary: Have a university project where we are calculating the speed of the arm at the end. I need some help on where to start on the calculations. We have tried to determine instantaneous center of rotation for the device. We want to find the linear velocioty of point B. There is a...

I drive car only at country roads allways at speeds 100-120km/h, no city and no idle time-heating engine etc. Why computer allways show very low average speed , 40-48km/h?I allways have feeling that this speed is too low because I allways drive way faster then this. Indeed all my friends have...

Wasn't sure where to drop this thread, so here it is! I've searched the internet and this forum, perhaps I don't have the correct keywords, but I haven't been able to find anything that discusses this topic. I'm interested to know about your individual experience of learning. I'd like to think...

hello Einstein assumed the invariance of the speed of light as an hyphotesis, while I was told that : "The speed of light need not have been postulated as an invariant." in other words the invariance of the speed of light could have been proven even regardless of the special relativity is it...

What is the difference between the GTR vacuum and the vacuum of quantum theory? What is the speed of light in the vacuums, specifically what can be predicted and what must be measured?

hello everyone According to Einstein's second principle of relativity: "The principle of the constancy of the speed of light: The speed of light in free space has the same value c in all inertial reference frames" Does free space mean vacuum? Is this principle not valid in the air and the...

I substituted 0 for vi, as the rocket is initially stopped. I am looking for Vf. So: Vf^2=0+2asΔs Vf^2=2asΔs I then substituted a=Fthrust/m So: Vf^2=2(Fthrust/m)Δs Δs at any given moment equals h so I substituted h for Δs. Then took the square root of both sides. Vf=sqrt(2h(Fthrust/m)) It...

Since the period is 0.025s, I think the frequency is 1/0.025s = 40 Hz. I don't know how can I proceed solving the problem from here. I'm assuming I will have to try to find the velocity and wavelength, but idk how.

I don't know if I wrote it correctly

<unacceptable reference deleted> As our universe is expanding, that is, our vacuum is becoming more and more sparse, I believe it is possible that some key characterics of our vacuum is also variable.

hello everyone I read this text in physics book: "Another example is the so-called Cerenkov radiation, which consists of light waves emitted by charged particles that move through a medium with a speed greater than the phase speed of light in that medium. The blue glow of the water that often...

Does the speed of light imply that in its property as a wave it encompasses the entire known electromagnetic spectrum?

Hello, I have a problem with the postulate of the invariance of the speed of light. When we move away from a light source it is redshift, it is the sign that the relative velocity between us and the light source has changed. If a stationary observer observes the phenomenon, he will measure that...

I am new to this forum and in line with its rules I am trying not to repeat a question already asked. I find that Jeremyfiennes original question I.e Experimental evidence for effective mass increasing with speed” is the question I want to ask but I am not satisfied with the answers given so...

The speed of a wave in simple harmonic motion on a string is $$v= \sqrt{\frac{F}{\mu}}$$ where v= the horizontal velocity of the wave on a string. Is the F the horizontal force or the resultant force (combination of Fy and Fx)?

Hello, I am talking to a Quantum Mechanics Physicist friend who is having a hard time accepting some of the Cosmology theories and numbers and I want to be sure that my numbers were correct. 1. Firstly, what is the recession speed, today, of the matter which created the CMBR? I told him that...

Imagine a plane 1 light minute across. Now imagine 1 person on either and of that plane. Between them, is a thin indestructible bar that is 1 light minute in length. In the center of this plane, a simple device has a wire that leads to a motion sensor on the left side of the bar. If the left...

Hello, Given a set of numbers, we can calculate their average and there are different types of averages (arithmetic, weighted, harmonic, geometric, etc.) The choice of the average depends on the situation. The average, also called mean or expectation value, is a number that can replace all the...

We can derive the constancy of the speed of light from Maxwell equations. My questions are: 1. Why it is then need to postulate it when we can obtain it from Maxwell equations? 2. It is stated in many books that gravity wave also propagates with the same speed, c. How do we conclude that? Is...

We can measure the two-way speed of light, but not, apparently, the one-way speed. Light could travel at c in every direction or c/2 in one direction and instantaneously in the other. Nature does not provide us with a way of determining the one-way speed. I can follow some of the basic...

I get it, it sounds cool. But it is a very misleading and sometimes confusing way to represent c. The speed of light is not constant. When I say that, I’m talking about the speed of LIGHT. Not c. Cherenkov radiation is a result of particles moving through some material (usually water) faster...

I watched a fermilab video claiming objects don't actually gain mass as they approach light speed. Is that true? What keeps things of mass from reaching the speed of light or beyond? I assume matter doesn't accumulate higgs-bosons while in motion?

A ship that moves at a speed very close to light, its relative mass increases and may be comparable to the mass of the planets or the sun, in this case it can change the orbit of the planets and the sun (according to the law of gravity of two bodies) Is this analysis correct?

hello everyone! Recently,i'm reading a paper about slow light,that's really a famous work published in Nature.[Light speed reduction to 17 metrespersecond in an ultracold atomicgas]. But I'm trouble with some calculation about the velocity of slow light.here are below: i try to use the...

Is there experimental evidence that confirms that the speed of individual photons in a vacuum never varies, even slightly? Thanks in advance.

There is a trivial metaphysical freedom, that emerges from the fact that people living in a world must use their own measuring devices, that are part of that world. E.g. people living in a flatland must use their own rulers to measure distance. If one half of their world is widened, they...