12:00 AM
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Why don't we ever see an astronaut in a vacuum with a balloon? A balloon weighs so little, and so it wouldn't cost much to bring one into orbit, or even to the moon. They brought a feather and hammer to the Moon and dropped them together to show the absence of air resistance. They brought a golf ...

1 hour later…
1:08 AM
1

In section $9.5$ of Weinberg's Lectures on Quantum Mechanics, he uses an example to explain the clasification of constraints. The Lagrangian for a non-relativistic particle that is constrained to remain on a surface described by $$f(\vec x)=0\tag{1}$$ can be taken as $$L=\frac 12 m \dot{\vec x}^2... 9 hours later… 10:23 AM 2 The recent publication in Phys.Rev.Lett. 126, 141801 Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm says that A fast pulsed-kicker magnet deflects the muon bunch into a 9-cm-diameter storage aperture, resulting in \approx 5000 stored muons per fill. Considering that th... 6 hours later… 3:55 PM 5 First I want to say that I am a layperson, so I want intuitive answers. So all the 3 fundamental forces in nature has a carrier particle except gravity. So we have hypothesized the existence of graviton. But I want to know that how does the concept of graviton relates to the concepts of general ... 2 Is the probabilistic behaviour of quantum mechanics theory a direct consequence of the particle-wave duality ? Or is probabilistic behaviour an additive, independent feature (with respect to particle-wave duality) , of quantum mechanics. To reformulate in another way : if we assume that a particl... 2 hours later… 6:15 PM 2 I'm trying to solve the following function:$$ R_c(x) = 100(x_2 − x_1^2)^2 + (1 − x_1)^2  I need to find values of $x_1$ and $x_2$ as the value of $R_c$ changes. For example one solution to $R_c$ is 0, so $R_c=0=100(x_2 − x_1^2)^2 + (1 − x_1)^2$ and then I need to solve for $x_2$ and $x_1$. A...

1 hour later…
7:21 PM
5

This is a relatively difficult question I found on a past exam (12% got it right): Two spacecraft travel in opposite directions, with spacecraft Ajax travelling at a speed of 0.5c and spacecraft Hector travelling at a speed of 0.4c. Both are travelling relative to the inertial frame of the galax...

2 hours later…
8:51 PM
2

Also dont understand this question i found on a past exam paper (31% got it correct): A robot is heading radially towards the surface of a planet in the Hoth system at a constant speed of 0.85c. Observers on the surface of the planet observe it at a time when it is a distance x above the surface ...