To budding astronomers.
A difference between true velocity and proper velocity. Proper velocity (proper motion) is the motion of a star apparent to the center-of-mass of the solar system. That is, how fast any object (a star) is moving wrt the sun’s position. (in terms of its center-of-mass)
So if a star is close to sun, its true velocity might be as much as it is, but proper velocity can be larger. Proper velocities are often larger when stars are closer, an useful fact in Astronomy.
(How proper velocity is eg useful in Astronomy, should be a good essay type question in Indian University exams, in the course of astronomy, but rather its more useful to remove essay type questions from Exams of University and such essay should be written by students as blogs, and the best blogs can be rewarded, Change should be brought to our education system by innovative thinking and not just by lecturing on outdated spiritual discourses) More…
2. Last year in a text book in Indian High School curriculum, I spotted and corrected with my students, the following:
Myth; there are only 3 quarks that have been detected or FOUND/confirmed so far, in nature.
Its based on a knowledge that was true more than 3 decades ago. All quarks, 6 of them, have been confirmed as hypothesized, the last of them was confirmed 2 decades ago. So there is really no reason why these facts should have been omitted from the text books that are updated every few years as such. Who are our experts?
3. During my freelance research, I have pointed out the following fact within last 3 or 2 years. A recurring myth in very advance texts of physics, concurrently followed in major and wide number of universities around the world, some of the finest texts in the field of particle physics and widely believed to be excellent, which they are nonetheless.
Myth; (particle life time and range of forces) A (force carrier) particle is long range if its mass is zero. Lifetime is the uncertainty that gives rise to an energy which is equivalenced through Einstein’s mass-energy relation and mass being zero, we have an infinite range as range is inversely proportional.
Fact; This is murky waters. Its a manipulation of sorts. Experimentally life times are quite arbitrary, while mass is supposedly fixed. Neutrino has a mean-life from 15 seconds to 10 billion seconds in order of magnitude .. I have hypothesized that’s possible, because it has such a high energy, and given it can’t lose this energy via any possible processes, it must live that long. More…
Result; now that photons are mass-less, their energy, momentum, speed, etc are no more variables, in the sense of arbitrariness. They are constants, taking only a few values, but constant in a given situation. But other particles have these properties; arbitrary. So electrons energy and momentum are not fixed, but arbitrary.
But as long as we are considering only elementary particles (that is, we are in a Quantum Zone) eg, electrons, protons, photons, and not nutmegs, soccer balls and airplanes and satellites there is another quantity that is of important consequence that is constant. Spin; whether a mass-less particle or not, spin has the same magnitude for them. that is spin is same for photon, its always 1. Spin for an electron is always 1/2. Spin for proton is always 1/2. Its for this reason photon is called a Boson**. Any thing with spin, 0, 1, 2, etc will be a Boson. Anything with spin 1/2, 3/2 etc will be called Fermion. More…
A photon has no mass but energy and it has speed and it has momentum although it does not have mass. Thats impossible in Classical Mechanics. Because Classical Mechanics associates with every mass; momentum and kinetic and potential energy. All those would be zero if mass were to be zero.
Also the speed of the photon is constant while its energy and momentum are changing. This is unimaginable in classical mechanics. In CM first momentum can’t be defined from mass and speed if mass is zero, then while speed is not changing how is momentum changing? So both variables speed and mass fail to define a momentum for the photon, and not just the failure to have a mass. How then momentum is defined for this particle? Its not defined as long as photon is just a particle. Thats impossible. More…
This post has 40 interesting problems in elementary mechanics from IE Irodov, Problems in general physics that I solved in last couple weeks. Note that another 30 problems which has been solved will be uploaded after they are scanned, shortly. More…
Here is a problem on mechanics.
Problem; Two particles move in a uniform gravitational field with an acceleration g. AT the initial moment the particles were located at one point and moved with velocities v1=3.0 m/s and v2=4.0 m/s horizontally in opposite directions. Find the distance between the particles at the moment when their velocity vectors become mutually perpendicular.
Here is my ans. (Got to fig. it out in a concise way after scribbling through pages unsuccessfully. )
An interesting problem in mechanics