## Is there any law that prevents an object with mass to become massless?

I got into a discussion with my physics teacher about the speed of light and I asked What if an object with mass was to lose mass as it gained speed– would that allow for an object to eventually reach the speed of light or surpass it if possible through that thinking? My teacher didn’t … Read more

## Does relativistic mass violate the conservation laws?

When an object’s speed increases, its (relativistic) mass increases. Are new atoms created inside the object by its increased speed? or is its “gravitational charge” increased by its increased speed, without more atoms? Answer No new atoms are created. What actually is increasing is the energy of the object. And because the energy and mass … Read more

## Mass of the electron

In the classical limit, three quarters of the mass-energy of the electron come from the energy of the electromagnetic field of its charge (see Electromagnetic Mass). Intuitively one would expect that the exact formula in the quantum limit may be different, but the general concept would remain, meaning that at least some mass of the … Read more

## F=maF = ma and instantaneous force

I’m new to physics and trying to understand Newton’s second law F=ma but I don’t think I’m grasping the concept of force very well. I’ve read other questions and answers on this law and it is my understanding, for now, that F=ma is a “definition” of force based on the empirical “law” that the product … Read more

## Does the recent re-count of stars in elliptical gallaxies affect our understanding of the universal mass balance?

I’ve seen several popular reports of a new count of low-mass stars in elliptical galaxies (here’s one). Edit: Pursuant to several correct comments I’ve changed the title to agree with the actual report which is that the recount concerns elliptical galaxies—and I don’t know where I got the notion that it concerned dwarf galaxies—but I … Read more

## What does “nearly infinite mass” mean?

I am sure this is a silly question, but I was reading something that described the pre big-bang universe as having “nearly infinite mass.” How can something be “nearly” infinite? The term seems to make no sense. Answer Any natural number, no matter how large, is “infinitely far away” from infinity, i.e., there are an … Read more

## Why are particles different sizes?

Is it correct in saying that a particles size is it’s rest energy, and that particles don’t actually have size (in the way you get different size objects)? What defines what sizes a particle can be? Why do particles have discrete sizes, and there’s not a continuous spectrum of particles varying in size? I ask … Read more

## If rest mass does not change with vv then why is infinite energy required to accelerate an object to the speed of light?

I know that as the velocity increases, the mass of the object also increases so it becomes tougher and tougher to move the object which ultimately leads to a requirement of infinite energy to accelerate an object to the speed of light. But I have a doubt. As far as I know only the observable … Read more

## Why is there a density instead of mass in the Navier-Stokes Equation, if it’s analogue to Newton’s Second Law?

I read in Ian Stewart’s 17 Equations that Changed the World book that Navier-Stokes equation (I know it’s not exactly a scientific book, but still, I’d like clarification on what is wrong if it’s the case): ρ(∂v∂t+v⋅∇v)=−∇p+∇⋅T+f is an analogue of Newton’s Second Law, for fluids. Newton’s second Law states force is equal to mass … Read more

## How do we measure mass?

How do you measure mass? Weight is easy using a scale, but we can’t measure mass that way, because then mass would be different on every planet. I know there was a Veritasium video (here) on defining what, exactly, one kilogram was, but they can only define that if they know some previous measurement (i.e., … Read more