Physics Answers - Part 3

 Physics Questions from Quora that I answered.

Can we perfectly predict the position of a planet in the solar system using Newtonian mechanics only?

All measurements in science carry with them a degree of error. In addition every scientific model has built in it several assumptions that do well to approximate reality but aren’t reality in and of themselves.

If you assume the ideal yes one can obtain a very accurate determination for planetary position especially in a two body problem. Three body systems are far more complex.

The fly in the ointment here with this question is the word ‘perfectly’. Its etymology forces us to reduce all uncertainty to zero. This is impossible as even in such an ideal system (with no margin of error) we cannot ignore Quantum Mechanical concerns (small as they are) nor do we have the luxury of freezing time to peg the position as exactly X. The world is an inherent system of flux and change.

Do all planets revolve around the sun with the same speed?

No they don’t. The closer a planet is to the sun the greater the pull of gravity on that planet. To maintain an orbit the planet therefore is forced to move at a higher velocity with decreasing orbital radius. The higher velocity provides for a greater inertia in motion (or linear momentum) to resist the inward gravitational pull.

The equation v = (GM/r)^0.5 describes the relationship where G = Universal Gravitation Constant. M =mass of the sun (kg) and r is the radius of orbit. v = orbital speed (or velocity magnitude).

As r decreases v increases. Notice as well that the value of v is independent of the planet’s mass.

The above equation can be derived by equating Newton’s Law of Universal Gravitation with the expression for the Net Centripetal Force and is related to Kepler’s Third Law of Motion.

Is Quantum physics physicists a good field to enter nanotechnology from?

Nanotechnology is one of those multi-disciplinary areas that draws in people from a variety of educational and experiential backgrounds. This makes sense as it has applications in electronics, medicine, materials, fluid mechanics, the military and environmental sciences to name but a few offshoots. Many engineering schools now have a specific department geared solely to nanotechnology. Nanotechnology Engineering

It has been an emerging discipline for some time and will likely play an important role in both the pure and applied sciences for the remainder of the 21st century.

Physicists with a strong background in quantum mechanics will always enjoy an advantage in nanotechnology as many of the effects that make the technologies possible rely heavily on quantum considerations viz. tunneling, wave-particle duality and various interactions at the matter-energy interface.

However there appears to be a demand as well for those with strong skill sets elsewhere. A molecular biology background and proficiency in computer coding cannot hurt.

What is the most important element in all of physics?

Hydrogen. It is the most abundant element in the universe and is the starting point for virtually every fusion system. It is through fusion that almost all of the other elements have been produced.