Question

Answer it in detail (1-2 paragraphs)

1. Define a reference frame and then an inertial reference frame. Give example of both inertial and non-inertial reference frames.

2. Explain the concept of time dilation. What is the twin paradox?

3. Explain why it is impossible for an object to travel at the speed of light (Hint: evaluate the energy of the object)

4. Discuss the importance of the photoelectric effect in the context of quantum physics.

5. What is the de Broglie wavelength? List at least one experimental evidence the matter exhibits wave characteristics.

6. State Hesisenberg's uncertainty principle.

Answer 1

1) Reference frames in general are just "black boxes" used to define your immediate environment, and reference for all kinematic quantities. For instance, you can conduct your motion experiments within a closed aircraft cab unaware of the fact that the aircraft is moving...or you can conduct your motion experiments on the ground in your laboratory.

In classical mechanics, we define an inertial reference frame as a reference frame that is moving at a constant velocity...i.e. constant speed and constant direction.

You don't need to know this right now, but in Einstein's relativity subjects, prescence of a gravitational field can disqualify a reference frame from being inertial, in the sense of his thought experiments...but let's leave that story for another day.

In classical mechanics, we get away without making that distinction of gravitational fields disqualifying an inertial reference frame, because we are willing to consider gravity to be a force just as much as a human push or pull is a force.

The reason we have the inertial vs non-inertial reference frame concept is that EVERY OBJECT of the reference frame needs to receive the proper force per unit mass in order to be accelerated. So in a sense, a non-inertial reference frame is "not as good" as an inertial reference frame.


If you were unaware that the driver of a van slammed on the gas pedal, and you were in the back, not seeing the outside world, you would *think* that somehow a mysterious gravity-like force suddenly came in to existence making you fall backward....and it isn't a force at all, since there wasn't any object actually causing you to accelerate backward. In fact, as an observer on the ground would say..you weren't accelerating backward, the van was attempting to "leave you behind" until the back wall crashed in to you.



The inertial reference frame is the truest possible reference frame. It doesn't matter how fast it is ultimately going or in which direction...all inertial reference frames work. That is the reference from which is best to measure acceleration if you want the sum of every force that is obviously a force to equal m*a.


So here on Earth...do we have access to an inertial reference frame?

No we do not. We are stuck being residents of a rotating celestial body.
But is it close? Well of course it is close. Rotating once in 23 hrs and 56 minutes...that is damn slow of a rotation.

For what it is worth...most practical situations can disreguard earth's rotation when solving motion problems. For all that matters, our solid ground is the best reference frame we've got.


All that the rotation really does to us is make gravity seem to be slightly less. That is all.

Oh...wait...there is the coriolis effect. But that is only significant for sitautions involving large distances traversed across Earth.