Physics Question (1 Viewer)

[siraulo23]

I need help on a number of questions (homework)

Question 1: If you are in a car moving at constant velocity, you can see that the car is moving. Does it violate the principle of relativity? Explain

Thanks in advance

 

[ilikebeeef]

In the ideal world, if you were in a car travelling at constant velocity, you wouldn't see that the car you're in is moving, but that everything around the car is.

 

[pman]

no, you have a point of reference outside the car, the car is not moving relative to you but it is moving relative to its surroundings.

(I do not disagree with Ilikebeeef)

 

[Pwnage101]

It does not violate the principle of relativity because you have reference to an external point (outside your frame of reference).

 

[siraulo23]

Thanks guys

 

[siraulo23]

More questions, plz help!

1) If im in a rocket ship travelling in deep space, and I can see nothing outside the windows, how could I tell whether or not the ship was moving with constant speed, accelerating or stationary?

2) Identify 3 different situations which we classify as inertial frames of reference

3) The principle of relativity states that we cannot do any experiment or make any observation within an inertial frame of reference to determine if we are moving with constant speed velocity or stationary.

However if we are in a plane, moving at constant velocity, we can tell we are moving by looking outside the plane.

Are these two statements in contradiction with each other? Please explain

 

[siraulo23]

anyone? xD

 

[Oobadoo]

I'll reply! Though, I should warn, I am in year 11, and so would have a pathetic knowledge of physics compared to you. I'm only answering because noone else is. Here goes!

I'll only attempt the first one; note. Well, I guess you could tell if the ship was at constant velocity or accelerating through mere observation of matter within the ship it's self. Theoretically, if you, for example, placed liquid into a container on the ship, assuming there is no gravity, and assuming this is a perfect scenario in which you managed to place the liquid into the container so as it sat at a point of complete statis; if the ship changed velocity, or accelerated, negative or positive regardless, you would observe a change in position of the liquid; it would move. Vice versa.

As I said; this is a very basic and probably laughable answer to your question. However, noone else answered so I did. There you have it. lol

 

[Slowness]

Hey,

1) This can be done through the Pendulum Experiment. There is no air resistance in deep space so if you are travelling in constant velocity, then the pendulum should stay still. If you are accelerating, pendulum should move towards back of space ship and if you are decelerating, pendulum should move forward. Everything moves at a constant velocity till a force is acted upon it. The force is the place the pendulum is tied to. It'll pull it back when you are decelerating ... hope you understand that

2) My text book states (Jacaranda Physics HSC2 pg 82) that "the principle of relativity applies only for non-accelerated steady motion; that is standing at rest or moving with a uniform velocity. this is referred to as an intertial frame of reference. SItuations that involve acceleration are called non-inertial frames of reference".

3) This is the exact next point in the text book same page 82. I don't think you would be able to. From your frame of reference, you are stationary (since you are travelling in constant velocity and no forces are acting on you, back to the pendulum experiment), so you would be thinking you were just hovering in mid air and the whole world is moving the other way. However, we process what actually moves and what doesn't move and conclude that we are moving and not the world. This is my interpretation.

If anyone else has contradictory answers, i'll be glad to hear it. I may possible be wrong

EDIT: CHanged Number 2. We do not work with non-inertial frames of reference so my example was wrong.

 

[siraulo23]

Thanks for the responses

Going back to question 3. I understand that using the pendulum, we could tell that the rocket ship was accelerating but how could I tell the difference whether or not the rocket ship is stationary or moving at constant velocity?

 

[siraulo23]

Also for question 2:

I wrote down:
- a frame of reference that is at rest
- a frame of reference that is moving at constant velocity
- a frame of reference falling freely under the influence of gravitational force

Im not sure if they're right or if they actually answer the question (do i need to be specific? - "identify situations")

 

[Slowness]

Don't know about the specifics. Also, i don't think there will be any way to tell the difference between constant speed and stationary as they are both inertial frames of reference.

 

[siraulo23]

Ok, thanks