- #1
rocketboy
- 243
- 1
Hello everyone.
I've just received my gr 12 physics textbook today and began reading the chapter on Special Relativity, because I find it fascinating. So I'm new to the topic, please bear with me.
The first postulate states that "the laws of physics have the same form in all inertial reference frames".
The second states that "light propagates through empty space with a definite speed c independent of the speed of the source or observer".
I'm having difficulty connecting the two, and grasping the concept of light having the same definite speed c no matter the reference frame. Don't the laws of physics discussed in the first postulate include those in mechanics about frames of reference?
Say you are moving at 100km/hr down the road and you see a car out your window, and measure that he is doing 20km/hr (from your frame of reference) that you have to add that to your speed, to find out that his speed is actually 120km/hr to the frame of reference of somebody on the side of the road? This means that from the two different reference frames the car is doing two different speeds (relative to each frame of reference).
However, postulate 2 doesn't seem to follow this, because it says that the speed of light is definite, no matter what frame of reference the observer is in. Which in the case of my car example, isn't true.
Could somebody please explain this to me, or show me where I went wrong? I'd like to fully understand this because it's making the section on Simultaneity difficult to understand, and I'm not even going to go onto the Twin Paradox until I have this down.
Thanks.
-Jon
I've just received my gr 12 physics textbook today and began reading the chapter on Special Relativity, because I find it fascinating. So I'm new to the topic, please bear with me.
The first postulate states that "the laws of physics have the same form in all inertial reference frames".
The second states that "light propagates through empty space with a definite speed c independent of the speed of the source or observer".
I'm having difficulty connecting the two, and grasping the concept of light having the same definite speed c no matter the reference frame. Don't the laws of physics discussed in the first postulate include those in mechanics about frames of reference?
Say you are moving at 100km/hr down the road and you see a car out your window, and measure that he is doing 20km/hr (from your frame of reference) that you have to add that to your speed, to find out that his speed is actually 120km/hr to the frame of reference of somebody on the side of the road? This means that from the two different reference frames the car is doing two different speeds (relative to each frame of reference).
However, postulate 2 doesn't seem to follow this, because it says that the speed of light is definite, no matter what frame of reference the observer is in. Which in the case of my car example, isn't true.
Could somebody please explain this to me, or show me where I went wrong? I'd like to fully understand this because it's making the section on Simultaneity difficult to understand, and I'm not even going to go onto the Twin Paradox until I have this down.
Thanks.
-Jon