SPH4U 3.1 Inertial and non-inertial frames of reference
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- Опубликовано: 30 сен 2024
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@6:06 you say you're on the ground and in a "non-inertial" frame of reference. But above your definition of a non-inertial frame of reference is a frame that IS accelerating. So, I'm not sure what to think now.
I just noticed the little comment at the top of the video, never mind.
@@peterlee5726 Yes, that was a mistake in the video. Sorry!
I am struggling to calculate the fictitious force
An inertial frame is not accelerating with respect to what? Another inertial frame?
But that means to define inertial frame you are considering another inertial frame. This is circular fallacy.
Hah, good question! I see you've made a video about that very topic. For our purposes it's enough to use a stationary observer on Earth as a reference frame, but you're right that it's absolutely more complicated than that! (The Earth is not inertial, neither is the Sun, as your video points out it would be necessary to compare to an "isolated body").
Good question - in special relativity you have the nonsense: an observer A is stationary to A (A is in relative rest to A).
In a book I read this nonsense: rest is equal to motion.
@ 17:28 question b cant I just set fnet to 0 and so it would become Fn=mg would that be correct?
Hey Christian, sorry for the delay! Yeah that's right, Fnet is 0, so Fn=mg. I just used the same process as a) and c), but you'll see that a=0 in the last step.
In c, if we're accelerating downward why does the force still acts upward?
great vid! quick queation how are we supposed to know which frame of reference we should be using in the bus question?
Good question Dima - and it probably doesn't help that I used the wrong words in the video!
Basically, the laws of physics as we learn them in this course assume that we're in an *inertial* frame of reference (particularly Newton's First Law). So to solve a problem, try to use an inertial frame. The trick is to recognize when a frame isn't inertial (i.e. the bus), and try to find an inertial frame you can use instead (i.e. the ground outside the bus).
If you absolutely have to solve a problem in a non-inertial frame, then you'll need to add in fictitious forces to make everything work. You'll see more of that in 3.4 with centrifugal forces!
OnPhysics thank u so much!
You're very welcome!
for the the first question. how did you use the netfore of the horozontal component and use it in the vertical component?
Hi Muhammad! Let me know if this makes sense.
The goal is to find acceleration. At 7:28, we have an equation for Ft that came from the *vertical (y)* forces on our FBD. At 7:57, we have ma=Ft sin10, from the *horizontal (x)* forces on our FBD. We still want to find a, so we need to do something about that m and Ft.
So at 8:12, we take our horizontal equation ma=Ft sin10, and substitute in the value of Ft from earlier (vertical). That removes Ft from the equation, and also lets us cancel out m, because it's the same on both sides of the equation. Then we're left with an equation for acceleration!
Oh ok thanks!