Normal force physics question (1 Viewer)

[StudyOnly]

Hello this is just a question that's been annoying me.

You will need to video:

So my question is why he keeps the normal force positive in the video (i.e. why does he get 530N, not -530N if outwards in negative and inwards is positive). Also if Fc keeps increasing as you go faster there comes a point where Fc will become larger than mg and cause a negative N which will mean it acts downwards (according to the logic of the video) with mg, this means the car will stay down (then why is it if you go over a hill fast you get airborne).
Fc = mg - N
N = mg - mv^2/r
if v is large the N becomes negative hence acts downwards

Thanks!

 

[Drdusk]

The reason is because he has made a small technical error. Now this doesn't really mean much because usually in Physics problems you just get the magnitude first and then you figure out the direction yourself manually.

His technically error is in his 4th line. He stated that


Now in sigma notation as he stated it is.



The sigma as you know just means Sum, so your actually technically adding mg with the Normal force.
So translating it word for word from sigma notation would give you:



In his working he has already accounted for the fact that the Normal force will be negative which gives you -Fn instead of +Fn. As a consequence of this you get a positive answer for the normal force, but if you did it like how I've detailed above, it will be negative, as I have not manually accounted for the fact that it will be negative in the equation.

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Now the last bit is just a small bit of misunderstanding. The centripetal force physically isn't actually a force, rather it is a direct result of other forces.
The equation does NOT hold true for every single value of v.

for all . The normal force must always be greater than zero so we can actually find out the maximum speed for which this equation holds true.



Solving for v gives us..



This is the MAX speed for which the sum provides the centripetal force.

After this limit has been reached is NOT true, i.e. after this speed , as the bicycle/car will be airborne. Which makes sense as there's no centripetal force keeping its circular motion

This is a great question, it shows you are actually thinking about the concepts rather than just accepting them. Keep it up

 

[StudyOnly]

The reason is because he has made a small technical error. Now this doesn't really mean much because usually in Physics problems you just get the magnitude first and then you figure out the direction yourself manually.

His technically error is in his 4th line. He stated that


Now in sigma notation as he stated it is.



The sigma as you know just means Sum, so your actually technically adding mg with the Normal force.
So translating it word for word from sigma notation would give you:



In his working he has already accounted for the fact that the Normal force will be negative which gives you -Fn instead of +Fn. As a consequence of this you get a positive answer for the normal force, but if you did it like how I've detailed above, it will be negative, as I have not manually accounted for the fact that it will be negative in the equation.

------------------------------------------

Now the last bit is just a small bit of misunderstanding. The centripetal force physically isn't actually a force, rather it is a direct result of other forces.
The equation does NOT hold true for every single value of v.

for all . The normal force must always be greater than zero so we can actually find out the maximum speed for which this equation holds true.



Solving for v gives us..



This is the MAX speed for which the sum provides the centripetal force.

After this limit has been reached is NOT true, i.e. after this speed

This is a great question, it shows you are actually thinking about the concepts rather than just accepting them. Keep it up

Thanks for the great answer!