
#1
Feb2112, 05:36 PM

P: 16

In the figure, at the point where the orange car is at, what is preventing the car from falling down to the earth? Where does the force [tex]\vec{F}_u[/tex] comes from? From the car's velocity? If so, how could it? Isn't the velocity at the point completely in the x direction? Thus, there is no y direction to counteract the pull of gravity and centripetal force. In this case, is the centripetal force created by the car's weight and the "normal force"? By normal force, i mean that the car drives into the loopdloop and that creates the normal force. Also, is there even a normal force when the car is at the point where the orange car is? sorry :( i find this really confusing. I want to say the centrifugal "force" is creating upward force necessary to keep car from falling, but where does it come from? The force of the weight is provided by the earth, the centripetal force is provided by...??? Thanks in advance. 



#2
Feb2112, 06:11 PM

P: 861

The car is falling. Just as a stone is falling when you throw it horizontally. It's moving so fast horizontally at the same time that you might not notice it falling. (In fact the flattish top of the parabola is, to second order, a circle, and if you pursue this argument, the familiar g =v^2/r formula emerges.)
(In the case of the car, if moving very fast, the drum is probably forcing it fall (as it follows the curve) faster than it would fall if there were no drum.) 



#3
Feb2112, 06:29 PM

Mentor
P: 40,875





#4
Feb2112, 11:15 PM

HW Helper
P: 6,925

Centrifugal/Centripetal force
It may be easier to understand this by looking at the acceleration involved. At the top of the loop, assuming the car is moving fast enough and the radius of the path is small enough (v^{2} / r >= 1 g), then the moving point of contact between car and looped track is accelerating downwards at or greater than 1 g, so the car remains in contact with the track because the point of contact is accelerating downwards faster than gravity is accelerating the car away from the point of contact.




#5
Feb2212, 01:26 PM

P: 1,506

I would reinforce Doc Al's statement . There is no Fu. There are only 2 forces acting on the car
1)gravity 2)the (normal) reaction of the track The resultant force has a value of mv^2/r or mω^2r 


Register to reply 
Related Discussions  
Centripetal and centrifugal force  Classical Physics  24  
Centrifugal and centripetal force question: racecar and banked curve question  Introductory Physics Homework  12  
centripetal and centrifugal force  General Physics  58  
Centripetal/centrifugal force  General Physics  6  
Centripetal/Centrifugal Force and Moment of Inertia  Classical Physics  6 