How is the Centripetal Force Created in a Loop-de-Loop?

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In summary, at the top of the loop, the centripetal force that keeps the car from falling is provided by the combination of gravity and the normal force from the track. The car's velocity and angular velocity also play a role in maintaining this circular motion.
  • #1
rainstom07
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RNXOr.gif


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 loop-d-loop 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.
 
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  • #2
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.)
 
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  • #3
rainstom07 said:
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?
There's no such force. All forces acting on the car at that point act downward.

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.
What matters is the direction of the car's acceleration, which is downward. To maintain the circular motion, the car requires a net downward 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 loop-d-loop 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?
Sure, as long as the car is moving fast enough.

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...?
Forget about centrifugal force (that's only useful when describing things from a rotating frame). Gravity and the normal force provide the centripetal force.
 
  • #4
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 (v2 / 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
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
 

1. What is the difference between centrifugal and centripetal force?

Centrifugal force is a fictitious force that appears to act outward on a rotating object, while centripetal force is the actual force that pulls an object towards the center of the rotation.

2. How are centrifugal and centripetal forces related?

Centrifugal and centripetal forces are directly related, as the centripetal force is necessary to counteract the centrifugal force and keep an object moving in a circular path.

3. How do centrifugal and centripetal forces affect the motion of objects?

Centrifugal and centripetal forces play a crucial role in circular motion, as they are responsible for keeping objects in orbit, maintaining balance in rotating systems, and causing objects to move in curved paths.

4. What factors affect the strength of centrifugal and centripetal forces?

The strength of centrifugal and centripetal forces depends on the mass of the object, the speed of the rotation, and the distance from the center of rotation.

5. How do centrifugal and centripetal forces impact everyday life?

Centrifugal and centripetal forces have a significant impact on everyday life, from the motion of objects in amusement park rides to the functioning of washing machines and the Earth's rotation around the sun.

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