- #1
mancity
- 26
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- Homework Statement
- why is the normal force at the top of a rollercoaster loop the same direction as the force of gravity?
- Relevant Equations
- f_n+f_g=f_c
Is the normal force at the top of a rollercoaster loop always directed upwards?
- Thread starter mancity
- Start date
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- Tags
- Circular motion
In summary, the normal force at the top of a rollercoaster loop is not always directed upwards. At the top of the loop, the normal force can act downward or upward depending on the speed of the rollercoaster. If the coaster is moving fast enough, the normal force will still act upwards, contributing to the centripetal force needed to keep the coaster on the track. However, if the speed decreases significantly, the normal force may not be sufficient to overcome gravitational force, potentially resulting in a downward direction of the normal force or even losing contact with the track.
- #2
Halc
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Coincidence that they are depicted nearly equal, but the gravity vector is a function only of mass (and distance from Earth if it's a really tall loop), whereas the normal force is a function of mass, loop radius, and the speed at which the loop is taken.mancity said:
That the normal vector at top and bottom appear similar implies implausibly that the speed is the same at top and bottom.
That the sum of the two component vectors in opposite direction add up to a larger magnitude vector is just wrong.
I also have issues with afelt since one does not 'feel' gravitational acceleration. The guys in the ISS feel weightless despite having a coordinate acceleration in the frame of Earth.
- #3
jbriggs444
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The left hand side of that drawing seems misleading. The sum of two oppositely directed vectors should not have a larger magnitude than either.mancity said:
- #4
Lnewqban
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Welcome, @mancity !mancity said:
The direction of any normal force is always perpendicular to the surface of contact between two bodies.
Therefore, in the case of the shown circle, the direction of the normal force at any point should be pointing towards or away the center of the geometrical circle.
The diagram represents the external forces acting on the car; hence, the normal shows the force with which the track is pushing against the wheels of the car: pointing always to the center of the loop.
Please, see:
https://www.physicsclassroom.com/class/circles/Lesson-2/Amusement-Park-Physics
- #5
Cutter Ketch
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I believe the idea they are trying to convey is that the coaster is moving so fast and the curvature of the top of the hill is so tight that it takes more than just the force of gravity to keep the train on the tracks. The required v^2/r is greater than g, so there must be another downward force.
In those cases the rider feels negative g’s. (This is one of the things love about modern rollercoasters, so it’s very common). You float up in your seat and the only thing that keeps you from flying out of the car is the shoulder harness holding you down. More properly from the point of view of physics, the force of gravity isn’t enough to keep you following the train around the tightly curved top of the hill and you need an extra force holding you down.
Well, in those moments when you need an extra downward force to stay in the car it must also be true that the car needs an extra downward force to stay on the track. How do they manage that? If you look at the wheels of a modern steel coaster, you’ll see that they don’t just have wheels on top of the track. The wheels are in a bracket that has wheels on the top, sides, and bottom of the tubular steel track. That means that the wheels can hold down as well as hold up. The riders can experience negative Gs, and in those cases the presence of the underside wheels allow the track to provide a downward normal force so the train stays on the tracks.
In those cases the rider feels negative g’s. (This is one of the things love about modern rollercoasters, so it’s very common). You float up in your seat and the only thing that keeps you from flying out of the car is the shoulder harness holding you down. More properly from the point of view of physics, the force of gravity isn’t enough to keep you following the train around the tightly curved top of the hill and you need an extra force holding you down.
Well, in those moments when you need an extra downward force to stay in the car it must also be true that the car needs an extra downward force to stay on the track. How do they manage that? If you look at the wheels of a modern steel coaster, you’ll see that they don’t just have wheels on top of the track. The wheels are in a bracket that has wheels on the top, sides, and bottom of the tubular steel track. That means that the wheels can hold down as well as hold up. The riders can experience negative Gs, and in those cases the presence of the underside wheels allow the track to provide a downward normal force so the train stays on the tracks.
- #6
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@mancity did not ask about magnitudes, only directions.Halc said:
Two bodies in contact exert equal and opposite repulsive forces on each other. The components of these two forces which are normal to the plane of contact are called the normal forces.mancity said:
At the top of the loop, the track is above the cart, so a repulsive force exerted by the track on the cart is necessarily downwards, making it the same direction as gravity.
Did you think that the normal force on a body always acts upwards? I have seen that misunderstanding before.
FAQ: Is the normal force at the top of a rollercoaster loop always directed upwards?
What is the normal force in the context of a rollercoaster loop?
The normal force is the perpendicular contact force exerted by a surface on an object in contact with it. In a rollercoaster loop, it is the force exerted by the track on the rollercoaster car.
Is the normal force at the top of a rollercoaster loop always directed upwards?
No, the normal force at the top of a rollercoaster loop is directed downwards. At the top of the loop, the track is above the car, so the normal force exerted by the track is directed towards the center of the loop, which is downwards.
How does the direction of the normal force change throughout the rollercoaster loop?
The direction of the normal force changes as the rollercoaster car moves through the loop. At the bottom of the loop, the normal force is directed upwards, while at the top of the loop, it is directed downwards. On the sides of the loop, the normal force is directed horizontally towards the center of the loop.
What role does the normal force play in the motion of the rollercoaster car through the loop?
The normal force, along with gravitational force, provides the centripetal force necessary to keep the rollercoaster car moving in a circular path through the loop. It ensures that the car stays on the track and follows the curvature of the loop.
Can the normal force be zero at the top of the rollercoaster loop?
Yes, the normal force can be zero at the top of the loop if the gravitational force alone provides the necessary centripetal force to keep the car in circular motion. This occurs when the speed of the rollercoaster car is just right so that the gravitational force equals the required centripetal force, resulting in no additional normal force from the track.