Minimum Velocity Required for Loop-The-Loop Problem

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In summary, the minimum velocity required for a particle to safely complete a loop is just a little more than 2√gr.
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JackFyre
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A question regarding the minimum velocity required by a particle to 'do a loop' without falling-

Assuming the particle has a velocity v before reaching the loop. Then-
KE = mv²/2, at the bottom of the loop.

potential energy at the top-most point of the loop= 2mgr (2r = h)
then, by the law of conservation of energy, mv²/2 = 2mgr, and we get v = 2√gr
in this case, the particle will have zero kinetic energy at the the top of the loop, an will fall, as it has 0 velocity. However, if the initial velocity were slightly higher, say v+Δv, then the particle will have some velocity a the top of the loop.

By this logic, should not the minimum velocity for a particle to safely complete a loop be just a little more than 2√gr ?
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In order for the particle to complete the loop, the normal force from the track onto the particle must be nonzero.

Do you see what that implies for the minimum velocity ( and hence kinetic energy ) the particle must have at the top of the loop?
 
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JackFyre said:
. . . by the law of conservation of energy, mv²/2 = 2mgr, and we get v = 2√gr
in this case, the particle will have zero kinetic energy at the the top of the loop, an will fall, as it has 0 velocity.
The particle will lose contact with the track before it reaches the top. When that happens, it will describe a parabolic trajectory inside the loop and land on the opposite side of the track. The kinetic energy will never go to zero. Reaching zero KE could be the case if one had a bead on a ring that is constrained to stay on the circle and the normal force is allowed to change direction from radially in to radially out.
 
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kuruman said:
The particle will lose contact with the track before it reaches the top. When that happens, it will describe a parabolic trajectory inside the loop and land on the opposite side of the track. The kinetic energy will never go to zero. Reaching zero KE could be the case if one had a bead on a ring that is constrained to stay on the circle and the normal force is allowed to change direction from radially in to radially out.
Thanks, that clears it up!
 
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FAQ: Minimum Velocity Required for Loop-The-Loop Problem

What is the minimum velocity required for a loop-the-loop?

The minimum velocity required at the top of the loop can be found using the equation \( v = \sqrt{g \cdot r} \), where \( g \) is the acceleration due to gravity (9.8 m/s²) and \( r \) is the radius of the loop. This ensures that the centripetal force is sufficient to keep the object in circular motion.

How do you derive the minimum velocity for a loop-the-loop?

To derive the minimum velocity, consider the forces acting on the object at the top of the loop. The gravitational force must be equal to the centripetal force required to keep the object in circular motion. Setting \( mg = \frac{mv^2}{r} \) and solving for \( v \) gives \( v = \sqrt{g \cdot r} \).

What happens if the velocity is less than the minimum required for a loop-the-loop?

If the velocity is less than the minimum required, the object will not have enough centripetal force to stay on the circular path and will fall off the track, failing to complete the loop.

Does the mass of the object affect the minimum velocity required for a loop-the-loop?

No, the mass of the object does not affect the minimum velocity required. The minimum velocity depends only on the radius of the loop and the acceleration due to gravity, as mass cancels out in the derivation of the equation.

How does the radius of the loop affect the minimum velocity required for a loop-the-loop?

The radius of the loop directly affects the minimum velocity required. A larger radius requires a higher minimum velocity, as given by the equation \( v = \sqrt{g \cdot r} \). Conversely, a smaller radius requires a lower minimum velocity.

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