Sticking Of Person With The Wall Of Rotor

Edited By Vishal kumar | Updated on Jul 02, 2025 06:52 PM IST

Have you ever seen an object fly off a spinning merry-go-round or tried to hold a book fixed on a rotating table? These everyday occurrences manifest rather interesting dynamics of objects on a rotating platform. Skidding-unfastening of objects- forwards and sideways- is both amusing and hazardous, depending on the situation. In this paper, we will be engaged in understanding the physics of objects skidding on moving platforms in the line of duty which involves friction, centripetal force, and inertia, among others. In furtherance to this, we will discuss some related practical implications such as how objects can be secured on a moving surface and what principle keeps rotating machines and amusement rides securely in place. In this article, we will cover the concept of Skidding of Object on a Rotating Platform. This concept falls under the broader category of laws of motion.

Sticking Of Person With The Wall Of Rotor

Skidding of Object on a Rotating Platform

Centrifugal force ≤ Force of friction mω2r≤μmg∴ωmax=μgr= It is the maximum angular velocity of rotation of the platform so that the object will not skid on it. ω= Angular velocity r= radius μ= coefficient of friction

Solved Examples Based on Sticking of Person With the Wall of Rotor

Example 1: As shown in the figure, a person of mass 'm' remains stuck to the wall of the rotating rotor. What should be the minimum value of angular velocity ω [coefficient of friction between wall and man is μ]

1) μgR
2) gR
3) gμR
4) μgR

Solution:

Sticking of Person with the wall of Rotor(Death well)

F= weight of person (mg)μR=mgμFc=mgμmωmin2r=mg∴ωmin=gμr Where F= friction force Fc= centrifugal force ωmin= minimum angular velocity μ= coefficient of friction r= radius of Rotor

From the figure

fr=mgμN=mg[fr=μN]μFc=mg[AsN=Fc]μmωmin2R=mg⇒ωmin=gμR

Hence, the answer is the option (3).

Example 2: A man is resting against the inner wall of a rotor which is moving with angular velocity ω. If the radius of the rotor is 2m and the coefficient of static friction between the wall and the person is 0.2. Find the minimum angular velocity (in rad/sec) for man to be at rest. (g= 10m/s²)

1) 5

2) 8

3) 10

4) 15

Solution

Sticking of Person with the wall of Rotor(Death well)

F = weight of person (mg)

μR=mgμFc=mgμmωmin2r=mg∴ωmin=gμr

wherein

F = friction force

F_c = centrifugal force

W_min = minimum angular velocity

μ=coefficient of friction

r = radius of Rotor

N=mw2Rfs=μN=μmw2R
For the Resting position of the person

:fs=mg⇒μm2R=mgμω2R=gω2=gμR⇒100.2×2=25ω=5rad/sec

Hence, the answer is the option (1).

Example 3: A person stands in contact against the inner wall of a rotor of radius r. The coefficient of friction between the wall and the clothing is μ and the rotor is rotating about a vertical axis. What is the minimum angular speed of the rotor so that the person does not slip downward?

1) gμr
2) gμ
3) 2gμr
4) 1μr

Solution:

For the circular motion of the person
N=mrω2
Now for the vertical motion of the person

f=fmax=μNf=μmrω2

We also know f=mg

μmrω2=mgω=gμr

Hence, the answer is the option (1).

Example 4: A man of 50 pounds was made to stand against the inner wall of a hollow cylinder and the rotor of radius 5m is rotating at its vertical axis, and the coefficient of friction between the wall and his clothing is 0.35. What is the minimum angular speed of the rotor so that the person does not slip downward?

1) 2rads−1
2) 6rads−1
3) 5rads−1
4) 0.3rads−1

Solution:

The cylinder is in a vertical position. The normal reaction of the wall on man acts horizontally and it is equal to the centripetal force acting on it.

R=mrω2

Then the frictional force acts upward

F=mg

The man will still remain stuck to the wall after the floor is removed he will continue to rotate with the cylinder
μ≥FRF≤μRmg≤μmrω2ω2≤gμRω≤gμR
The minimum angular speed of rotation

ω=gμRμ=0.35,r=5 m,g=9.8 m/s2ω=9.80.35×5ω=2.31rads−1=2rads−1

Hence, the answer is the option (1).
Summary
Skidding on a rotating platform might happen since the frictional force between that object and the platform may not be sufficient to produce the needed centripetal force to keep it in its curved path. Because the platform rotates, the centripetal force pulls the object toward the centre. However, should the friction become too low because of a very smooth surface, large speed, or a heavy mass of the object, then the inertia of the object will just slide it outward. This very effect is what makes things slide off a lazy Susan and what keeps people safe on amusement park rides where they would skid if not for the safety features built into their ride. Something must be done in order to ensure adequate friction to keep things from skidding. Non-slip surfaces or proper tethering of objects will do the trick. Knowing these concepts a rotating platform or ride can be designed and run much safer from accident.

Frequently Asked Questions (FAQs)

1. What would happen if the rotor's surface was frictionless?

If the rotor's surface was frictionless, the person would not be able to stick to the wall when it's vertical, regardless of speed. They would slide down due to gravity. In a horizontal position, they could still be held in place by the normal force.

2. Can the principle of the rotor be observed in everyday life?

Yes, this principle can be observed in many everyday situations, such as water staying in a bucket when swung in a vertical circle, clothes sticking to the sides of a washing machine during the spin cycle, or riders being pressed against the sides of a rotating carnival ride.

3. How does the person's mass affect the required rotation speed?

The person's mass doesn't directly affect the required speed. The centripetal force increases proportionally with mass, but so does the person's weight. However, a heavier person might experience more friction, potentially allowing them to stick at slightly lower speeds.

4. What's the difference between centripetal and centrifugal force in this context?

Centripetal force is the real force acting towards the center that keeps the person moving in a circular path. Centrifugal force is the apparent outward force felt by the person, which is actually the inertia resisting the centripetal force. In the rotor's reference frame, it appears as if an outward force is pushing the person against the wall.

5. How does the coefficient of friction between the person and the wall affect the experiment?

The coefficient of friction is crucial. A higher coefficient allows the person to stick to the wall at lower speeds or steeper angles. With a very low coefficient, much higher speeds would be required to keep the person in place, especially when the rotor is vertical.

6. Is there a minimum speed required for the person to stick to the wall?

Yes, there is a minimum speed. The rotor must spin fast enough so that the centripetal force, combined with friction, exceeds the person's weight. Below this speed, the person would slide down or fall.

7. What is the principle behind a person sticking to the wall of a rotor?

The principle is centripetal force. As the rotor spins, it creates an outward force that pushes the person against the wall. This force, combined with friction between the person and the wall, keeps them in place even when the rotor is vertical.

8. Why doesn't the person fall when the rotor is vertical?

The person doesn't fall because the centripetal force pushing them against the wall is greater than the force of gravity pulling them down. The friction between the person and the wall provides the necessary force to counteract gravity.

9. What role does friction play in this phenomenon?

Friction between the person and the wall is crucial. It provides the force that prevents the person from sliding down when the rotor is vertical. Without sufficient friction, the person would fall regardless of the rotation speed.

10. How does the speed of rotation affect the force on the person?

The faster the rotor spins, the greater the centripetal force on the person. This force increases with the square of the angular velocity, so doubling the speed quadruples the force.

11. Could this principle be used in space to create artificial gravity?

Yes, this principle could be used to create artificial gravity in space. By rotating a large cylindrical structure, the centripetal force could simulate gravity for inhabitants inside, pushing them towards the outer wall.

12. Can a person move within the rotor while it's spinning?

Yes, a person can move within the rotor while it's spinning, but it requires effort. They would need to overcome the apparent centrifugal force pushing them against the wall. Moving "up" or "down" relative to the rotor's orientation would feel like climbing a steep hill.

13. What would happen if the rotor's rotation axis was not perfectly vertical?

If the rotor's axis was tilted, the person would experience a varying force as they rotated. The force would be greatest when they're at the lowest point of the rotation and least at the highest point, potentially causing a feeling of "rising and falling" with each rotation.

14. How does the rotor experiment relate to planetary motion?

The rotor experiment is analogous to planetary motion in that both involve centripetal force. In the case of planets, gravity provides the centripetal force that keeps them in orbit around the sun, just as the wall provides the force that keeps the person moving in a circle.

15. How does blood circulation in the human body relate to the rotor experiment?

Blood circulation involves similar principles to the rotor experiment. When a person is subjected to high g-forces, like in a fast-spinning rotor or a fighter jet making a tight turn, blood can be forced away from the brain towards the lower body, potentially causing loss of consciousness.

16. What safety precautions are necessary when operating a human-scale rotor?

Safety precautions include ensuring the rotor is structurally sound, gradually increasing and decreasing speed, limiting maximum speed, providing proper restraints or handholds, ensuring participants are in good health, and having emergency stop mechanisms.

17. How does the rotor experiment demonstrate the concept of apparent weight?

The rotor demonstrates apparent weight by showing how rotational motion can create a force that adds to or subtracts from the normal force experienced due to gravity. When spinning, a person feels "heavier" due to the additional centripetal force.

18. What would happen if the rotor was filled with water instead of air?

If the rotor was filled with water, the person would experience additional resistance due to the water's viscosity. The water itself would also be subject to the rotational forces, creating a pressure gradient from the center to the edge of the rotor.

19. How does the rotor experiment relate to the concept of gravitational slingshot in space missions?

While not directly related, both involve manipulating an object's path using existing forces. In a gravitational slingshot, a spacecraft uses a planet's gravity and motion to gain speed, similar to how the rotor uses its wall to change the person's direction continuously.

20. Can the rotor principle be used to generate energy?

While the rotor itself doesn't generate energy, similar principles are used in some energy storage systems. Flywheels, for instance, store energy as rotational kinetic energy and can be used to smooth out fluctuations in power grids.

21. How does the rotor experiment demonstrate the difference between inertial and non-inertial reference frames?

The rotor demonstrates the difference between inertial and non-inertial frames clearly. From an outside (inertial) perspective, the centripetal force from the wall causes the person's circular motion. From inside the rotor (non-inertial frame), it appears as if an outward "centrifugal force" is pushing the person against the wall.

22. Can the rotor principle be used to create variable gravity environments for research?

Yes, rotating structures can create variable gravity environments. By adjusting the rotation speed and radius, different levels of artificial gravity can be produced. This could be useful for space research or for creating reduced gravity environments on Earth.

23. How does the thickness of the rotor wall affect the experiment?

The thickness of the rotor wall doesn't directly affect the physics of the experiment. However, a thicker wall would make the rotor more rigid and stable, potentially allowing for higher safe operating speeds and reducing vibrations.

24. Can the principles of the rotor be applied to understand weather patterns?

Yes, the principles demonstrated by the rotor are relevant to understanding weather patterns, particularly cyclones and anticyclones. The balance between pressure gradient forces and the Coriolis effect in these weather systems is analogous to the balance of forces in the rotor.

25. How would the experience in the rotor differ on other planets with different gravities?

On planets with lower gravity, like Mars, a lower rotational speed would be required for the person to stick to the wall when vertical. On planets with higher gravity, like Jupiter, a higher speed would be needed. The basic principle would remain the same, but the required forces would differ.

26. How does the rotor experiment relate to the concept of angular momentum conservation?

While the rotor itself doesn't demonstrate angular momentum conservation, the principle is related. If a person in the rotor were to move closer to the center while it's spinning, they would spin faster to conserve angular momentum, similar to an ice skater pulling in their arms.

27. Can the rotor principle be used to simulate different gravity environments for plant growth experiments?

Yes, rotational systems can be used to create artificial gravity environments for plant growth experiments. By adjusting the rotation speed and radius, different gravity levels can be simulated, allowing researchers to study how plants grow under various gravitational conditions.

28. How does the flexibility of the human body affect the experience in the rotor?

The flexibility of the human body can affect the rotor experience. A more flexible person might be able to distribute the forces more evenly across their body, potentially feeling more comfortable. However, excessive flexibility could also lead to more movement and potential instability.

29. What would happen if multiple people were in the rotor simultaneously?

With multiple people in the rotor, each person would experience the same centripetal force based on their position. However, they might affect each other through physical contact or by changing the rotor's mass distribution, potentially influencing its rotation or stability.

30. Can the principles of the rotor be applied to understand the formation of galaxies?

While greatly simplified, the rotor does demonstrate some principles relevant to galaxy formation. The balance between centripetal force and gravity that keeps the person on the rotor wall is analogous to the balance that keeps stars in their galactic orbits. However, galaxy formation involves many more complex factors.

31. How does the rotor experiment relate to the principle of equivalence in general relativity?

The rotor experiment relates to the principle of equivalence in that the "artificial gravity" created by the rotation is locally indistinguishable from real gravitational force. This is similar to how the principle of equivalence states that the effects of gravity are indistinguishable from the effects of acceleration in a small enough region of spacetime.

32. What happens if the rotor suddenly stops?

If the rotor suddenly stops, the person would fall. The centripetal force would disappear instantly, leaving only friction to counteract gravity, which wouldn't be enough to keep the person in place.

33. Can a person stick to the wall if the rotor is spinning too fast?

Yes, but it can be dangerous. Extremely high speeds can cause discomfort, disorientation, or even injury due to the intense forces on the body. There's typically an optimal range of speeds for safety and comfort.

34. How does the radius of the rotor affect the force on the person?

The centripetal force increases with the radius of the rotor. For the same angular velocity, a larger radius results in a greater linear velocity and thus a larger centripetal force.

35. How does the angle of the rotor affect the required speed?

As the rotor tilts from horizontal to vertical, a higher speed is required to keep the person in place. When vertical, the speed must be high enough for the centripetal force and friction to overcome gravity completely.

36. Why do people feel "heavier" in a spinning rotor?

The feeling of being "heavier" is due to the additional force from the rotation. The centripetal force adds to the normal force between the person and the wall, creating a sensation similar to increased weight or gravity.

37. How does air resistance affect the person in the rotor?

Air resistance has a minimal effect on the person sticking to the wall. The main forces at play are centripetal force, friction, and gravity. Air resistance might slightly increase the perceived force at very high speeds but is generally negligible.

38. How does the person's orientation affect their experience in the rotor?

The person's orientation can significantly affect their experience. Lying parallel to the axis of rotation typically feels more comfortable than standing perpendicular to it, as it distributes the force more evenly across the body.

39. How does the concept of inertia relate to the rotor experiment?

Inertia plays a crucial role in the rotor experiment. It's the tendency of the person to continue moving in a straight line that creates the need for the centripetal force. The wall of the rotor provides this force, constantly changing the person's direction to keep them in circular motion.

40. What would happen if the rotor changed its rotation speed suddenly?

If the rotor suddenly increased speed, the person would feel a stronger force pushing them against the wall. If it suddenly decreased speed, they might feel like they're "falling" towards the bottom of the rotor as the centripetal force decreases.

41. How does the rotor experiment demonstrate Newton's First Law of Motion?

The rotor experiment demonstrates Newton's First Law by showing that an object (the person) tends to continue in a straight-line motion unless acted upon by an external force. The wall of the rotor provides this force, constantly changing the person's direction to keep them in circular motion.

42. Can the principles of the rotor be applied to design safer vehicles?

Yes, understanding centripetal force is crucial in vehicle design, especially for cornering. Car suspensions and tire designs are optimized to provide the necessary centripetal force for turning without skidding, similar to how the rotor's wall provides force to keep the person in place.

43. How does the concept of centripetal acceleration apply to the rotor?

Centripetal acceleration is the change in velocity needed to keep an object moving in a circular path. In the rotor, this acceleration is constantly directed towards the center of rotation. Its magnitude is proportional to the square of the angular velocity and the radius of the rotor.

44. Can the principles of the rotor be used to separate mixtures?

Yes, this principle is used in centrifuges to separate mixtures. By rotating at high speeds, denser components experience a stronger centrifugal effect and move farther from the axis of rotation, while less dense components stay closer to the center.

45. What would happen if the person in the rotor tried to throw an object?

If a person in the spinning rotor threw an object, its path would appear curved from their perspective due to the Coriolis effect. From an outside view, the object would move in a straight line tangent to the circle at the point it was released, demonstrating inertia.

46. How does the rotor experiment relate to the formation of accretion disks in space?

The rotor experiment demonstrates principles similar to those in accretion disk formation. In both cases, material is held in a circular path by a central force (the rotor wall or gravity), and friction plays a role in the system's behavior.

47. What would happen if the rotor was spinning in a vacuum?

If the rotor was spinning in a vacuum, the basic principles would remain the same. The main difference would be the absence of air resistance, which could allow for higher rotational speeds. The person inside would still stick to the wall due to centripetal force.

48. How does the rotor experiment relate to the concept of escape velocity?

While not directly related, both involve overcoming a central force. In the rotor, the rotational speed must be high enough for the centripetal force to overcome gravity. Similarly, escape velocity is the speed needed for an object to overcome a planet's gravitational pull.

49. What would happen if the rotor's radius changed while spinning?

If the rotor's radius increased while spinning at a constant angular velocity, the centripetal force on the person would increase, making them feel more pressed against the wall. If the radius decreased, they would feel less force. This demonstrates the relationship between radius and centripetal force.

50. How does the rotor experiment demonstrate the concept of mechanical equilibrium?

The rotor demonstrates mechanical equilibrium when the person remains stationary relative to the rotating wall. At this point, the centripetal force provided by the wall, friction, and the person's weight are in balance, resulting in no net force in the rotating frame of reference.