Question

A Ferris wheel rotates slowly about a horizontal axis. Passengers sit on seats that remain horizontal on the Ferris wheel as it rotates. Which type of force provides the centripetal acceleration on the passengers when they are at the top of the Ferris wheel? a) centrifugal c) gravity b) normal d) tension

Short answer

Answer: b) Normal

Step-by-step solution

A. Centrifugal#ac_tag_content# Centrifugal force is a fictitious force that acts outward in a rotating frame, away from the center of rotation. It is not a real force, and thus, it cannot provide the centripetal acceleration on the passengers when they are at the top of the Ferris wheel.

B. Normal#ac_tag_content# Normal force is a force exerted by a surface that supports the weight of an object resting on it, acting perpendicular to the surface. In the case of a Ferris wheel, the normal force acts between the passengers and the seats. At the top of the Ferris wheel, the normal force points inwards and contributes to the centripetal acceleration.

C. Gravity#ac_tag_content# Gravity is the force that attracts every object towards the center of the Earth. At the top of the Ferris wheel, the gravitational force acts vertically downward, towards the center of the Earth. As gravity is not directly towards the center of the circle at the top, gravity alone cannot provide centripetal acceleration.

D. Tension#ac_tag_content# In the context of a Ferris wheel, tension is a force exerted by the supports to keep the passengers in their seats and is not directly related to providing centripetal acceleration at the top of the Ferris wheel. Considering all the options, the correct answer is: b) Normal

Key concepts

Centrifugal Force

When learning about motion in a circular path, the term 'centrifugal force' often comes up. However, it's essential to understand that centrifugal force is not a real force, but rather a perceived force that occurs only in a rotating reference frame. Imagine you're on a merry-go-round – you might feel as though you're being pushed outward, away from the center. This sensation is due to the inertia of your body, which resists the change in motion provided by the moving merry-go-round, and not because an actual outward force is being applied.

Because it is a fictitious force, centrifugal force does not contribute to the centripetal acceleration needed to keep an object moving in a circle. Instead, this 'force' is a result of other, real forces influencing an object in a rotating system, such as the tension in a string or the friction between surfaces. To understand the true forces at play, we must look at the situations without considering the rotating frame of reference.

Normal Force

The normal force is a fundamental concept in physics, especially when discussing contact forces between objects. It acts perpendicular to the surface at the point of contact, providing support to objects. For a passenger sitting at the top of a Ferris wheel, the normal force is exerted by the seat, which pushes upward against the passenger, directly opposing gravity's pull. This force is essential for creating the centripetal acceleration that keeps the passenger moving in a circular path. Without the normal force, the passenger would not be able to remain in a stable position on the Ferris wheel.

In simple terms, when you're sitting at the top of the Ferris wheel, it is the normal force from the seat that's pushing you towards the center of the circular path, providing the necessary centripetal force to keep you in motion along the wheel's arc.

Gravitational Force

Gravitational force, one of the four fundamental forces in physics, is what keeps us anchored to the Earth. It is an attractive force that exists between all masses. On a Ferris wheel, when passengers reach the top, they are subject to this force pulling them down towards the Earth's center. However, because gravitational force acts vertically downwards, it doesn't provide the necessary horizontal component for centripetal acceleration at the top of the Ferris wheel's rotation.

It's critical to understand that while gravity contributes to the forces a rider feels, it's not responsible for keeping them moving in a circle. That role belongs to other forces that can be directional, such as the normal force from the Ferris wheel seat, which during certain points of the ride, can align with the gravitational force.

Tension Force

The concept of tension is another key player in understanding forces within certain systems, such as ropes, cables, or, as with our Ferris wheel, the supporting structures that hold the seats. Tension force is a pull exerted by a string, rope, cable, or similar object upon being stretched. While tension is critical for the structural integrity of the Ferris wheel and ensuring that the seats stay attached, it does not directly contribute to the centripetal acceleration of the passengers at the top of the Ferris wheel.

Tension forces ensure that the components of the Ferris wheel remain safely connected but do not directly cause the inwards movement required for circular motion. Instead, they work in conjunction with other forces, such as the normal force, to maintain the Ferris wheel's motion and the safety of its passengers.