Motion of Objects: Physics Exercise Explanation

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Homework Help Overview

The discussion revolves around the motion of cyclists and the trajectories associated with their movement as observed from a fixed reference point. The original poster presents a scenario involving two cyclists moving at constant speed and questions the nature of the trajectory of a reflector on one cyclist's wheel.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to describe the trajectories of the cyclists and the reflector, initially suggesting they are rectilinear. Participants question the accuracy of this description and explore the nature of the reflector's path, leading to the identification of a cycloid.

Discussion Status

Participants have engaged in clarifying the nature of the trajectories involved, with some suggesting that the reflector's path is a cycloid rather than a simple rectilinear motion. There is acknowledgment of corrections made regarding the shape of the trajectory, indicating a productive exploration of the topic.

Contextual Notes

There is a mention of the reflector's position on the wheel and how it affects the trajectory, with references to specific types of cycloids, such as curtate cycloids, suggesting that the original poster may have constraints in their understanding of the geometry involved.

chemistry1
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Hi, I have begun physics and we are seeing systems of reference as an introduction.Now I have a small exercise which I'm not sure of, I would need you to check if it's correct or not.

There are two cyclists A and B. Suppose that you take place on a sidewalk and look at them pass. They move to the right and to a constant speed.

What trajectory do you associate to the cyclists ? Rectilinear (so, one "x" axis.)

What answer would the cyclist A give if we asked her to determine the trajectory of cyclist B ? Rectilinear also.

Represent the trajectory of the reflector placed in the front wheel of cyclist B, such that you would see her from the sidewalk.
bicyc.jpg


The curves are halfs of a circle and I considered that the reflector began at half the height of the wheel.( so there's the highest point, middle point and the case where the reflector "touches" the ground.)

THank you !
 
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The basic idea is right, but the curves are not half-circles. Think of the moment where the reflector touches the ground. What is its speed forwards at that point? Compare this to the speed the reflector has at the top, and at the front and back of the wheel.
 
I've been suggested that it's a cycloid. Btw are the other two correct ? thank you
 
The linear things? Yes.

It is a cycloid, right.
 
mfb said:
The linear things? Yes.

It is a cycloid, right.
To be frank, I did not expect it at all... it makes me quite ashamed ^^
 
chemistry1 said:
I've been suggested that it's a cycloid. Btw are the other two correct ? thank you
The in-wheel reflectors I've seen are not that close to the periphery of the wheel. The curve would be a curtate cycloid. http://en.wikipedia.org/wiki/Cycloid#Related_curves
 
Yeah, it makes more sense. Thanks for the correction!
 

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