How Does a Coin Roll in a Circle Without Falling?

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SUMMARY

The discussion centers on the mechanics of a coin rolling in a circular path without falling, specifically addressing the forces acting on the coin. The key takeaway is that friction plays a crucial role in providing the necessary centripetal force, allowing the coin to maintain its circular motion while tilting inward. The coin's center of mass follows a circular trajectory due to the combination of gravitational force and the normal force, with friction ensuring that the coin does not fall outward. Understanding these dynamics clarifies the conditions under which the coin can successfully roll in a circle.

PREREQUISITES
  • Basic understanding of Newton's laws of motion
  • Familiarity with the concepts of centripetal force and circular motion
  • Knowledge of friction and its role in motion
  • Concept of center of mass in rigid body dynamics
NEXT STEPS
  • Research the role of friction in circular motion
  • Study the principles of rotational dynamics
  • Explore the concept of center of mass in more detail
  • Learn about the effects of different surfaces on rolling motion
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in understanding the mechanics of motion, particularly in the context of circular dynamics and frictional forces.

Sam_Goldberg
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Hi guys, I have an extremely simple conceptual question. According to my textbook (in a problem), "if you start a coin rolling on a table with care, you can make it roll in a circle... the coin leans inward, with its axis tilted." I ask: how is this possible? The center of mass of the coin undergoes circular motion, yet the only forces that will ever be on the coin is the weight and normal force, which can never point in the centripetal direction. Thus, where am I going wrong?
 
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Never mind, there has to be friction pointing inward. I got it.
 
Allow me to continue the question.
Why does it go in circles, and not fall (by tilting) while the CM's trajectory is linear
and in the the original direction?

in other words, what's the mechanism that makes the coin change it's direction or turn once it started tilting?

thanks
 

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