Forces: mass on a string circular motion

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SUMMARY

The discussion centers on the forces acting on a mass attached to a string during circular motion. The resultant force on the mass is directed inward towards the center of rotation, known as centripetal force, due to the tension in the string. Conversely, an observer on the mass experiences an outward force, referred to as centrifugal force, which is a fictitious force perceived in a non-inertial frame of reference. Understanding these concepts requires recognizing the distinction between inertial and non-inertial frames when analyzing circular motion.

PREREQUISITES
  • Understanding of centripetal force and its role in circular motion
  • Familiarity with inertial and non-inertial reference frames
  • Basic knowledge of Newton's laws of motion
  • Concept of fictitious forces in physics
NEXT STEPS
  • Research the mathematical formulation of centripetal force in circular motion
  • Explore the concept of fictitious forces in non-inertial frames
  • Study examples of circular motion in different reference frames
  • Learn about the applications of centripetal force in real-world scenarios, such as roller coasters
USEFUL FOR

Students of physics, educators explaining circular motion concepts, and anyone interested in understanding the dynamics of forces in rotating systems.

climbon
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Hi, if I have a mass on a string and I swing it around my head at a constant speed, what is the resultant force on the mass (I'm looking for a qualitative rather than quantitive answer)?

My inital thoughts were towards the centre of rotation, due to the tension on the string (and since the mass is accelerating towards centre). So there must be a resulting force towards the centre?

But also if I was to sit on the mass I would feel an outward force, so I'm not quite sure??

Thanks for any help :)
 
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Yes, you feel an outward pull (the "centrifugal" force) due to the "equal and opposite" rule. You are applying an inward pull to the string and that feels to you like the same force outward. The force on the mass is inward, the force on you is outward.
 
climbon said:
Hi, if I have a mass on a string and I swing it around my head at a constant speed, what is the resultant force on the mass (I'm looking for a qualitative rather than quantitive answer)?

It depends on the reference frame you choose. The most common are (1) a fixed inertial frame observing the circular motion and (2) a non-inertial accelerating frame such as your mass at the end of the string. You've already recognized both.

My inital thoughts were towards the centre of rotation, due to the tension on the string (and since the mass is accelerating towards centre). So there must be a resulting force towards the centre?

Exactly. This is an example of observing the circular motion from an inertial frame (you). The mass accelerates inward towards a central point due to centripetal force. The balancing reactionary force outwards is centrifugal.

But also if I was to sit on the mass I would feel an outward force, so I'm not quite sure??

And that's the second example, when viewed from the non-inertial accelerating frame (the mass). Here the fictitious force you feel is centrifugal. The use of the term centrifugal is distinct from the first example, IOW different when used for the inertial frame #1 and the non-inertial frame #2.

I hope I got this mostly right :biggrin: and it helps!
 

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