Do you consider both regular and rotational kinetic energy?

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SUMMARY

The discussion centers on the consideration of both translational kinetic energy and rotational kinetic energy for objects in circular motion, specifically a ball attached to a string. The kinetic energy is calculated using the formula (1/2)mv², while the rotational kinetic energy is calculated using (1/2)Iω². It is established that in scenarios where the radius of the ball is significantly smaller than the radius of the circular path, the rotational kinetic energy can be neglected, allowing the ball to be treated as a point particle. This simplification is common in physics problems involving circular motion.

PREREQUISITES
  • Understanding of kinetic energy formulas: (1/2)mv² and (1/2)Iω²
  • Basic knowledge of rotational dynamics and moment of inertia (I)
  • Familiarity with circular motion concepts
  • Ability to differentiate between translational and rotational motion
NEXT STEPS
  • Study the implications of neglecting rotational kinetic energy in various physics problems
  • Explore the concept of moment of inertia and its calculation for different shapes
  • Learn about the dynamics of objects in circular motion, including centripetal force
  • Investigate real-world applications of rotational and translational kinetic energy in engineering
USEFUL FOR

Students of physics, educators teaching mechanics, and engineers involved in motion analysis will benefit from this discussion.

fangrz
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Homework Statement


If I have a ball moving in a circular path (ball is connected to a string), as shown in this picture:
http://w3.shorecrest.org/~Lisa_Peck.../circularmotion/Images/cent_force_on_ball.gif

should I say that the energy of the ball is both its kinetic energy (1/2)mv^2 and its rotational kinetic energy = (1/2)Iomega^2?

Homework Equations


kinetic energy (1/2)mv^2
rotational kinetic energy = (1/2)Iomega^2

The Attempt at a Solution


I was just thinking about this. I mean, what if you have a car moving in a circle--do you consider both kinetic energy and rotational kinetic energy?
 
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Hello fangrz.

In principle, the total kinetic energy would include rotational KE as well as translational KE. However, if the radius R of the ball is much less than the radius r of the circle, then the rotational KE is very small compared to the translational KE. You can easily check this. So, the rotational KE is often neglected in this type of situation. Then the ball is effectively treated as a "point particle".
 
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