Force applied on suspending/falling mass

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SUMMARY

The discussion focuses on the effects of applied forces and torques on a falling rod and a flipping car. When a horizontal force is applied to a falling rod, it creates a torque about an axis that is not necessarily at the center of mass. The axis of rotation for a body in motion, such as a flipping car, does not always pass through its center of gravity. The net torque can be calculated using the relationship torque = moment of inertia times angular acceleration, similar to linear dynamics.

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  • Understanding of torque and moment of inertia
  • Familiarity with Newton's laws of motion
  • Basic knowledge of rotational dynamics
  • Concept of center of mass in rigid body motion
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  • Study the principles of rotational dynamics in detail
  • Learn about calculating torque in various scenarios
  • Explore the concept of the instant center of rotation
  • Investigate methods for integrating angular motion over time
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Physics students, mechanical engineers, and anyone interested in understanding the dynamics of rotating bodies and the effects of applied forces on motion.

jakesee
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Hi,

May I ask, if there is a sufficiently long rod falling vertically downwards due to gravity, and then at an instance, a horizontal force is applied at one end of the rod, will this force create a torque on the rod? If so, where is the axis of rotation?

Second question, if a body, not hinged, is experiencing rotation, e.g. a flipping car in "mid air" in a collision, does the axis of rotation ALWAYS go through its center of gravity. If not, how do we find out which axis?.

Third question, say, in the flipping car example, is the "Net Torque" about any axis independent of any other axis? Is there a method to calculate the "net rotation about net axis" so that we can integrate over time to get the resultant orientation? Similar to integrating velocity vector to get position vector kind of maths?


Sorry, that's aquite abit. Hope I can get some help. Thanks for helping.
 
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Hi jakesee! :smile:

Yes, if there's a torque (a moment) about the centre of mass, then the body will rotate.

The position of the axis of rotation depends on the exact figures (it won't usually be the centre of mass).

The total angle of rotation doesn't depend on the axis. You can get the dynamics from torque = moment of inertia times angular acceleration, just like the linear F = ma.

See http://en.wikipedia.org/wiki/Instant_centre_of_rotation" for some details. :wink:
 
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Thanks for the replies, I'll be reading the suggested topics a while before coming back. thanks thanks. =)
 

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