Time Flowing with Falling Stick

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SUMMARY

The discussion focuses on calculating the time it takes for a stick to fall under the influence of gravity, specifically addressing the torque involved in the motion. The center of mass of the stick is located at L/2, and the torque equation, Στ = Iα, is essential for solving the problem. The moment of inertia for a stick pivoted at one end is given by I = mL²/3. Understanding these concepts is crucial for accurately determining the time of fall.

PREREQUISITES
  • Understanding of basic physics concepts, particularly torque and angular momentum.
  • Familiarity with the equation of motion for rotational dynamics, specifically Στ = Iα.
  • Knowledge of the moment of inertia, especially for a uniform stick pivoted at one end.
  • Ability to draw free-body diagrams to visualize forces acting on the stick.
NEXT STEPS
  • Study the principles of torque and how it affects rotational motion.
  • Learn about angular momentum and its role in dynamics.
  • Explore the derivation and application of the moment of inertia for various shapes.
  • Practice solving problems involving free-body diagrams and rotational dynamics.
USEFUL FOR

Physics students, educators, and anyone interested in understanding the dynamics of falling objects and rotational motion.

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Mod note: deleted image that was way too large.[/color]

Homework Statement


I want to know the time flowed while the stick falls.

gravity = g
density of the stick is same so it's center of mass is l/2.
what is the T?

Homework Equations


The Attempt at a Solution


failed to do torque.
 
Last edited by a moderator:
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You mean - "how long does it take for the stick to fall?"
Is the point of contact a fixed pivot?

failed to do torque.
... then learn.
The subject requires an actual physics lesson - there is no shortcut - lessons are expensive for a reason.

You need to draw the forces into the diagram.
At the center of mass, gravity creates a torque.

Torque is the perpendicular component of the force times the distance.
In your case, the torque will depend on the angle.

The equation to solve is ##\sum\tau = I\ddot\theta## ... so you need to know about angular momentum as well. For the stick, pivoted about one end, ##I=mL^2/3## - where L is the length of the stick.
 

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