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Lecture Comments (2)

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Post by Marcos Castillo on April 27, 2014

Hi, Professor Jishi. I am trying to understand something you might be very helpful: let's suppose an arch made out whith three blocks: the keystone and two springers. The arch is in static equilibrium over the ground; let's suppose there is no friction between the keystone and the springers, but there is friction between ground and the springers, so that the arch stands up. Which is the description of the net torque on one of the springers?. I know that the forces exerted on the springer are: force exerted by the keystone on the springer, with its vertical and horizontal components; the friction; the weight of the springer; and the normal force.
I've tried hard to solve, and I've asked some other places, with no results. About which point should I define the net torque?. How can I conclude the net torque is zero?.
Thank you very much!

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Post by Juan Zavala on May 1, 2013

Please don't, I enjoy your pase. It aids me in better understanding the material because I have time to fully comprehend your lesson.

Static Equilibrium

  • A force, applied to a body at a given point, produces a torque about another point O. The magnitude of the torque about O is equal to the product of the force and the perpendicular distance of the force from O.
  • A body is in static equilibrium if (a) the net force on the body is zero, and (b) the net torque on the body is zero.
  • In solving problems on static equilibrium, simplification is obtained if a judicious choice is made of the point O, about which torques are calculated.

Static Equilibrium

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Torque 0:09
    • Introduction to Torque
    • Rod in X-Y Direction
  • Particle in Equilibrium 18:15
    • Particle in Equilibrium, Net Force=0
    • Extended Object Like a Rod
    • Conditions of Equilibrium
    • Forces Acting on Object (Proof of Torque)
  • The Lever 35:38
    • Rod on Lever with Two Masses
  • Standing on a Supported Beam 40:53
    • Example : Wall and Beam Rope Connect Beam and Wall
    • Net Force
    • Net Torque
    • Finding ø
  • Ladder About to Slip 53:38
    • Example: Finding Angle ø Where Ladder Doesn't slip
  • Extra Example 1: Bear Retrieving Basket
  • Extra Example 2: Sliding Cabinet