Static equilibrium marbles problem

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SUMMARY

The discussion centers on a static equilibrium problem involving two uniform 75g marbles stacked in a 3cm wide container. The participants analyze the forces exerted at points A, B, and C, where point A is the left contact point of the bottom marble, point B is the bottom contact point, and point C is the contact point of the top marble with the container. The key equations include the normal force at point B, which equals the combined weight of the marbles, and the torque calculation for the top marble on the bottom marble, expressed as weight*(0.01m)*(sin(30)). The importance of selecting an appropriate pivot point for torque calculations is emphasized.

PREREQUISITES
  • Understanding of static equilibrium principles
  • Knowledge of torque calculations, specifically T=sin(phi)*lever arm
  • Familiarity with forces acting on objects in contact
  • Basic physics concepts related to weight and normal force
NEXT STEPS
  • Study the concept of static equilibrium in-depth, focusing on force and torque balance
  • Learn about pivot points in torque calculations and their significance
  • Explore the effects of friction in static equilibrium problems
  • Practice similar problems involving multiple objects in static equilibrium
USEFUL FOR

Students studying physics, particularly those tackling static equilibrium problems, as well as educators looking for examples to illustrate torque and force interactions in stacked objects.

krko
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Hey all, new member here

Homework Statement


Two uniform 75g marbles 2cm in diameter are stacked on top of each other in a container that is 3cm wide
the top marble touches right side of the container, the bottom touches the left side.
Point A is the bottom marble left contact point with the container, point B is the bottom marble touch the bottom of the container, point c is the top marble's contact point with the container

Attempt at a figure:
l top marble, point Cl
lmarble contact pointl
lpoint A, bottom marble l
l_____point B________l
What is the force the container exerts at point A,B, and C?
What force does each marble exert on each other?

Homework Equations


Basically since its static equilibrium, , all force and torques add up to zero. Also the equation for Torque, T=sin(phi)*lever arm

The Attempt at a Solution



force at B is easy to get since that's just the normal force equal to the combined weight of the two marbles.
At A and C, its obvious that they're equal. I can also get the torque due to the top marble on the bottome marble: weight*(.01m)*(sin(30)) after that I don't know what else to do.
 
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Welcome to PF!

Hey, krko ! Welcome to PF! :smile:
krko said:
… I can also get the torque due to the top marble on the bottome marble: weight*(.01m)*(sin(30)) after that I don't know what else to do.

Is this frictionless?

You're taking moments about the point of contact between the marbles … why? :confused:

If you take moments (torques) about a point, you must do it for all the forces … that's why we usually choose a point about which some of the forces have zero moment.

Try again, taking moments about a different point. :smile:
 
Okay, i uploaded an image of the problem. The torque I'm talking about is the torque caused by the top marble about point the center of the bottom marble. Although looking back i think I found my mistake, that I neglected the effect of the force of the container on point C on the bottom marble.
 

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