Forces on Identical Bricks: Ranking Magnitudes

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Homework Help Overview

The discussion revolves around the forces acting on three identical bricks being pushed across a table at constant speed. Participants are examining the balance of forces, including push and friction, and how these relate to the motion of the bricks.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to understand how the bricks can continue moving if the push force equals the friction force, questioning the implications of this balance on motion.

Discussion Status

Some participants provide clarification on the relationship between the push force and friction, explaining that a balance allows for constant speed without acceleration. There is an acknowledgment of the principles of Newton's laws, but no explicit consensus has been reached.

Contextual Notes

Participants are discussing the implications of Newton's laws, particularly in the context of constant velocity motion and the conditions required for acceleration or deceleration.

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Three identical bricks are pushed across a table at constant speed as shown. Rank the magnitudes of all the horizontal forces that you identified in your free body diagram. So I identified the horizontal forces of push, friction, system a on system b, and b on a. I understand the force will equal 0 because they are moving at a constant speed and are equal and opposite. I am having trouble conceptualizing how if the force of the push is equal to the force of friction the blocks could possibly keep moving forever. If the force of the push equals the force of friction doesn't that mean it would stop moving because of friction??
 

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No, it means that there is a push force balancing the friction so that the object does not accelerate. In order to decelerate (slow down) an object there needs to be a net force on it according to Newton's second law and the friction would have to be larger than the push.
 
Orodruin said:
No, it means that there is a push force balancing the friction so that the object does not accelerate. In order to decelerate (slow down) an object there needs to be a net force on it according to Newton's second law and the friction would have to be larger than the push.

Oooooh that makes a lot of sense. Thanks a lot!
 
The answes lies in Newton's first law.
 

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