Why is the system not considered isolated in this scenario?

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Homework Help Overview

The discussion revolves around the classification of a system as isolated or non-isolated in the context of forces acting on a block. Participants are examining the implications of external forces, particularly friction and gravity, on the block's motion.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the definition of an isolated system and discussing the forces acting on the block, including friction and gravity. There is confusion regarding the correct classification of the system based on these forces.

Discussion Status

Some participants have provided reasoning for why the system is considered non-isolated, citing the effects of gravity and friction. Others express confusion and seek further clarification on the correct answer, indicating that multiple interpretations are being explored.

Contextual Notes

There is mention of differing answers from various sources, which adds to the confusion regarding the classification of the system. Participants are also considering the implications of defining the system to include both the block and the surface.

jack1234
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For the following question, the answer given is b. Non-Isolated

http://tinyurl.com/2s3waq

But may I know why it is not a. Isolated?
 
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If is non-isolated, it certainly can't be isolated.

What forces are acting on the block?
 
Astronuc said:
What forces are acting on the block?

One of them is friction force, the other one not sure...

By the way, from the other sources, I found the answer is a, I am really confused now, what is the correct answer??
 
Hmm, can anybody shed me some light?
 
The correct answer is non-isolated, because the block is affected by gravity which acts on the mass of the block giving it weight. In turn, friction is an external force related to the weight.

On a horizontal surface, the only way the block could be moving is to have had an external force applied to it. If the driving force has been removed, it must be decelerating due to friction.

The forces are not internal to the block.
 
Last edited:
If the "system" had been the block and[\b] the surface, then the system would be isolated (since the surface is horizontal, gravity only acts to affect friction so doesn't have to be considered as a separate force).
 

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