Why aren't forces N and G equal?

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Homework Help Overview

The discussion revolves around understanding the relationship between gravitational force and normal force acting on a block with a mass of 2kg on a frictionless horizontal plane. The original poster expresses confusion about why the normal force (FN) does not equal the gravitational force (FG), despite calculations suggesting a balance should exist.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the conditions under which normal and gravitational forces are equal, questioning the assumptions made about the forces acting on the block. There is discussion about the implications of zero vertical acceleration and whether the diagram provided is accurate.

Discussion Status

The conversation is ongoing, with participants sharing their interpretations and questioning the validity of the diagram from the program used. Some express uncertainty about their understanding of the forces involved, while others offer reassurance regarding the original poster's concerns about potential errors in the program.

Contextual Notes

Participants note that the program in question has a history of inaccuracies, which adds to the uncertainty regarding the forces depicted in the exercise. The original poster is also navigating the constraints of online learning, seeking real-time discussion and clarification.

leatherneckpa
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I am struggling with this one. The question is to explain why the gravitational and normal forces are not equal. And I'll be darned if I know why they aren't. Logic tells me they should be equal. The small block has a mass of 2kg. And multiplying that mass times the normal (9.8N) gives me the gravitational (19.6N). Unless the normal is a constant 9.8N per kg for ALL objects?

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Please describe the problem completely. What does that diagram show?
 
Did you make that diagram, or is it from other source?
 
The diagram is a portion of a screenshot from an exercise in a program called Interactive Physics. The horizontal plane is a frictionless plane. The small block is just a 2kg mass. FN is Normal force and reads 9.807N. FG is Gravitational force and reads 19.613N. FT is the applied force from the green arrow of 8N horizontal.

I'm supposed to explain why FN does not equal FG. But I thought they had to be balanced, hence equal?
 
leatherneckpa said:
I'm supposed to explain why FN does not equal FG. But I thought they had to be balanced, hence equal?
If the vertical acceleration of the block is zero, then the net vertical force must zero. Assuming that's the case here, that diagram looks incorrect.
 
Doc, there is no vertical acceleration. And so I figured I must be screwing something up. According my admittedly limited understanding FN should be equal to FG. If things were as the program is showing me it seems to me the block should be sinking downward (due to FG) in addition to moving to the right from the applied horizontal push.

There have been reports of this program screwing up in our online community. I just wanted to be sure the program was wrong and not me.
 
leatherneckpa said:
I just wanted to be sure the program was wrong and not me.
I don't think it's you. :wink:
 
OK, thanks.

Love this new resource too. Glad you guys are here. That's the only thing I have found so far that I don't like about online college, nobody to discuss things with in real time.

BTW, where's the link for the 20% discount on SciAm? I think I'd like to take advantage of that.
 

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