Horizontal Normal Force

In summary: It is just something that is true. It is fundamental that action and reaction are equal and opposite. I cannot think of a way to make it more intuitive. It is just something that is true.
  • #1
OrlandoLewis
25
1

Homework Statement


The two blocks (m=16kg and M=88kg) are not attached to each other. The coefficient of static friction between the blocks is us=0.38, but the surface beneath the larger block is frictionless. What is the minimum magnitude of the horizontal force F required to keep the smaller block from slipping down the larger block?
(I've attached the figure in this thread)

Homework Equations


Let F be the force applied and F' be the Force of the system
F = mg/[us(1-[m/(m+M)])]

The Attempt at a Solution


I already know the solution to the problem but I'm having a hard time seeing why the normal force of the smaller block is equal to the total force of the whole system, not to the force applied to the smaller block.
 

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  • #2
OrlandoLewis said:
the total force of the whole system,
I don't know what you mean by that.
Certainly the force applied is not equal to the he normal reaction from the larger block. If it were, there would be no net force on the smaller block, so no acceleration. If the smaller block is not accelerating then the larger block is not - or the two would separate. If no acceleration of the larger block then no net force on it. No net force on it implies no force from the smaller block.
 
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  • #3
haruspex said:
I don't know what you mean by that.
Certainly the force applied is not equal to the he normal reaction from the larger block. If it were, there would be no net force on the smaller block, so no acceleration. If the smaller block is not accelerating then the larger block is not - or the two would separate. If no acceleration of the larger block then no net force on it. No net force on it implies no force from the smaller block.

What I mean is the force of the two block combined which is equal to their total mass multiplied by the acceleration.
Why is it equal to the horizontal normal force to the smaller block?
 
  • #4
OrlandoLewis said:
What I mean is the force of the two block combined which is equal to their total mass multiplied by the acceleration.
Why is it equal to the horizontal normal force to the smaller block?
You are free to think of the two blocks as a single system. That system has an overall mass, all parts of it have the same horizontal acceleration, and there is just one external horizontal force acting on it. F=ma.
 
  • #5
OrlandoLewis said:
Why is it equal to the horizontal normal force to the smaller block?

The small block appears to only have two horizontal forces. If they are equal but opposite, what is the result?
 
  • #6
TomHart said:
The small block appears to only have two horizontal forces. If they are equal but opposite, what is the result?
I've attached here the free body diagram which yields the correct answer.
2016-08-29%2011.45.18.jpg

I doesn't really makes sense to me why the positive horizontal force F' is equal to the one horizontal force applied to the smaller block (negative direction).
 
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  • #7
OrlandoLewis said:
the positive horizontal force F' is equal to the one horizontal force applied to the smaller block (negative direction).
I don't understand what you mean by that. There are two forces applied to the smaller block, F and F'. F' is the reaction from the larger block, so is equal and opposite to the force on the larger block. F and F' are not equal.
 
  • #8
haruspex said:
I don't understand what you mean by that. There are two forces applied to the smaller block, F and F'. F' is the reaction from the larger block, so is equal and opposite to the force on the larger block. F and F' are not equal.
Sorry for not being to specific... I hope this'll get clearer.
My question is why is F' on the left (smaller block), the same as F' on the right (larger block)...
The intuition confuses me
 
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  • #9
OrlandoLewis said:
Sorry for not being to specific... I hope this'll get clearer.
My question is why is F' on the left (smaller block), the same as F' on the right (larger block)...
The intuition confuses me
It is fundamental that action and reaction are equal and opposite. I cannot think of a way to make it more intuitive.
 

What is horizontal normal force?

Horizontal normal force is a force that acts perpendicular to a surface, in a horizontal direction. It is also known as a lateral force or a shearing force.

How is horizontal normal force different from vertical normal force?

Horizontal normal force acts perpendicular to a surface in a horizontal direction, while vertical normal force acts perpendicular to a surface in a vertical direction.

What causes horizontal normal force?

Horizontal normal force is caused by the contact between two surfaces that are not parallel to each other.

How is horizontal normal force measured?

Horizontal normal force is measured in units of newtons (N) using a force meter or spring scale.

What is the significance of horizontal normal force?

Horizontal normal force is important in determining the stability and strength of a structure or object. It also plays a role in friction, which affects the movement of objects on a surface.

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