FBD Description

  • #1

Homework Statement


2z6bl8y.png


Describe a real situation that would give rise to the FBD of the block. N is normal, T is tension, W weight, f static friction

Homework Equations


Fnet = ma



The Attempt at a Solution


A block glued to a wall, while someone pulling a string down on it.
 

Answers and Replies

  • #2
SammyS
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Homework Statement


2z6bl8y.png


Describe a real situation that would give rise to the FBD of the block. N is normal, T is tension, W weight, f static friction

Homework Equations


Fnet = ma

The Attempt at a Solution


A block glued to a wall, while someone pulling a string down on it.
The glue's effect probably won't count as friction.

Where would the normal force come from ?
 
  • #3
The normal force would come from the surface, say a wall
 
  • #4
SammyS
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The normal force would come from the surface, say a wall

Under what condition(s) would the wall be exerting a horizontal force on the block ?
 
  • #5
If you push with a horizontal force, canceling the normal force. Problem is I don't think you can add your own force.
 
  • #6
SammyS
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If you push with a horizontal force, canceling the normal force. Problem is I don't think you can add your own force.
How about if the wall pushes with a constant force ? (In what direction would that have to be?)

What situation would require such a force? -- At least the magnitude of the force might be constant.
 
  • #7
Block at rest on a rough wall. Man pulls the string attached to block to balance with static friction?
 
  • #8
SammyS
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Block at rest on a rough wall. Man pulls the string attached to block to balance with static friction?
You need a normal force for there to be friction.

The normal force is generally a "reaction" force, so if the wall exerts a force of N (to the left) on the block, the block is exerting a force of magnitude N on the wall (to the right.)

It looks like there is only one horizontal force exerted on the block, namely N, which must be unbalanced if the magnitude of N is not zero. What would Newton say about that?
 
  • #9
Will accelerate in normal force's direction
 
  • #10
Person just lets go off block originally held by hand
 
  • #11
SammyS
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Person just lets go off block originally held by hand

Then there is no longer any normal force -- once the person lets go.
 
  • #12
SammyS
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  • #13
So what is an example of a real situation?
 
  • #14
SammyS
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So what is an example of a real situation?

It seems that you are to come up with the answer.
 
  • #15
Two blocks on table. Second block accelerating to left, exerting a normal force on first block. Person pulls down string on block.
 
  • #16
Anyone else willing to offer more tips/guidelines to solving this problem?
 
  • #17
PhanthomJay
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Anyone else willing to offer more tips/guidelines to solving this problem?
Think with imagination about a trip to Palisades Park.
 
  • #18
Man still not getting it... can someone please offer specific advice? I understand the principles. It must be accelerating to the left, but I can't think of a real life example.
 
  • #19
SammyS
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Think with imagination about a trip to Palisades Park.

Man still not getting it... can someone please offer specific advice? I understand the principles. It must be accelerating to the left, but I can't think of a real life example.

Wow!

Jay gave an excellent suggestion -- to think about (rides) at an amusement park.

Initially, you might not have the tension involved.
 
  • #20
How about a larger block (m3) moving to the left which exerts a normal force on m2. m2 is connected to m1 via a string. m2 and m1 have the right values so they do not move vertically; instead they move at the same acceleration as m3.
 

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