FBD of Block: Real-Life Example and Equations

[tmobilerocks]

Homework Statement

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.

 

[SammyS]

Homework Statement

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 ?

 

[tmobilerocks]

The normal force would come from the surface, say a wall

 

[SammyS]

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 ?

 

[tmobilerocks]

If you push with a horizontal force, canceling the normal force. Problem is I don't think you can add your own force.

 

[SammyS]

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.

 

[tmobilerocks]

Block at rest on a rough wall. Man pulls the string attached to block to balance with static friction?

 

[SammyS]

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?

 

[tmobilerocks]

Will accelerate in normal force's direction

 

[tmobilerocks]

Person just let's go off block originally held by hand

 

[SammyS]

Person just let's go off block originally held by hand

Then there is no longer any normal force -- once the person let's go.

 

[SammyS]

Will accelerate in normal force's direction

Yes.

 

[tmobilerocks]

So what is an example of a real situation?

 

[SammyS]

So what is an example of a real situation?

It seems that you are to come up with the answer.

 

[tmobilerocks]

Two blocks on table. Second block accelerating to left, exerting a normal force on first block. Person pulls down string on block.

 

[tmobilerocks]

Anyone else willing to offer more tips/guidelines to solving this problem?

 

[PhanthomJay]

Anyone else willing to offer more tips/guidelines to solving this problem?

Think with imagination about a trip to Palisades Park.

 

[tmobilerocks]

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.

 

[SammyS]

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.

 

[tmobilerocks]

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.