B Why does a wall break and not move when pushed?

[Indie]

When there is a wall and a huge machine tried to move it and applied force on it at a point, why will the wall break at the spot the force is being applied and not move away?

 

[phinds]

When there is a wall and a huge machine tried to move it and applied force on it at a point, why will the wall break at the spot the force is being applied and not move away?

Well, think about it the other way 'round ... why would you expect it to move away? Under what conditions might it do so?

 

[Indie]

Well, think about it the other way 'round ... why would you expect it to move away? Under what conditions might it do so?

Well, in other cases it works so why not this one? Let's say there's an empty crate... If you exerted some force on it at a point, it will move away, not break at the point you are applying the force at, right?

 

[hilbert2]

How about increasing the area on which the force is applied?

 

[phinds]

Well, in other cases it works so why not this one? Let's say there's an empty crate... If you exerted some force on it at a point, it will move away, not break at the point you are applying the force at, right?

Sure. What's the difference between a crate and a wall?

 

[PeroK]

Well, in other cases it works so why not this one? Let's say there's an empty crate... If you exerted some force on it at a point, it will move away, not break at the point you are applying the force at, right?

If you hit a crate with a hammer, it might move or it might break.

 

[jbriggs444]

Sure. What's the difference between a crate and a wall?

Or, what difference is there in the design requirements?

 

[CWatters]

When there is a wall and a huge machine tried to move it and applied force on it at a point, why will the wall break at the spot the force is being applied and not move away?

Have a think about the top an bottom of a wall compared to a crate.

 

[pinball1970]

When there is a wall and a huge machine tried to move it and applied force on it at a point, why will the wall break at the spot the force is being applied and not move away?

The guys have hinted at it, If you had a similar weighted object similar length but instead of a wall it was a log, same force applied same what would happen? (Say it was cut in half from top to botton so could not roll, the surface on the floor was flat)

 

[russ_watters]

This is too painful to watch.

When there is a wall and a huge machine tried to move it and applied force on it at a point, why will the wall break at the spot the force is being applied and not move away?

Walls are attached to the ground!

 

[CWatters]

And usually the ceiling as well.

 

[phinds]

This is too painful to watch.

Walls are attached to the ground!

Spoilsport

Actually, I was beginning to wonder if we were being trolled.

 

[pinball1970]

I was going to mention tensile strength but no one seems to be really taking it seriously so... ok sometimes walls fall over

 

[sophiecentaur]

It's a battle between Mr Newton and Mr Hooke. If the forces are great enough, the material will distort. If they are not, the object will accelerate. It just depends - as in all Physics. the numbers count.

 

[Droidriven]

When there is a wall and a huge machine tried to move it and applied force on it at a point, why will the wall break at the spot the force is being applied and not move away?

Because a wall is typically in a fixed, anchored position, the entire wall is stronger than the surface area of the point of contact between the machine and the wall. The force applied exceeds the strength of the material at the contact point but does not exceed the combined strength of the rest of the wall. Thus, the path of least resistance for the moving object(the machine) is to break through at the contact point instead of pushing the whole wall.

That is for a fixed, anchored wall, it would be different if the wall were suspended touching nothing or resting in a standing position but not anchored/attached to anything, then the wall would move as long as the force applied exceeds any other possible resistances acting on the wall(gravity, friction, inertia, magnetic attraction, etc). If these resistances are greater than the force applied, the wall would break at the contact point the same as an anchored wall does, because these resistances would be its anchor.

 

[orzyszpon]

Indie is essentially right. I happen to have fixed the back wall of the garage that a relative of mine drove into. All kinds of damage ensued. The wall is a gypsum board attached by screws to vertical studs. The studs are attached at the top and the bottom to the top plate and bottom plate, respectively, with nails driven down from the top and the bottom. The bottom plate is attached to the concrete slab or to joists below.
When something like a car hits the wall, the drywall, of course, is history. If the nails hold, the stud may break. Since my relative hit the wall rather low, several studs were ripped off the bottom nails and swung away, hanging only from the top plate. Only those studs directly hit by the car were affected; the wall, as a whole, did not move.
As you can see, the fate of the wall depends on the strength of the wood and of the friction of the nails holding the studs, etc.

 

[kartikey]

on a brick of wall the various forces acting are normal reactions from all sides of wall except from the side you are applying force and its weight. Now when you aply force it will create a stress which will lead to inçrease in strain of the body according to hooke's law. so this will force th brichbrick and eventually the wall to break

 

[Uriah Graves]

1. The materials of your typical crate and typical drywall are vastly different. Thus, both are able to withstand different amounts of force.
2. The typical crate, when being acted on by a force, has only one obstacle to overcome before it moves position: frictional force. Typically, a crate's materials are strong enough to withstand an outside force, which allows the crate to overcome the frictional force before breaking, deforming, etc. (frictional force is the force occurs when two objects are in direct contact with one another [EX: a cube of steel on concreate has a downward force "W" which is it's mass*gravity and the concrete is exhibiting a normal force "N" on the cube of steel. this is Newton's 1st Law. Frictional force always opposes the motion of the force. So if I apply a force on the steel block parralel to the surface of the concrete that is great enough, I will overcome the friction between the two objects.)
3. A typical drywall is anchored/fixed at the top and bottom. It is not constructed to withstand large forces. Therefore, when a force is applied to it, it will not be able to overcome a frictional force before breaking, deforming, etc.

I'm no expert, but I think that It really comes down to the design, strength of materials, and whether or not it is fixed.

 

[Uriah Graves]

How about increasing the area on which the force is applied?

This could change things drastically.

 

[kartikey]

This could change things drastically.

if you increase area then stress will decrease as stress =force÷area
so you will need a larger force to break the wall

 

[jbriggs444]

if you increase area then stress will decrease as stress =force÷area
so you will need a larger force to break the wall

If you are breaking a beam that is supported on the ends by pushing in the middle, it does not matter greatly whether the force you apply is concentrated or dispersed. The highest stress will typically (*) occur not directly as pressure due to the applied normal force. Instead it will arise indirectly, from the resulting tension and compression in the beam.

In a wooden beam, the result could be a failure in tension as the fibers on the far side of the beam give way.

(*) If you use a sharp axe, the directly applied stress could indeed be significant.

 

[Nugatory]

Indeed, the total force acting on the wall is zero, but that's not because you are not applying a force, but because the wall reacts by applying the same exact force to balance yours.

That's not correct. The net force on the wall is zero, but the force that balances our pushing is not the wall reacting to being pushed, but rather the force of the ground (or whatever the wall is attached to) pushing n the wall.

 

[sophiecentaur]

That's not correct. The net force on the wall is zero, but the force that balances our pushing is not the wall reacting to being pushed, but rather the force of the ground (or whatever the wall is attached to) pushing n the wall.

If I had £1 for every time someone on PF confuses Newton's First and Third Laws, I could afford to take all the Science Advisors out for quite a few beers.