Physics forces question

[Maxine450]

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I forgot where I read this but it's been bothering me

When hammering a nail in the wall, it gets harder to force in the nail the deeper it goes? Why? What forces increase as you hammer in the nail?

I think friction was one of the choices but I cannot remember. Any ideas?

 

[MedPR]

I forgot where I read this but it's been bothering me

When hammering a nail in the wall, it gets harder to force in the nail the deeper it goes? Why? What forces increase as you hammer in the nail?

I think friction was one of the choices but I cannot remember. Any ideas?

Idk, but from experience the hardest part of hammering in a nail is the very beginning.

 

[chiddler]

Idk, but from experience the hardest part of hammering in a nail is the very beginning.

That's because you can't apply as much force since you have to orient the nail correctly.

But as it goes further inside, more nail surface is in contact with medium surface. So friction force increases.

Sounds right. Is this right?

Maybe pressure has something to do with it as well, since the tip of the nail is no longer the only part that is being forced, but the entire cone shape at the end. This is more area and thus more pressure has to be applied.

 

[pfaction]

I was thinking friction, because the distance is also increasing. I don't think it's pressure but I don't know.

 

[theseeker4]

I forgot where I read this but it's been bothering me

When hammering a nail in the wall, it gets harder to force in the nail the deeper it goes? Why? What forces increase as you hammer in the nail?

I think friction was one of the choices but I cannot remember. Any ideas?

I would vote for friction. Pressure and the like doesn't make as much sense.

 

[MedPR]

Except we know that friction is independent of how much of the object is in contact with the friction-creating-surface.

E.g if you have a 10x5 block with mass 50kg, the frictional force is the same whether you lay the block on its 10m side or on its 5m side. That's why I didn't want to say friction was the answer.

Edit: I'm going to guess that as more nail is in contact with wood (as it gets deeper), more and more of the kinetic energy from the hammering is dissipated as heat energy since more of the nail is in contact with the wood and wood has a higher heat capacity (than air) so it has a greater ability to absorb heat energy.

 

[chiddler]

Why are nails easier to pull out when they are closer to the surface?

 

[milski]

Except we know that friction is independent of how much of the object is in contact with the friction-creating-surface.

E.g if you have a 10x5 block with mass 50kg, the frictional force is the same whether you lay the block on its 10m side or on its 5m side. That's why I didn't want to say friction was the answer.

Edit: I'm going to guess that as more nail is in contact with wood (as it gets deeper), more and more of the kinetic energy from the hammering is dissipated as heat energy since more of the nail is in contact with the wood and wood has a higher heat capacity (than air) so it has a greater ability to absorb heat energy.

That's true only if the normal force stays the same. For the nail, the normal increases as the nail goes deeper.

Your edit is just a roundabout way of saying that there is more friction - that's how kinetic energy is converted to heat.

All this is applicable to an ideal nail, which will have uniform pressure distribution from the wood. If the nail is not completely cylindrical, only the parts to its widest portion will have pressure from the wood. After the widest part is in, the pressure will be practically constant.

 

[milski]

Why are nails easier to pull out when they are closer to the surface?

Less normal force from the wood -> less friction.

For a non-ideal nail which has a slightly wider part, once the widest cross-section is out there will be almost no friction. And most real world nails are non-ideal. 😉

 

[MedPR]

Why does normal increase as the nail goes deeper?

 

[milski]

Why does normal increase as the nail goes deeper?

A few ways to think about it. The further in, the more wood is deformed. You can treat as pressure or a lot of tiny springs - the end result is the same.


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[MedPR]

A few ways to think about it. The further in, the more wood is deformed. You can treat as pressure or a lot of tiny springs - the end result is the same.


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Ah, I didn't think about that. Thanks 🙂

 

[Maxine450]

But the mass is the same...how could the normal increase? Because the nail is becoming "part of" the wood?

I think there was a similar question next to it. "Why does a sharp knife cut easier than a dull one?"

I was thinking about pressure, because a sharp knife has a very small area with a lot of force, a dull knife has a wider area with the same pressure, so there's less force. But pressure wasn't among the answers. Is it friction?

 

[chiddler]

But the mass is the same...how could the normal increase? Because the nail is becoming "part of" the wood?

I think there was a similar question next to it. "Why does a sharp knife cut easier than a dull one?"

I was thinking about pressure, because a sharp knife has a very small area with a lot of force, a dull knife has a wider area with the same pressure, so there's less force. But pressure wasn't among the answers. Is it friction?

that is definitely pressure.

a sharp knife has less area on its cutting side and thus more pressure.

 

[phyguy719]

I forgot where I read this but it's been bothering me

When hammering a nail in the wall, it gets harder to force in the nail the deeper it goes? Why? What forces increase as you hammer in the nail?

I think friction was one of the choices but I cannot remember. Any ideas?

The answer is and isn't pressure. As the nail is driven, the surface area in contact with the wood increases at the same rate as the force applied(by the wood), so pressure actually stays the same. But remember, frictional forces are dependent on the magnitude of force, not the magnitude of pressure. In theory, a triangular shape resting on a surface will have the same friction force whether it rests on a point (high pressure), or on one of the sides (low pressure), because the normal force is same in both cases. But for the nail, as the surface area in contact with the wood increases (linearly), the normal forces (not the pressure) will increase linearly as well. This is also why a thin nail is easier to drive then a thick nail. The pressure is the same for both cases but the thick nail has more surface and therefore higher forces.