Understanding Friction: The Impact of Contact on Object Movement

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Discussion Overview

The discussion revolves around the concept of friction, particularly in the context of moving objects in contact with surfaces, such as a sofa against a wall. Participants explore the factors that influence the difficulty of pushing an object when it is in contact with another surface, considering both theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions why it is harder to push a sofa against a wall compared to when it is not touching the wall, initially attributing this to friction.
  • Another participant suggests that friction depends on the normal force, which is affected by the deformation of the sofa when in contact with the wall.
  • Concerns are raised about the concept of "real time force," with participants discussing the nature of normal forces and contact forces in the context of the sofa's compression against the wall.
  • Some participants propose that the amount of friction could be related to the degree of compression of the object, while others challenge this notion, stating that the relationship is not straightforward and depends on various parameters.
  • It is noted that the normal force is typically non-linear and influenced by material properties, which complicates the relationship between compression and friction.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between compression and friction, with some suggesting a proportionality while others argue against it. The discussion remains unresolved regarding the exact nature of these relationships and the factors at play.

Contextual Notes

Participants acknowledge that real-world scenarios may not conform to simplified models, and the discussion highlights the complexity of frictional forces, normal forces, and material properties.

Who May Find This Useful

This discussion may be of interest to those studying physics, particularly in the areas of mechanics and material science, as well as individuals curious about the practical implications of friction in everyday scenarios.

lekh2003
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I've just been thinking, and I don't know why I couldn't figure this out on my own, but I got this question bugging me.

I was moving a sofa the other day. The sofa was against a wall. I started thinking why it was harder to push the sofa parallel to the wall when it was touching the wall rather then when it was not touching the wall. I hope you see what I mean.

My initial thought was that there was friction against the wall, but then I thought mathematically. What would the friction be? I am not exerting any force on the sofa pushing it towards the wall, so why is there friction?

Why is it harder to push an object when it is simply in contact with the wall, even though there is no force to act on the object to generate friction?
 
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lekh2003 said:
My initial thought was that there was friction against the wall, but then I thought mathematically. What would the friction be?
Friction depends on the normal force. When you push the sofa against the wall, it deforms which requires a normal force.
 
A.T. said:
Friction depends on the normal force. When you push the sofa against the wall, it deforms which requires a normal force.
But there isn't a real time force. It's just like that, still. And then I apply a force completely perpendicular to the normal force for friction.

And what if it was a flat hard box with no deformation allowed? It would still be easier to push if it wasn't against the wall.
 
The sofa can have some force simply from having contact with the wall (and being compressed due to that), and you pushing the sofa might contribute as well.
The effect should be small unless you push it in a very odd direction.
 
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lekh2003 said:
But there isn't a real time force.
No idea what a "real time force" is. As long as parts of the sofa are compressed by the wall, there is a normal contact force between them.

lekh2003 said:
And what if it was a flat hard box with no deformation allowed?
There is no such thing in real life. But aside from the friction that depends on the normal force, you can have stickiness that opposes sliding with zero or even negative normal force.
 
A.T. said:
No idea what a "real time force" is. As long as parts of the sofa are compressed by the wall, there is a normal contact force between them.There is no such thing in real life. But aside from the friction that depends on the normal force, you can have stickiness that opposes sliding with zero or even negative normal force.
Ok so could i say that the amount of friction is proportional to the amount the object compresses. So a sofa might be harder to push than a box.
 
lekh2003 said:
Ok so could i say that the amount of friction is proportional to the amount the object compresses.
No, the normal force is usually non-linear.

lekh2003 said:
So a sofa might be harder to push than a box.
Depends on many parameters which might be different between the two.
 
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A.T. said:
No, the normal force is usually non-linear.Depends on many parameters which might be different between the two.
Ok not directly proportional, but as the compression is higher, the friction must also increase.

I think I got it. Thanks.
 
lekh2003 said:
Ok not directly proportional, but as the compression is higher, the friction must also increase.
Yes, but the normal force also depends on the material properties. And the friction then depends on the normal force and the surface properties.
 
  • #10
A.T. said:
Yes, but the normal force also depends on the material properties. And the friction then depends on the normal force and the surface properties.
Yes, I understand that. Thanks.
 

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