Friction force and constant velocity

In summary: No, it is not. "viscosity" is more like the "coefficient of friction" that determines the force than the force itself.
  • #1
m_wu
2
0
Does the speed of a block of wood being pulled across a surface go twice as fast if you pull twice as hard? If yes/no, why?

Thanks to anyone who will answer that!
 
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  • #2
The net (horizontal) force on the block will determine the block's acceleration, the rate at which its speed changes. If you double the net force, the acceleration is doubled. You need more info to find the speed, since it changes.

If the net force is zero, the speed will remain constant.
 
  • #3
Would the force of friction double if you double the constant velocity of the wooden block? If yes, why?

Thank you again.
 
  • #4
Would the force of friction double if you double the constant velocity of the wooden block?

No. It requires more force to accelerate up to high speed, but once at high speed, the force needed to maintain that speed is the same as the force needed to maintain a lower speed. Subjectively (I mean if you are using your own muscles to do the pushing), it feels harder to go faster, but that is because the power expended is higher. Power = Force times speed, so you get tired faster.
 
  • #5
Originally posted by m_wu
Would the force of friction double if you double the constant velocity of the wooden block?
In the simplified freshman physics model, no. The kinetic friction is independent of velocity. In the real world, if you're just talking surface contact, I would imagine that the friction would actually decrease with velocity.
 
  • #6
Fluid friction depends strongly on velocity. Normal sliding friction usually doesn't depend on velocity much at all.
 
  • #7
Originally posted by Stingray
Fluid friction
By this, do you mean "viscosity" or something else. I've heard an old man call "viscosity" "pipe friction" (and then an argument ensued. Arguing with old men can be quite frustrating if you care to convence them).
 
  • #8
I meant viscosity as well as what would more precisely be called "pressure or inertial drag" (the main component of aerodynamic drag that's due to fluid being forced out of the way from an oncoming object).
 
  • #9
Originally posted by Stingray
I meant viscosity as well as what would more precisely be called "pressure or inertial drag" (the main component of aerodynamic drag that's due to fluid being forced out of the way from an oncoming object).
I didn't think this was the same thing as viscosity, but is was imprecise for me to say "viscosity" for force, when it is a coefficient, not a force. I thought that there could be drag without viscosity, though.
 
  • #10
Yes, you're right. My "as well as" meant that I was mentioning two different things.

I think it is common practice to call a force viscosity, isn't it?
 
  • #11
Originally posted by Stingray
Yes, you're right. My "as well as" meant that I was mentioning two different things.
Oh. I misunderstood. Sorry.




Originally posted by Stingray
I think it is common practice to call a force viscosity, isn't it?
I don't know. I don't ever talk about fluid dynamics with anyone. My first year phys book speaks of viscosity as a coefficient, an makes a point of not calling it a force.
 
  • #12
A 1 ounce marble pulled by a connected string with your hand moving at 1 mph will go no faster or slower than the same marble pulled by an 80 ton hydraulic jack whoes piston moves at 1 mph.
 
  • #13
The acceleration TO the 1 mph speed is much greater with the 80 ton hydraulic jack, however.
 
  • #14
By this, do you mean "viscosity" or something else. I've heard an old man call "viscosity" "pipe friction" (and then an argument ensued. Arguing with old men can be quite frustrating if you care to convence them).

Especially if they are right! "Pipe friction" doesn't cover everything, but it's a good off-the-cuff representation.

I think it is common practice to call a force viscosity, isn't it?

No, it is not. "viscosity" is more like the "coefficient of friction" that determines the force than the force itself.
 
  • #15
Originally posted by HallsofIvy
Especially if they are right! "Pipe friction" doesn't cover everything, but it's a good off-the-cuff representation.
I was trying to explain to him that my "viscosity" was his "pipe friction." It was a disaster. He just wasn't havin' any of that newfangled technical jargon.
 

1. What is friction force and how does it affect motion?

Friction force is the resistance force that occurs when two surfaces are in contact with each other. It acts against the direction of motion and can slow down or stop an object's movement.

2. How is the magnitude of friction force determined?

The magnitude of friction force is determined by the force pressing the two surfaces together and the coefficient of friction, which is a measure of how easily the surfaces slide against each other.

3. How does friction force change with constant velocity?

With constant velocity, the friction force remains constant as long as the surfaces and other conditions remain the same. This is because the force of friction is equal and opposite to the force applied to keep the object moving at a constant speed.

4. Can friction force be eliminated?

No, friction force cannot be eliminated completely. It can be reduced by using lubricants or by using smoother surfaces, but there will always be some degree of friction between two surfaces in contact with each other.

5. How does friction force vary with different surfaces?

The coefficient of friction varies with different surfaces, which means that the force of friction will also vary. For example, surfaces with a higher coefficient of friction, such as rubber on concrete, will have a higher friction force compared to surfaces with a lower coefficient of friction, such as ice on ice.

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