Maximal static friction problem

In summary, the question discussed the concept of minimum force needed to move a stationary object, which is equal to the maximum static friction force. However, the question posed a scenario with a sloped surface and an object moving upwards, causing confusion about the minimal static friction constant needed for the object to remain stationary. Newton's first law states that an object at rest will remain at rest unless acted upon by an external force, leading to the conclusion that the force needed to keep the object from moving should be greater than the maximum static friction force. However, the book used by the individual states that the minimal force needed to cause relative movement between two bodies in contact is equal to the maximum static friction force. There is a discrepancy between this statement and Newton
  • #1
Black Riven
4
0
This is mostly a theoretical question, I'm studying mechanics by myself so I have no teacher to ask this.

Homework Statement



The minimum force needed to move a stationary object is equal to the max static friction. However, I just encountered a question that included a sloped surface and an object moving upwards across it.

Eventually, mgcos(a)+Fk bring it to a halt, and the question is what should the minimal static friction constant be in order for the object to remain stationary.

The Attempt at a Solution



Fs must be strong enough to hold out against mgcos(a). The equation we are supposed to have is Fs-mgcos(a)=0
However, this confuses me. If when a force applied on the object equals to Fs(max) it causes it to move, Shouldn't the force needed to keep the object from moving be Fs>mgcos(a)?

In other words, is Fs(max) the breaking point or the last point before movement occurs?
 
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  • #2
It sounds like the question should read "minimal static friction constant"
 
  • #3
Black Riven said:
The minimum force needed to move a stationary object is equal to the max static friction.
Assuming a level surface, why do you say "equal to"? If an object is at rest and the max static friction force available is 20N and you push on it with a 20N force, will it move?
Eventually, mgcos(a)+Fk bring it to a halt, and the question is what should the minimal kinetic friction constant be in order for the object to remain stationary.
As noted above, change the word 'kinetic' to 'static'.
If when a force applied on the object equals to Fs(max) it causes it to move,
does it?
Shouldn't the force needed to keep the object from moving be Fs>mgcos(a)?
What does Newton's first law tell you?
 
  • #4
PhanthomJay said:
Assuming a level surface, why do you say "equal to"? If an object is at rest and the max static friction force available is 20N and you push on it with a 20N force, will it move?
This is the problem then. My intuition tells me that no, it will not move because the force must be bigger than Fs(max). However, the book I'm using says
The minimal force which causes relative movement between two bodies that share contact equals to the maximal static friction
Based on your answer I assume my intuition is correct? If Fs(max)=F the object will not move, and the minute F>Fs(max) it will start moving.
If that's the case any idea why the book says what it does?
PhanthomJay said:
As noted above, change the word 'kinetic' to 'static'.
Done.
 
  • #5
I think it's just saying that if the max static friction force is 20.000000000N, a force of 20.000000001N will, in theory, cause it to move. Close enough to 20, I guess.
 

FAQ: Maximal static friction problem

What is maximal static friction?

Maximal static friction is the maximum amount of frictional force that can be exerted between two surfaces in contact before one starts to move in relation to the other.

How is maximal static friction calculated?

Maximal static friction is calculated using the coefficient of static friction (μs) and the normal force (N) between two surfaces. The formula is Fmax = μsN, where Fmax is the maximal static friction force.

What factors affect maximal static friction?

The coefficient of static friction and the normal force are the two main factors that affect maximal static friction. Other factors that can influence it include the roughness of the surfaces, the presence of any lubricants, and the temperature.

What happens if the applied force exceeds the maximal static friction?

If the applied force exceeds the maximal static friction, then the object will start to move in relation to the other surface. This is known as kinetic friction, which is typically lower than maximal static friction.

How is maximal static friction important in everyday life?

Maximal static friction plays a crucial role in everyday life by allowing us to walk, drive, and hold objects without them sliding or slipping. It also helps to prevent accidents, such as car crashes and falls, by providing the necessary friction for objects to remain in place.

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