What Happens When The Applied Force Equals the Static Friction Force?

In summary: So after it starts moving, if the applied force is lessened to equal the kinetic frictional force, it would move with constant speed.In summary, when the applied force on an object exceeds the maximum static frictional force, the object begins to move with constant acceleration. Static friction is usually greater than kinetic friction, resulting in a significant acceleration. However, if the applied force is equal to the kinetic frictional force, the object will move with constant speed.
  • #1
vibha_ganji
19
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In my teacher’s notes, it said that when the applied force on an object equals the maximum static frictional force, the object begins to move at constant velocity. My question is if both the applied force and the frictional force cancel as they are equal in magnitude, what force accelerates the object from zero velocity to its constant velocity?
 
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  • #2
Usually kinetic friction constant is smaller than static friction constant.
Applied force which equals the maximum static frictional force - the kinetic frictional source
would accelerate the body.
After it starts moving if applied force is lessened to equal the kinetic frictional force, it would move with constant speed.
 
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  • #3
vibha_ganji said:
In my teacher’s notes, it said that when the applied force on an object equals the maximum static frictional force, the object begins to move at constant velocity. My question is if both the applied force and the frictional force cancel as they are equal in magnitude, what force accelerates the object from zero velocity to its constant velocity?
This doesn't sound right. It should be:

... when the applied force on an object exceeds the maximum static frictional force, the object begins to move with constant acceleration.

Note that static friction is usually greater than kinetic friction, so that you get a significant acceleration depending on how large this difference is. If the force is constant, then there is theoretically a minimum acceleration of ##\frac{f_s - f_k]{m}##, where ##f_k## is the kinetic friction, ##f_s## the static friction and ##m## the mass of the object. We assume that the applied force is approximately ##f_s## but just a tiny bit more.
 
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1. What is the definition of a static friction force?

The static friction force is a force that acts between two surfaces in contact with each other, preventing them from sliding against each other when at rest.

2. How is the static friction force calculated?

The static friction force is calculated by multiplying the coefficient of static friction (μs) between the two surfaces by the normal force (N) acting on the object.

3. What happens when the applied force equals the static friction force?

When the applied force equals the static friction force, the object will remain at rest and will not slide or move. This is because the static friction force is equal and opposite to the applied force, resulting in a net force of zero on the object.

4. Can the static friction force ever be greater than the applied force?

Yes, the static friction force can be greater than the applied force. This occurs when the applied force is not enough to overcome the maximum static friction force between the two surfaces, resulting in the object remaining at rest.

5. How does the coefficient of static friction affect the applied force and resulting motion?

The coefficient of static friction determines the maximum amount of static friction force that can be applied to an object before it starts to move. A higher coefficient of static friction means that a greater applied force is needed to overcome the static friction force and move the object.

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