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

[vibha_ganji]

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?

 

[anuttarasammyak]

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.

 

[PeroK]

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.