Answer:
It is called force of friction
Explanation:
The force of friction is a force that acts between two objects whose surfaces are in contact with each other.
Consider the typical case of an object sliding along a certain surface. There are two types of frictions:
- Static friction: this is the force of friction that acts when the object is not in motion yet. If you push the object forward with a force F, the object will not move immediately, but it will "oppose" to this motion with a force of static friction exactly equal to the push applied:
[tex]F_f = F[/tex]
However, this force of static friction has a maximum value, which is given by
[tex]F_{max} = \mu_s N[/tex]
where
[tex]\mu_s[/tex] is the coefficient of static friction
N is the normal reaction exerted by the surface on the object
So, when [tex]F[/tex] becomes greater than [tex]F_{max}[/tex], the static friction is no longer able to balance the push applied, and the object will start sliding forward.
- Kinetic friction: this is the force of friction that acts when the object is already in motion. Its magnitude is given by
[tex]F_f = \mu_k N[/tex]
where
[tex]\mu_k[/tex] is the coefficient of kinetic friction, and its value is generally smaller than [tex]\mu_s[/tex]. The direction of this force is also opposite to the direction of motion of the object.
