The free-body diagram looks like this:

Since the object does not move vertically, the vertical forces must
balance, so *n = W = mg =* (1 kg)(10 m/s^{2}) = 10 N.

__Case 1__. The force *F* has magnitude 5 N. The friction force
is limited and can be no greater than µ_{s}*n* = (0.75)(10
N) = 7.5 N. Thus the floor exerts a frictional force of magnitude 5 N,
the forces balance, and the object remains at rest. The acceleration is
zero.

__Case 2__. The force *F* has magnitude 8 N. This exceeds the
maximum of 7.5 N that the floor can exert, so the object begins to accelerate.
Once moving, the friction is kinetic, and we have *f = µ _{k}n
= *(0.6)(10 N) = 6 N. There is a net force of 8 N - 6 N = 2 N, and the
object's acceleration is