introduce internal stresses

balance the other forces acting on it

retard its motion

all of the above.

if any number of forces acting at a point can be represented by the sidesof a polygon taken in order, then the forces are in equilibrium

if any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon, then the forces are in equilibrium

if a polygon representing forces acting at a point is closed then forces are in equilibrium

if any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon taken in order, then the forces are in equilibrium

magnitude

direction

position or line of action

all of the above

not a replace them by a single force

to replace them by a single force

to replace them by a single force through C.G.

to replace them by a couple

magnitude

direction

point of application

all of the above