F = MA is Newton's second law. Force has english units of: foot-lbm/second^2 or just lbf; in SI units: Kilogram-meters/second^2 or just Newtons for short.
Momentum is Mass x Velocity and has units of foot-lbm/second or kilogram-meters/second.
So, a mass moving at a constant velocity does not exert a force. Only when the mass accelerates does it exert a force. For example when you're driving down the road at a constant speed you have momentum but you do not feel a force. However, if you accellerate you feel the equal and opposite force, another of Newtons laws, setting you back against the seat.