Gravity, friction, and air resistance are some examples.
Understanding Newtons second law that everything has an equal and opposite reaction. The reaction force from a balloons air being pushed out is the preasurized air it had to push out into the open air.
Net force = (mass) x (acceleration)... that’s Newton’s 2nd law of motion.
Net force = (15kg) x (10 m/s squared)
Net force = 150 Newtons.