What forces are in speeding up?

Speeding up involves the net force acting on an object, which is the combination of all forces applied to it. According to Newton's second law of motion, if the net force in the direction of motion is greater than any opposing forces (like friction or drag), the object will accelerate. The force responsible for this acceleration can be due to gravity, engines, or other external influences. Essentially, the net force must be in the same direction as the object's motion to increase its speed.