When moving the plane forward speed it would clash with a strong air flow resistance. There is a garden to the rear direction trying to resist, the speed of the aircraft decreased.
When the plane moves forward, it will speed collision with a stream of air resistance. Is directed to the rear garden, try to resist the airspeed decreased.
When the plane moves with forward speed will clash with the air stream caused friction. The garden to the rear direction try resistant to the airspeed decreases.