Acceleration: 

This video of the F-22 Raptor taking off demonstrates acceleration. A plane needs enough airflow over the wings to allow the plane to take off. Therefor, the two jet engines propels the aircraft forwards allowing it to gain speed. Acceleration is an increase in the rate of speed. The plane taking off clearly demonstrates the acceleration of the plane as it takes off.

Constant velocity: 

This video shows a commercial aircraft flying at a constant velocity. It does not change direction, or the speed. The autopilot system in the cockpit allows the plane to fly straight and level at the same airspeed for extended period of time.  Constant velocity is when n object stays in motion. It does not change direction or the speed of which the object is travelling at. This cruising Boeing 777 demonstrates constant velocity because it is travelling in one direction and constant speed.