I may be a masochist, but I will weigh in here;
When you throw the jar, you are accelerating it. Making it go faster and faster until you release it. (the same if it were a rocket and the engine cuts off)
Ignoring the friction of the air, the jar is now traveling through the air, with only gravity affecting it. As gravity is affecting the jar, the air inside it, and the seed equally; As it falls, the seed and air will experience zero G or weightlessness. Until the jar hits the ground. If you were looking at the jar with a pair of binoculars, you would see the seed is indeed moving at the same speed as the jar. But if you had a television camera in the jar, you would see the seed floating in mid air, seemly motionless.
As far as the ball in the airplane and the orange juice pouring out, you would see the same thing. Since the airplane is not falling, (ignoring the difference in the magnitude of G in the air as compared with ground level)gravity affects the ball and orange juice the same as being on the ground, as long as there is no acceleration in any vector. (It is moving smoothly through the air at a constant speed)
If the airplane were Wonder Woman’s and you could see the inside with binoculars, you would see the orange juice pitcher, the cup and the orange juice (and the ball) moving along with the airplane. If there were a television camera, it would look the same as if the airplane were on the runway on the ground.
I know I am going to regret posting these videos as they will be misinterpreted almost surely…
Doppler:
I included the doppler because he is going to not understand how if the ball is going 300 mph + the thrown velocity, why is it not the same for light.