I saw a video on instagram where proffesor moves and throws a ball vertically, which means no force was given to ball horizontally, but weirdly(?) it also moves horizontally with the exact kinetic energy(I assume) that had professor moving horizontally. Can someone explain please why the ball moves horizontally, if no force/energy was given to ball horizontally?
Source: https://www.instagram.com/reel/C1b7jQegCVV/?igsh=cDhxNHU3b3hlYWJm
The ball originally had linear momentum in the horizontal direction which was due to the motion of the trolley horizontally. Since no force was applied in the horizontal direction, it's horizontal velocity stayed the same and it landed back on the trolley.
(By trolley I mean the cannon that was used to project the ball.)
The ball originally had linear momentum in the horizontal direction which was because to the motion of the cannon (that projected the ball) horizontally. Since no force was applied in the horizontal direction, it's horizontal momentum was conserved and it landed back on the Cannon.
I think it's quite important to look at this problem through the lens of relative motion, which may be unintuitive to some. Consider the trolley first. (Trolley referring to cannon.) It has a velocity, pointing in the horizontal direction. However, we must establish that this is not an absolute velocity, instead, it is relative to the motion of the Earth. Similarly, when the trolley and the golf ball initially started moving, they had no relative velocity with respect to each other. However, they both had the same relative velocity with respect to the Earth! Thus, when the golf ball is launched, it moves in the horizontal direction with respect to the Earth, and thus manages to land back again on the trolley!
I will end this answer with a thought question: Would this experiment provide the same results had there been air resistance?
