aerodynamicseducationkinematics
There is kind of toy "Helicone" (https://www.youtube.com/watch?v=nkmBLPHGp0E), It is composited with one base, one axle and many co-axle leaf-pairs.
When rotating it in a direction and suddenly stops, the angle of all leaves will be concentrated.
However, if rotating it in the opposite direction, all the leaves will distributed uniformly among all the angles.
The toy is made with pure wood except the axle.
Why it can achieve such effect? What is the physics principle behind it?
You are absolutely correct that the change in direction of the tennis ball is due to the difference in pressure on the top and bottom of the ball. Below is an example of a top-spin shot with the ball traveling from left to right.
The speed of the air passing the ball on the top is slower than on the bottom of the ball. You can see this by summing the blue and yellow arrows on the top and bottom of the ball. Since faster flow creates lower pressure, there will be a pressure difference between the top and bottom of the ball, with high pressure on top and low on bottom. This will force the ball to the right of its motion (down in this example).
Here you can see the streamlines around the ball:
The closer the streamlines, the faster the flow. The flow is moving faster on the bottom of the ball since the streamlines are closer.
Now onto you specific question of why it bounces differently. Let's look at the forces on the ball in back-spin:
When the ball hits the ground on the other side of the court, the upward vertical velocity (speed moving up) that it leaves the ground with is proportional to the downward vertical velocity (speed moving down) that it hits the ground with. There are two forces in the up and down direction on the ball: the gravitational force and the lift force as seen in the picture above. In a back spin shot, the lift force is up. If we only look at the velocity of the ball in the vertical direction, you can see that the ball will fall slower to the ground since there is an additional force on the ball up. Thus, the ball will hit the opposite side of the court with less vertical velocity and thus not bounce as high as "usual". The reverse is true for a top-spin shot. The top-spin increases the downward force and increases the velocity in which it hits the ground since the aerodynamic and gravitational forces both force the ball down. This increases the bounce height. (Note that I have neglected the fact that the lift force direction is perpendicular to motion and not gravity. But since the ball moves perpendicular to gravity most of the time, this is a good assumption and way of showing the physics.)
There is also the friction effect when the ball hits the ground. This changes the trajectory of the ball and would have the opposite perceived effect on bounce height as above:
The change in ball direction does not affect the bounce height as much as the difference in vertical velocity when the ball hits the ground. Note that this balance of effects is greatly dependent on the velocity of the ball. Since the tennis pros hit the ball at a very fast speed, the pressure forces have a greater affect than the frictional forces when the ball hits the ground. When amateurs play tennis, they may spin the ball with the same rotational velocity but without the horizontal speed to cause much curving of the ball. This would cause a higher bounce with back-spin and lower with top-spin. As with everything, it is a balancing of forces.
It certainly does not have topspin at any point. The first reason is correct. It has less backspin and therefore appears to drop. The camera angle from behind the pitcher is deceiving. Although it appears to drop off suddenly, it is more gradual than it appears. A straight fastball defies gravity quite a bit, as does a split fingered fastball, because they both have backspin. The splitter just does not defy gravity nearly as much. The best splitters have relatively high velocity to mimic a fastball, but reduced backspin to get the “drop” action.
Best Answer
There is a mechanism between each set of 'leaf pairs'
that allows the pair above to rotate slightly further than the one underneath.
The image was from this youtube clip 'How to make a Helicone'.