The world is deceptive. Idealizations Make physics simple
Sometimes the universe just too complex for analysis.
Heck, if you take a tennis ball and throw it around the room, that's even too complicated. After leaving your hand, the ball has a gravitational interaction with the Earth, which causes it to accelerate towards the ground. The ball spins as it moves, which means that there may be more drag on one side of the ball than on the other. The ball also hits some of the oxygen and nitrogen molecules in the air - and some these molecules interact with even more air. The air itself is not even stable - the density changes as the ball moves higher, and the air can move. (We usually say that wind.) And once the ball hits the ground, even the floor is not very smooth. Yes, it looks smooth, but it's on the surface of a spherical planet.
But all is not lost. We can still model this tossed tennis ball. All we need are some relevant things. These simplify estimates that turn an impossible problem into a solvable problem.
In the case of the tennis ball, we can assume that the whole mass is round at one point (in other words, the ball does not have real dimensions) and that the only force acting on it is the force. stable gravity that slows down. Why is it okay to overlook these other links? This is because they do not just make a big difference (or even measure).
Is this even legal in a physics court? Well, science is about the process of building models, including an equation for the path of a tennis ball. At the end of the day, if the experimental observations (where the ball lands) agree with the model (the prediction of where it will land), we'm good to go. For the tennis ball celebration, everything works very well. Of course, tossed ball physics is going to be a test question in a beginner physics class. Other ideologies are more difficult, such as trying to determine the curvature of the Earth just by looking at this long platform at Atlanta airport. But physicists do this kind of thing all the time.
Galileo Galilei made perhaps the most famous mark when he studied the nature of the movement. He was trying to figure out what would happen to a moving object if you don't force it. At the time, just everyone followed Aristotle's teaching, which said that if you do not force a moving object, it will stop and remain at rest. (Even though his work was around 1,800 years old, people thought Aristotle was too cool to be wrong.)
But Galileo disagreed. He thought he would keep moving at a steady pace.
If you want to study an object in motion, you need to measure both position and time so that you can measure its speed, or the change in position divided by the change in time. But there is a problem. How do you accurately measure the time for objects moving at high speeds over short distances? If you drop something even from a relatively small height, such as 10 meters, it will take less than 2 seconds for it to reach the ground. And back around the year 1600, when Galileo was alive, that was a very difficult time to measure. So instead, Galileo immediately watched him go down a path.