Well usually they don’t, and sometimes that’s intentional. But physics is just math and it comes down to looking at the formulas from the perspective of the game engine. Gravity is just downward force, and a collision detection to stop you going through the floor. Air resistance/friction; that’s negative force. And in fact, you can exploit that in some games.
A common misconception, however, is when something is labeled as a physics sim when it isn’t. Take water for example; real water simulations are massive particle simulations, even modern game engines can’t handle. How oceans are usually simulated, is with displacement, where they deform the mesh using rules that make it act like an ocean.
What it really comes down to, again, is taking the concept of what you want to do, and translating that to how you would program it. Another example is lighting. In real life, waves emit from the sun and bounce into our eyes, but that means a lot of those rays are unnecessary because you’ll never see them. So games do it in reverse, shooting the ray from the camera and checking if it hits a light source.
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