You move immediately, instead of accelerating, when you do inputs.
Video Game Physics, Acceptable Breaks from Reality.
In Video Game world, it often seems that the player is not exerting force onto the world, but are directly modifying the velocity of the thing s/he has control. There is no such thing as momentum. Or inertia. In lots of Platformers or other games where you controls a object, the character move, stop, turn, and jump exactly according to your input, without any delay in the actual speed. In (less realistic) driving games, the vehicle turns exactly according to the direction you pressed, while in reality you need time to steer the wheels or handle to make the turn, so actually you need to steer in advance. Of course, this is not bad. Before physics engine becomes commonplace, lots of games weren't able to actually carry out acceleration, so it become simplified as this trope. And even at now where you have lots of physic engines at hand, you may also want to simplify things by removing the acceleration, so that players can have better control. It's technically averted in a lot of games, though in a manner that most wouldn't notice. The rate of acceleration is high and the speed cap is low, so you're moving at the maximum speed very shortly after pushing the button. Super Trope of Instant 180 Degree Turn. Contrast Frictionless Ice, where you can only accelerate/decelerate on it, in a rather painful way. See also Jump Physics. Related to Space Friction. Only aversions should be listed - this is a very common Video Game trope. But for games like flight and driving simulators where proper demonstration of inertia is needed, since it's necessary to avert this trope, straight examples should be listed instead.