Game feel

Acceleration and friction in game development

speed builds up and bleeds off

Interactive example · scroll or point here to play

speed builds up and bleeds off

Acceleration and friction move the velocity toward the input speed by a set amount per second, instead of setting it in one frame. The bottom character reaches full speed in 0.2 s, stops 0.1 s after release, and brakes twice as hard when the input flips direction. The top character copies the input directly, so its speed trace is a square wave and it starts, stops and turns around in a single frame.

prompt bit

Give horizontal movement acceleration and friction: each frame move the velocity toward input times max speed with an acceleration that reaches max speed in 0.1 to 0.2 s, decelerate to a stop in about 0.1 s when no direction is held, use twice that deceleration when the input points against the current velocity, and halve both rates while airborne.

When to use it

Use acceleration to make movement build speed and deceleration to control how quickly the player stops. Different ground, air, and reversal rates can create distinct movement feel.

Implementation example

Engine-neutral pseudocode. Adapt the functions and coordinate conventions to your engine.

target = inputAxis * maxSpeed
rate = acceleration if inputAxis != 0 else deceleration
if target * velocity.x < 0: rate = reversalRate
velocity.x = moveTowards(velocity.x, target, rate * dt)

Common mistakes

A controller’s deceleration setting is not necessarily physical friction. Use consistent units and test reversals, airborne steering, and slopes at several frame rates.

Maintained by Nicolas Zullo · Follow on X ↗

When to use it

Implementation example

Common mistakes

Related concepts