Workshop › Asteroids › Step 9 of 41

A little friction

What we are doing

Real space has no friction, but a game is nicer with a little: every frame both velocity parts are multiplied by 0.99, so a ship left alone slowly drifts to a stop.

```js
const FRICTION = 0.99

  ship.vx *= FRICTION
  ship.vy *= FRICTION
```

What it means

• *= multiplies: each frame the velocity keeps 99% of itself. After 60 frames about 55% is left.

Your turn

1. Under THRUST write FRICTION.
2. In update, above ship.x += ship.vx, write the two friction lines.

Skills: Velocity and gravity

← Thrust and drift A speed limit →

All steps

1. Black space
2. Where the ship is
3. Which way it points
4. A triangle ship
5. Which keys are down?
6. Turning
7. The game loop
8. Thrust and drift
9. A little friction
10. A speed limit
11. Around the screen
12. Making a bullet
13. Fire!
14. Bullets fly
15. A lifetime for bullets
16. Making a rock
17. Four big rocks
18. Drawing the rocks
19. Jagged rocks
20. Drifting rocks
21. When do two circles touch?
22. Breaking a rock
23. Bullets hit rocks
24. Points
25. Show the score
26. Losing a life
27. A rock hits the ship
28. Show the lives
29. What time is it?
30. A moment of safety
31. Blink while safe
32. Waves of rocks
33. The next wave
34. Faster every wave
35. One function to start
36. Playing or over
37. Game over
38. Best score
39. GAME OVER
40. Play again
41. Build it yourself: hyperspace