Workshop › Pinball › Step 18 of 42

A bumper kicks

What we are doing

A wall gives back part of the speed; a bumper adds energy. We cancel the ball's speed into the bumper and give it a fixed kick of 6 outwards, so even a slow ball flies away.

```js
// A bumper kicks the ball away, faster than it came.
const vn = ball.vx * nx + ball.vy * ny
ball.vx += (-vn + 6) * nx
ball.vy += (-vn + 6) * ny
```

What it means

• vn is the speed along the normal (negative: towards the bumper).
• Adding -vn along the normal cancels it; adding 6 more sends the ball away at exactly 6, whatever it came in at.
• The speed along the bumper's edge is kept, so the ball glances off at an angle.

Your turn

In hitBumper, at the end, under ball.y = b.y + ..., write the comment and the three lines.

Skills: Velocity and gravity

← The ball meets a bumper A score and a fresh start →

All steps

1. Paint the table
2. Draw one wall
3. A list of walls
4. The game loop
5. A ball in the lane
6. Draw the ball
7. Move by the velocity
8. Launch with Space
9. Gravity
10. Does the ball touch a wall?
11. Push the ball out
12. Bounce off the wall
13. Small steps and a speed limit
14. Ready or playing
15. The next ball
16. Three bumpers
17. The ball meets a bumper
18. A bumper kicks
19. A score and a fresh start
20. Points for every hit
21. Remember which bumper was hit
22. Light it up
23. Lit for a moment, points once
24. Two flippers
25. Where is the tip?
26. Flippers stop the ball
27. Which keys are held?
28. Which way to turn
29. Flip!
30. A moving wall
31. The flipper throws
32. Three balls
33. Balls left and game over
34. Play again
35. Remember the best score
36. Launch on letting go
37. Pull the spring
38. Show the spring
39. Two thumbs
40. Pull with a finger
41. Tap to play again
42. Build it yourself: slingshots