A smaller ball, different walls

Challenge 6 of 16

Change the ball and both walls have to move with it. This one is 56 across, so it clears each edge by 28 rather than 40, which puts its walls at 28 and 372 — every wall depends on the ball's size.

Set them both.

Your code JavaScript

Set them both.

Console print() output

0 / 50 frames · 400×400

Target

Yours

Yours over Target — ghosted shapes are in the target but missing from yours

Results

Press Run to check your code

Penalties: none this run

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Lesson Bouncing

The whole trick is a minus sign.

speed = -speed; takes whatever the speed is and makes it the opposite: 12 becomes -12, and -12 becomes 12. Nothing moves the ball backwards. The ball keeps doing exactly what it always did, adding its speed, and the speed is what changed.

What if does.

if (x > 360) { speed = -speed; } means: only do the thing in the curly brackets when the test in the round brackets is true. Every if in this topic is written for you, with a comment above it saying what it is watching for, so you never have to write one yourself. You choose the numbers.

One wall is never enough.

A ball that only checks the right-hand side turns around once and then leaves on the left, forever. Each edge you want it to come back from needs its own if — which is why the later challenges have four of them, one per side.

Use the arrows.

The turn happens in a single frame, and at normal speed you cannot see it. Step one frame at a time with the arrows either side of the playbar and watch the readout: the position stops climbing and starts falling, and nothing else on the line changed.