Jump Quest I — Scratch L3 Lesson 29

Learnt28 min · a speed that grows, and landing on the grass
Basic24 min · Pico on the meadow
Challenge 1–327 min · three gravities, the slow climb, a bouncing ball
Extrabonus · a shower of stars

WHAT IT SHOULD LOOK LIKE

The same drop, twice. Moving the same amount every tick looks like a lift. A speed that grows every tick looks like falling.

5 every tick

a speed that grows

faded sprite = where it ends up · panels run left to right

Review — the Cheese Maze arc 5 min

Walls are one flat colour, and a sprite asks whether it is touching it.
Move, ask, undo — the check comes after the move, never before.
A step bigger than the wall is thick steps straight over it.

Quick-fire

In the maze, the mouse moved 4 and undid exactly 4. When Pico falls onto the grass, how far does it need to go back up?

Reveal the answer

Nobody knows in advance — it depends how fast Pico was falling. So instead of undoing a number, Pico backs up one pixel at a time until it is clear of the grass. That is today’s landing.

Today’s Topic 3 min

y velocity — a speed kept in a variable
Gravity: change [y velocity v] by (-1) every tick
Landing: pushing back out of the ground
Why the landing lives in a My Block with screen refresh turned off

Learning outcome

By the end of this lesson you will be able to:

Make a sprite fall faster and faster, the way real things do.
Land it exactly on the ground — not in it, not above it.
Explain why the push-out has to finish between two frames.

Learnt — falling 28 min

1 · A steady fall looks wrong

Here is the first fall most people build: move down 5 every tick until you touch the grass.


repeat until <touching color [#3FA34D]?>
  change y by (-5)
end

It works. Watch it and decide whether it looks like falling.

WHAT IT SHOULD LOOK LIKE

Five pixels every tick, from the first tick to the last. It gets there, but nothing about it says “falling”.

49 ticks, all the same

faded sprite = where it ends up

Runs here in the page. Nothing to install.

How to use this: Click the green flag and watch Pico come down at one speed the whole way.

49 ticks, every one the same. It looks like a lift going down, not something dropping.

2 · A speed you can change

Things that fall start slowly and get faster. To copy that, the speed cannot be a number typed into a block — it has to live in a variable that changes every tick. We call it y velocity: how fast Pico is moving up right now.


set [y velocity v] to (0)
repeat until <touching color [#3FA34D]?>
  change [y velocity v] by (-1)
  change y by (y velocity)
end

Two blocks. The first is gravity: it takes one off the speed. The second spends the speed.

Tick	y velocity	Pico moves	Fallen so far
1	−1	1 down	1
2	−2	2 down	3
3	−3	3 down	6
10	−10	10 down	55
22	−22	22 down	253

Negative means down. y velocity is how fast Pico goes up. A speed of −22 is 22 pixels a tick downwards. Next lesson a jump will be a positive number, and the same two blocks will carry Pico up, slow it and bring it back.

WHAT IT SHOULD LOOK LIKE

One pixel, then two, then three… The gaps between the pictures grow, and the whole fall takes 22 ticks instead of 49.

the speed grows every tick

faded sprite = where it ends up

Runs here in the page. Nothing to install.

How to use this: Click the green flag. Watch the y velocity monitor count down while Pico speeds up.

22 ticks instead of 49, and a landing speed of −22. Slow at the top, fast at the bottom.

3 · Landing: back out of the grass

Look closely at the end of that fall. The last tick moved Pico 22 pixels, but the grass was nearer than that — so Pico finished 9 pixels inside it. The fix is the maze’s undo, with a twist: we do not know how far to go back, so we go back one pixel at a time until Pico is clear.


define land
if <touching color [#3FA34D]?> then
  repeat until <not <touching color [#3FA34D]?>>
    change y by (1)
  end
  set [y velocity v] to (0)
end

A My Block called land, made with Run without screen refresh ticked — Challenge 2 shows why that tick matters.

WHAT IT SHOULD LOOK LIKE

The last tick moves Pico 22 pixels, and the grass was only 13 away — so Pico ends up 9 pixels inside it. The push-out lifts it back, one pixel at a time.

the tick it lands

after the push-out

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag. Pico lands, stops for a moment inside the grass so you can see it, then pushes out.

Pushed up 9 pixels in one go. Now Pico is standing ON the grass.

Basic — Pico on the meadow 24 min

Start a new project. You are painting a meadow and dropping Pico into it — then walking it off a ledge to watch it fall again.

Step 1 — paint the meadow

Paint a pale sky backdrop.
With the rectangle tool, draw a strip of ground across the bottom in one green. Fill on, outline off.
Draw a short, thin ledge high up on the right in the same green.

Step 2 — Pico

Add the Pico sprite and set its size to 40.
Add set rotation style [left-right v] so turning round never turns it upside down.
Make a variable called y velocity.

Step 3 — the land block

In My Blocks, click Make a Block and call it land.
Tick Run without screen refresh before you press OK.
Under the define hat, build the push-out from Learnt part 3.

Step 4 — the loop

When the flag is clicked, go to x: 150, y: 150 — above the ledge — and set y velocity to 0.
In a forever: gravity, then change y by (y velocity), then land :: custom.
Test it. Pico should drop onto the ledge and stay there.

Step 5 — walking, and falling off

Inside the loop, add the right and left arrow checks: point the right way and change x by (4) or change x by (-4).
Walk Pico off the end of the ledge. It should fall to the ground, speeding up.
Add when [space v] key pressed → go to x: (x position) y: (150) and set y velocity to 0, so you can drop it again.


when flag clicked
set rotation style [left-right v]
go to x: (150) y: (150)
set [y velocity v] to (0)
forever
  change [y velocity v] by (-1)
  change y by (y velocity)
  land :: custom
  if <key (right arrow v) pressed?> then
    point in direction (90)
    change x by (4)
  end
  if <key (left arrow v) pressed?> then
    point in direction (-90)
    change x by (-4)
  end
end

when [space v] key pressed
go to x: (x position) y: (150)
set [y velocity v] to (0)

The whole of Pico, with the land block from Step 3.

Runs here in the page. Nothing to install.

How to use this: Click the green flag. Walk with the left and right arrows, walk off the ledge, and press space to drop Pico from the sky again.

What you are aiming at. Pico falls, lands on whatever is green, and falls again when it walks off.

Pico sinks into the ground and then climbs slowly out.

Run without screen refresh is not ticked. Right-click the define hat, choose Edit, and tick it. Challenge 2 is all about this.

Pico falls straight through the ground.

The colour in touching color is not the ground’s. Click the swatch and pick the ground with the eyedropper from the Stage.

Pico shoots up out of the top of the Stage the moment it lands.

The push-out says change y by (-1), or the not is missing — so it keeps going while it is not touching.

Pico keeps sinking a little further each time.

y velocity is never set back to 0 inside land, so every tick starts from the speed it landed at.

If I stop right on the edge of the ledge, Pico hangs there by its head.

Well spotted — Pico’s head is much wider than its feet, and the head is still over the ledge. Keep walking and it drops. Lesson 3-31 fixes it properly.

CHALLENGE 1 · L3-29-M1🪙 30 Adcoins8 min

Three gravities

Drop three Picos together from the same height — one on the Moon, one on Earth, one on a giant planet.

Their gravities are 0.5, 1 and 2.
Each one counts its ticks until it lands.
Before you run it, guess the three numbers.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — three Picos dropped together. Half the gravity takes 31 ticks, not 44; double the gravity takes 16, not 11.

all three landed

Runs here in the page. Nothing to install.

How to use this: Click the green flag. All three drop at once — watch which lands first, then read the monitors.

31, 22 and 16 ticks. Half the gravity is not twice as slow.

Done when: your three counts are on screen, and you can say what surprised you about them.

Teacher note

Nearly everyone guesses 44 and 11 — double and half of 22. The real answers are 31 and 16, because the distance fallen grows with the square of the time: 22 × 1.41 ≈ 31 and 22 ÷ 1.41 ≈ 16. Nobody needs the maths, but the gap between the guess and the result is the lesson: speed that builds up behaves differently from speed that is fixed.

CHALLENGE 2 · L3-29-M2🪙 50 Adcoins9 min

The slow climb

Make two Picos. Give both the same land block, but tick Run without screen refresh on only one of them.

Drop both from the same height.
A second script on each counts every frame it sees Pico touching the grass.
Compare the two counters.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — the same landing twice. Ticked, Pico is never drawn inside the grass. Not ticked, you watch it climb out: 11 frames.

a moment after landing

Runs here in the page. Nothing to install.

How to use this: Click the green flag and watch the right-hand Pico closely as it lands.

0 frames against 11. Both push out the same number of pixels — only one lets you watch.

Done when: both counters are on screen and you can say, in one sentence, what the tickbox changes.

Teacher reveal — the counting script


when flag clicked
wait (1) seconds
forever
  if <touching color [#3FA34D]?> then
    change [frames in the grass v] by (1)
  end
end

Both Picos climb out the same number of pixels. The difference is when the Stage is drawn. Without the tick, Scratch redraws after every pass of the repeat until, so each pixel of the climb is a frame you can see. With it, the whole climb happens between two frames and the watcher never catches Pico in the grass. This is the Firework Show tickbox from Lesson 3-15, doing a job that actually matters.

CHALLENGE 3 · L3-29-M3🪙 70 Adcoins10 min

A bouncing ball

Swap Pico for a ball. When it lands, instead of stopping, it should bounce — a little lower every time — and then settle.

Landing turns the speed round and keeps seven tenths of it.
A counter of bounces.
When a bounce would be tiny, the ball stops for good.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — every landing turns the speed round and keeps seven tenths of it. Each bounce is lower, and after seven the ball stays down.

seven bounces, then rest

faded sprite = where it ends up

Runs here in the page. Nothing to install.

How to use this: Click the green flag and count the bounces with the monitor.

Seven bounces, each lower than the last, and then the ball stays on the grass.

Done when: the ball bounces at least four times, each lower than the one before, and then rests on the grass without twitching.

Teacher reveal — the bounce block


define bounce
if <touching color [#3FA34D]?> then
  repeat until <not <touching color [#3FA34D]?>>
    change y by (1)
  end
  set [y velocity v] to (round ((y velocity) * (-0.7)))
  change [bounces v] by (1)
  if <(y velocity) < (3)> then
    set [y velocity v] to (0)
    set [resting v] to (1)
  end
end

Two details that trip people up. The round is there because 0.7 of a whole number is rarely whole, and without it the speed never settles. The resting test is there because a bounce of 1 bounces for ever — the ball twitches on the grass until you stop the project.

EXTRA MISSION · L3-29-MX🪙 100 Adcoinsbonus

A shower of stars

Ten stars drop from random heights at random places. Every one falls the way Pico does, and lands on whatever green is below it.

One Star sprite, ten clones.
Each clone keeps its own y velocity — made for this sprite only, as in Bubble Popper.
All of them share one land block.
A landed counter, and Pico announcing when it reaches 10.

WHAT IT SHOULD LOOK LIKE

Extra — ten clones, ten speeds, one landing block. The stars that drop over the ledge land on it: it is the same green.

all ten down

Runs here in the page. Nothing to install.

How to use this: Click the green flag and watch ten stars drop. Pico speaks when the last one lands.

Ten speeds, one landing block — and the stars over the ledge land on the ledge.

Teacher note

The stars that land on the ledge are the best moment in the lesson: nobody wrote anything about the ledge. It is green, so it is ground. Next lesson the same idea turns into platforms you can jump onto.

Summary 5 min

A fall that looks real needs a speed that changes, so the speed lives in a variable: y velocity.
Gravity is change [y velocity v] by (-1); moving is change y by (y velocity).
Landing overshoots, so push back out one pixel at a time until clear.
Then set y velocity to 0, or the next tick punches straight back in.
The push-out goes in a My Block with Run without screen refresh ticked, so it finishes between two frames.

Velocity: How fast something is moving, and which way. Negative y velocity is downwards.
Gravity: The steady pull that takes a little off the velocity every tick.
Tick: One pass round the forever loop — one frame of the game.
Push-out: Moving a sprite back out of the ground after it has gone too far in.

Hand in

Save your meadow. Next lesson Pico jumps — and a jump turns out to be a single block.

Learnt28 min · a speed that grows, and landing on the grass
Basic24 min · Pico on the meadow
Challenge 1–327 min · three gravities, the slow climb, a bouncing ball
Extrabonus · a shower of stars

WHAT IT SHOULD LOOK LIKE

The same drop, twice. Moving the same amount every tick looks like a lift. A speed that grows every tick looks like falling.

5 every tick

a speed that grows

faded sprite = where it ends up · panels run left to right

Review — the Cheese Maze arc 5 min

Walls are one flat colour, and a sprite asks whether it is touching it.
Move, ask, undo — the check comes after the move, never before.
A step bigger than the wall is thick steps straight over it.

Quick-fire

In the maze, the mouse moved 4 and undid exactly 4. When Pico falls onto the grass, how far does it need to go back up?

Reveal the answer

Nobody knows in advance — it depends how fast Pico was falling. So instead of undoing a number, Pico backs up one pixel at a time until it is clear of the grass. That is today’s landing.

Today’s Topic 3 min

y velocity — a speed kept in a variable
Gravity: change [y velocity v] by (-1) every tick
Landing: pushing back out of the ground
Why the landing lives in a My Block with screen refresh turned off

Learning outcome

By the end of this lesson you will be able to:

Make a sprite fall faster and faster, the way real things do.
Land it exactly on the ground — not in it, not above it.
Explain why the push-out has to finish between two frames.

Learnt — falling 28 min

1 · A steady fall looks wrong

Here is the first fall most people build: move down 5 every tick until you touch the grass.


repeat until <touching color [#3FA34D]?>
  change y by (-5)
end

It works. Watch it and decide whether it looks like falling.

WHAT IT SHOULD LOOK LIKE

Five pixels every tick, from the first tick to the last. It gets there, but nothing about it says “falling”.

49 ticks, all the same

faded sprite = where it ends up

Runs here in the page. Nothing to install.

How to use this: Click the green flag and watch Pico come down at one speed the whole way.

49 ticks, every one the same. It looks like a lift going down, not something dropping.

2 · A speed you can change


set [y velocity v] to (0)
repeat until <touching color [#3FA34D]?>
  change [y velocity v] by (-1)
  change y by (y velocity)
end

Two blocks. The first is gravity: it takes one off the speed. The second spends the speed.

Tick	y velocity	Pico moves	Fallen so far
1	−1	1 down	1
2	−2	2 down	3
3	−3	3 down	6
10	−10	10 down	55
22	−22	22 down	253

WHAT IT SHOULD LOOK LIKE

One pixel, then two, then three… The gaps between the pictures grow, and the whole fall takes 22 ticks instead of 49.

the speed grows every tick

faded sprite = where it ends up

Runs here in the page. Nothing to install.

How to use this: Click the green flag. Watch the y velocity monitor count down while Pico speeds up.

22 ticks instead of 49, and a landing speed of −22. Slow at the top, fast at the bottom.

3 · Landing: back out of the grass


define land
if <touching color [#3FA34D]?> then
  repeat until <not <touching color [#3FA34D]?>>
    change y by (1)
  end
  set [y velocity v] to (0)
end

A My Block called land, made with Run without screen refresh ticked — Challenge 2 shows why that tick matters.

WHAT IT SHOULD LOOK LIKE

The last tick moves Pico 22 pixels, and the grass was only 13 away — so Pico ends up 9 pixels inside it. The push-out lifts it back, one pixel at a time.

the tick it lands

after the push-out

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag. Pico lands, stops for a moment inside the grass so you can see it, then pushes out.

Pushed up 9 pixels in one go. Now Pico is standing ON the grass.

Basic — Pico on the meadow 24 min

Start a new project. You are painting a meadow and dropping Pico into it — then walking it off a ledge to watch it fall again.

Step 1 — paint the meadow

Paint a pale sky backdrop.
With the rectangle tool, draw a strip of ground across the bottom in one green. Fill on, outline off.
Draw a short, thin ledge high up on the right in the same green.

Step 2 — Pico

Add the Pico sprite and set its size to 40.
Add set rotation style [left-right v] so turning round never turns it upside down.
Make a variable called y velocity.

Step 3 — the land block

In My Blocks, click Make a Block and call it land.
Tick Run without screen refresh before you press OK.
Under the define hat, build the push-out from Learnt part 3.

Step 4 — the loop

When the flag is clicked, go to x: 150, y: 150 — above the ledge — and set y velocity to 0.
In a forever: gravity, then change y by (y velocity), then land :: custom.
Test it. Pico should drop onto the ledge and stay there.

Step 5 — walking, and falling off

Inside the loop, add the right and left arrow checks: point the right way and change x by (4) or change x by (-4).
Walk Pico off the end of the ledge. It should fall to the ground, speeding up.
Add when [space v] key pressed → go to x: (x position) y: (150) and set y velocity to 0, so you can drop it again.


when flag clicked
set rotation style [left-right v]
go to x: (150) y: (150)
set [y velocity v] to (0)
forever
  change [y velocity v] by (-1)
  change y by (y velocity)
  land :: custom
  if <key (right arrow v) pressed?> then
    point in direction (90)
    change x by (4)
  end
  if <key (left arrow v) pressed?> then
    point in direction (-90)
    change x by (-4)
  end
end

when [space v] key pressed
go to x: (x position) y: (150)
set [y velocity v] to (0)

The whole of Pico, with the land block from Step 3.

Runs here in the page. Nothing to install.

How to use this: Click the green flag. Walk with the left and right arrows, walk off the ledge, and press space to drop Pico from the sky again.

What you are aiming at. Pico falls, lands on whatever is green, and falls again when it walks off.

Pico sinks into the ground and then climbs slowly out.

Run without screen refresh is not ticked. Right-click the define hat, choose Edit, and tick it. Challenge 2 is all about this.

Pico falls straight through the ground.

The colour in touching color is not the ground’s. Click the swatch and pick the ground with the eyedropper from the Stage.

Pico shoots up out of the top of the Stage the moment it lands.

The push-out says change y by (-1), or the not is missing — so it keeps going while it is not touching.

Pico keeps sinking a little further each time.

y velocity is never set back to 0 inside land, so every tick starts from the speed it landed at.

If I stop right on the edge of the ledge, Pico hangs there by its head.

Well spotted — Pico’s head is much wider than its feet, and the head is still over the ledge. Keep walking and it drops. Lesson 3-31 fixes it properly.

CHALLENGE 1 · L3-29-M1🪙 30 Adcoins8 min

Three gravities

Drop three Picos together from the same height — one on the Moon, one on Earth, one on a giant planet.

Their gravities are 0.5, 1 and 2.
Each one counts its ticks until it lands.
Before you run it, guess the three numbers.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — three Picos dropped together. Half the gravity takes 31 ticks, not 44; double the gravity takes 16, not 11.

all three landed

Runs here in the page. Nothing to install.

How to use this: Click the green flag. All three drop at once — watch which lands first, then read the monitors.

31, 22 and 16 ticks. Half the gravity is not twice as slow.

Done when: your three counts are on screen, and you can say what surprised you about them.

Teacher note

CHALLENGE 2 · L3-29-M2🪙 50 Adcoins9 min

The slow climb

Make two Picos. Give both the same land block, but tick Run without screen refresh on only one of them.

Drop both from the same height.
A second script on each counts every frame it sees Pico touching the grass.
Compare the two counters.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — the same landing twice. Ticked, Pico is never drawn inside the grass. Not ticked, you watch it climb out: 11 frames.

a moment after landing

Runs here in the page. Nothing to install.

How to use this: Click the green flag and watch the right-hand Pico closely as it lands.

0 frames against 11. Both push out the same number of pixels — only one lets you watch.

Done when: both counters are on screen and you can say, in one sentence, what the tickbox changes.

Teacher reveal — the counting script


when flag clicked
wait (1) seconds
forever
  if <touching color [#3FA34D]?> then
    change [frames in the grass v] by (1)
  end
end

CHALLENGE 3 · L3-29-M3🪙 70 Adcoins10 min

A bouncing ball

Swap Pico for a ball. When it lands, instead of stopping, it should bounce — a little lower every time — and then settle.

Landing turns the speed round and keeps seven tenths of it.
A counter of bounces.
When a bounce would be tiny, the ball stops for good.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — every landing turns the speed round and keeps seven tenths of it. Each bounce is lower, and after seven the ball stays down.

seven bounces, then rest

faded sprite = where it ends up

Runs here in the page. Nothing to install.

How to use this: Click the green flag and count the bounces with the monitor.

Seven bounces, each lower than the last, and then the ball stays on the grass.

Done when: the ball bounces at least four times, each lower than the one before, and then rests on the grass without twitching.

Teacher reveal — the bounce block


define bounce
if <touching color [#3FA34D]?> then
  repeat until <not <touching color [#3FA34D]?>>
    change y by (1)
  end
  set [y velocity v] to (round ((y velocity) * (-0.7)))
  change [bounces v] by (1)
  if <(y velocity) < (3)> then
    set [y velocity v] to (0)
    set [resting v] to (1)
  end
end

EXTRA MISSION · L3-29-MX🪙 100 Adcoinsbonus

A shower of stars

Ten stars drop from random heights at random places. Every one falls the way Pico does, and lands on whatever green is below it.

One Star sprite, ten clones.
Each clone keeps its own y velocity — made for this sprite only, as in Bubble Popper.
All of them share one land block.
A landed counter, and Pico announcing when it reaches 10.

WHAT IT SHOULD LOOK LIKE

Extra — ten clones, ten speeds, one landing block. The stars that drop over the ledge land on it: it is the same green.

all ten down

Runs here in the page. Nothing to install.

How to use this: Click the green flag and watch ten stars drop. Pico speaks when the last one lands.

Ten speeds, one landing block — and the stars over the ledge land on the ledge.

Teacher note

Summary 5 min

A fall that looks real needs a speed that changes, so the speed lives in a variable: y velocity.
Gravity is change [y velocity v] by (-1); moving is change y by (y velocity).
Landing overshoots, so push back out one pixel at a time until clear.
Then set y velocity to 0, or the next tick punches straight back in.
The push-out goes in a My Block with Run without screen refresh ticked, so it finishes between two frames.

Velocity: How fast something is moving, and which way. Negative y velocity is downwards.
Gravity: The steady pull that takes a little off the velocity every tick.
Tick: One pass round the forever loop — one frame of the game.
Push-out: Moving a sprite back out of the ground after it has gone too far in.

Hand in

Save your meadow. Next lesson Pico jumps — and a jump turns out to be a single block.