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A SMALL IDEA. A LITTLE GRAVITY.

Gravity Sketch.

Air currents. Buoyant gel. Parachute silk.
Draw something that changes what happens next.

WELCOME TO YOUR SKETCHBOOK

A line can change everything.

  1. Draw a ramp under the coral ball with your finger or mouse. Use Line to drag a preview, or tap a start and move the pointer before placing the end.
  2. Drop the ball. Press Space or click Drop the ball. With Auto-drop on, the ball releases five seconds after you finish drawing; starting another stroke restarts the countdown. Turn Auto-drop off to plan for longer. Moving drawings still need Release drawing first. During a run, each part of a freehand stroke becomes solid immediately, before you release the mouse or lift your finger. Roll, fall and bounce into the green cup. Let the ball settle to finish.
  3. Earn stars. Complete a puzzle in one stroke for 3 stars, two strokes for 2, or three or more for 1. Undo and Erase do not refund a stroke. An unsuccessful attempt clears this puzzle’s lines and restores its ink and stroke count. Choose Try again to start with an empty board. Earned stars and completed puzzles stay saved. Clear asks before discarding a sketch while you are editing. In the lab, Reset ball keeps your experiment.

Material worlds & cart relays

Blue buoyant gel lifts the ball. Amber syrup slows it. Air currents push it sideways. Blue helium ribbons float upward; rose parachute silk drifts down slowly. Release moving drawings before dropping the ball. In cart relays, land the ball in the tray first. A latch secures the cargo. The loaded cart starts rolling and the striped gap opens for drawing. Sketch a fixed bridge while it moves. New contraptions mix falling orange strikers with green catching ramps, counterweight levers, crates, moving silk and ribbon elevators. Build tracks continuously: the ball or cart can use the part you have already drawn. Pause and half speed are available. If the delivery fails, its drawings clear for a fresh attempt.

Explore the physics

All 36 puzzles use Earth gravity and a 1 kg ball. In the lab, vary mass, gravity and bounce. Weight = mass × gravity. With no air resistance, light and heavy balls fall equally fast; their collisions differ. The lab block has a 2 kg mass, and its seesaw has a 1.5 kg mass.

The bounce coefficient sets rebound speed relative to impact speed. Friction slows sliding and creates rolling. Half speed slows playback, not gravity. Green ramps stay fixed. Purple spring surfaces stay fixed but rebound strongly. Orange falling ramps move, rotate and rebound. Choose a material before drawing. In timing puzzles, Drop drawing first; the ball stays held. Release it when your curve is in the right position. Pause and half speed help you study the motion. Red zones end a run; hatched zones cannot be drawn on. Challenges limit your ink and number of lines. Failed attempts clear the sketch automatically. Winning sketches remain available to refine with Edit & retry. Clear begins a fresh attempt with a fresh stroke count.

Keyboard & touch

Focus the board with Tab. Arrow keys move the pencil (Shift for small steps); Enter sets a line’s start and end. Escape cancels it. Space drops the ball when it is ready. All other controls work with Tab and Enter. On a phone, draw directly on the board; scroll from outside it. Focus hides the surrounding notes for more playing space. Portrait orientation gives the drawing board the most room.

Your challenge book

All 36 illustrated squares are visible from the start. Level 1 is open; complete every earlier level to unlock a higher one. Any successful finish counts—you do not need three stars. Locked previews remain visible. Choose an unlocked preview to play or replay. Use the filters to find beginner, harder, moving-ramp or expert puzzles. The physics lab is separate from the 36 levels. All levels returns to the book and pauses an active run; Continue sketch returns to it.

Your progress

Drawings, each puzzle’s best star rating, completed puzzles and lab settings save only in this browser. Completing an already-finished puzzle with fewer stars will not lower its best rating. Earlier completions remain marked with a check until you replay them to earn stars. Clearing browser data removes them. A dashed idea is only a guide—trace it or invent your own route. There is no timer penalty and no online leaderboard.

About this simulation

Uses the locally served Planck physics engine. Metres, kilograms and seconds; fixed 120 Hz simulation. This is a simplified 2D model: ideal rigid bodies, with stylized lift and drag in the material worlds. It is not a prediction of real materials. Provided as is, with no guarantee of accuracy or suitability; use at your own discretion.

Clear this drawing?

Your completed puzzles and best stars stay saved. Only this page’s lines and stroke count will be cleared.