Lever and seesaw simulator

What this simulator shows

A seesaw is a lever: a stiff plank that turns around a pivot called the fulcrum. Pick a block weight from 1 to 4, then tap a spot on the plank to add it, or switch to Remove to take blocks off. The numbers under the plank show each spot's distance from the fulcrum, and the fulcrum itself can move three spaces either way. The readout adds up the turning effect on each side.

• Turning effect (called a moment) = weight × distance from the fulcrum.
• The seesaw balances when the total turning effect on the left equals the total on the right.
• A small weight far from the fulcrum can balance a big weight close to it: 1 × 6 balances 3 × 2.
• If the sides are not equal, the plank tips all the way toward the bigger side. The plank itself is treated as weightless.

Why hands-on helps

Most children have felt this on a real seesaw: a lighter child can balance a heavier one by sitting farther out. Placing and moving blocks lets them test that feeling and then find the rule for themselves. Because the numbers are whole, the rule becomes a times-table puzzle, and many children spot it before being told.

Common misconceptions

The usual first guess is that the weights must be equal to balance, or that the heavier side always goes down. Distance matters just as much as weight. Another mix-up is adding weights and distances instead of multiplying them. A third is thinking a block on the fulcrum pushes the plank down on one side; it has zero distance, so its turning effect is zero. Real seesaws and levers have their own weight, which this model leaves out to keep the rule clear.

A 10-minute lever activity

• Put a 2-block 3 spaces left. Ask the child to balance it with a 2-block, then with a 1-block, then with a 3-block.
• Record each balance as weight × distance on both sides. Ask what pattern they see.
• Clear the plank. Place a 3-block at the far left and a 1-block at the far right.
• Ask: "Without moving the blocks, how can you balance it?" (move the fulcrum toward the 3-block).
• Talk about where else this happens: a crowbar, a bottle opener, scissors.

Where this fits in school

• US, grades 3 to 8: levers and other simple machines appear in many elementary and middle school science and engineering units, and the balancing rule is good multiplication practice.
• England, Year 5: pupils recognize that some mechanisms, including levers, pulleys and gears, allow a smaller force to have a greater effect.
• England, Key Stage 3: pupils learn about the moment as the turning effect of a force, and later use the principle of moments to calculate balance.

A seesaw is a first-class lever: the fulcrum is between the effort and the load. Wheelbarrows and tweezers are other classes of lever, with the fulcrum in a different place.

Learning more

Forces and simple machines are part of Eurekami's science skill map, and the multiplication behind this tool is practiced in daily math sessions. When a question is tricky, the AI tutor asks guiding questions instead of giving the answer.