Levers, triggers and stored energy – harmless tabletop experiments

With a lever, it matters not only how hard you push but also where. Physicists call the product of force and distance from the pivot “torque”. If the torque on the left and right is equal, the ruler stays level. That is why a single coin balances two coins when it sits about twice as far from the pencil. This law of the lever is one of the oldest known laws of mechanics.

Stored energy is called “potential energy” in physics. When you carry the car up the ramp, you put work into it. That work is not lost but “parked” in the raised car. When you pull the gate card away, the potential energy turns into energy of motion. The higher the ramp, the more energy was stored and the further the car rolls – as long as it does not tip over.

A trigger works because a system is in a sensitive balance. An upright domino does stand, but even a slight tilt makes it fall. As it falls, it gives off energy that knocks over the next stone, and so on. The flick of your finger only supplies the tiny beginning; the real energy comes from all the stones you set up beforehand.

For the lever experiment you need identical coins, all of the same value. Different coins weigh different amounts, and then the calculation no longer works. Lay the coins flat and exactly on the centimetre marks so you can read the distances. A round pencil rolls away easily – a piece of tape under the pencil holds it in place.

For the ramp, a shallow angle is better than a steep one. If the ramp is too steep, the car tips forward or bounces onto the table at the end. Repeat each run several times and take the middle value, because small differences in how you let go change the result. That way you also learn how real researchers handle measurements.

With the dominoes, spacing decides everything. If they stand too far apart, a falling stone does not reach the next one. If they stand too close, they have too little swing. Try different spacings and watch when the chain runs reliably.

Levers are hidden in many things you use every day: a door handle is a lever that moves a latch with little force. Scissors are two levers with a shared pivot. A bottle opener, a wheelbarrow and even your forearm work on the same principle.

Stored energy and triggers are everywhere too. A click pen has a small spring that stores energy until a catch releases it. A light switch flips with a click because a spring pushes it over a tipping point. A wind-up alarm clock or a music box also uses a tensioned spring.

Precisely because stored energy can be released suddenly, machines have safety devices: covers, locks and switches that prevent unintended release. That is a good starting point for a conversation – why does a saw have a guard, and why must you not remove it?

The experiments themselves are harmless. The only real risk for small children is coins and small parts that can be swallowed. So put everything away after the experiment and do not let small children play with the materials unsupervised.

The most important rule is a boundary: these models stay tabletop experiments. None of it is turned into a device that encloses, holds, strikes or drops onto something, and none of it is used outdoors or with animals. Such devices cause animal suffering, often catch the wrong animals, can injure people and are banned in many countries.

That is why this knowledge base describes traps only as history, law and animal welfare – not as building instructions. When children ask how a trap works, the honest answer is: with exactly these basic principles, and that is precisely why it is dangerous and strictly regulated.

Turn the three experiments into a small research series. With the lever, you can put three, four or five coins on one side and predict each time where the single coin has to sit. Guess first, then check: that turns a game into a real experiment.

For the ramp, make a table: ramp height in one column, rolling distance in the other. After a few runs you will see that a higher ramp leads to a longer roll, but not without limit – friction and tipping set boundaries. Older children can think about where the energy goes in the end: into heat and sound.

Finally, discuss together where you find the principles around the house. Collect examples on a sheet of paper: levers, springs, triggers, safety catches. Then take everything apart and put it away – that is part of the experiment.