Some things to get to entertain my grandsons in the future.

Wondering if it is possible to make a "bouncer".

1. Stiffen the copper wire* before turning it into a spring making it slightly longer than the battery plus magnets with the "top" end bent across the diameter to make contact with the battery's positive end. To stiffen the wire first clamp one end somehow (in a vice, under a screw head), winding the wire once round a screwdriver as near to the clamp as you can get then (wearing work gloves) pull a bit on the free end with pliers and then pull the screwdiver toward you so the wire has to "slide round it", do not let the screwdriver rotate. This work hardens and "stretches" the wire on one side encouraging it to coil. Do this twice for extra hardness/coiliness.

2. Assemble a 2p coin (copper allow coated steel) or plated steel "penny" washer, mangets and battery positive up. The coin/washer forms the negative contact for the coil.

3. Hot melt glue or Bluetack magnets to end of coil with bend, this acts as a coul compression load. However, if the coil magnets are in oposition to the bottom ones, N to N say, they may help the action by giving added "lift", but the coil may end up floating. If the magnets attract it may not bounce or the coil may need to be adjusted longer. The strength and weight of the coil magnets will also enter the equation.

4. Hold coil, its nagnets up, over battery and drop.

5. Adjust the coil to ensure that, as it compresses, the bent end touches the positive pimple.

*Suitable wire (in the UK anyway) can be got from mains house wiring cable. I'm going for 1.5mm diameter.

From the formula F=BIL the force on the coil will equal the product of the magnetic field strength, the length of wire in the field and the current through that wire. One of the few formulas I remember from my City and Guilds course in 1973! So, the more turns the merrier, but leave room for a bit of compression!