We tend to think of breaking the sound barrier as a comparatively modern accomplishment, but on a smaller scale, cattle herders have been breaking it for centuries: the cracking sound of the tip of a bullwhip snapping comes from a small-scale sonic boom. Reliably getting a crack out of a whip takes skill and practice, though, which is why [Craig Turner] built a whip-cracking machine.

The first step was to build the whip itself, which was surprisingly complicated. Bullwhips taper down toward the end of the whip. As the whip uncurls during a crack, momentum passes down the whip; since the whip becomes continually narrower and lighter, conservation of momentum means that different stretches of the whip must move progressively faster. To get this effect, [Craig] joined together a series of increasingly thin and light ropes. The heavy end of the whip terminated in an eyelet connected to a length of elastic shock cord. Stretching the whip back on the shock cord and releasing it whipped it around, resulting in a fairly reliable crack.

For greater convenience, [Craig] built this into a launcher mechanism, with the elastic cord wrapped around the end of the launcher, an electrical-conduit guide for the whip, and a spring-loaded trigger mechanism to release it. This worked even better than expected, getting a reliable crack every time. The tip of the whip could slice leaves, tear open aluminium cans, put out candle flames, knock the cap off a bottle without tipping it over, and reliably hit small targets on the first shot.

As [Craig] mentioned, this setup would make it much easier to study the cracking effect with a schlieren imaging setup.

The Claymore mine is a rather fearsome weapon of war, using explosives to blast a cone of shrapnel towards advancing enemies. It’s not really something you should try and build at home. An airsoft version, though, is altogether more appropriate. [RegiBlackwood] has developed a simple way to build exactly that.

It’s a cheap and cheerful build, with the claymore housing itself built out of cardboard. Wooden dowels are used to stake it into the ground, just like the real thing. In the center of the housing sits a regular old mouse trap. Only, it’s been modified to hold a sling carrying a payload of BBs. The trap is also tweaked to make its spring more powerful, and to enable it to be triggered with the tug of a tripwire. When triggered, the mousetrap fires and hurls the sling forth, spewing a rain of BBs from the front of the device—ideally quelling the advance on your position.

Built properly, it’s a fun piece of airsoft hardware that could really change the dynamics of your regular game. If you’re looking to do point defence, you might also consider building yourself some automated turrets as well…