We will not forget the wonderful shots of the darts in the movie: the heroes in the story waved their arms and threw a back darts back. The darts screamed in the air and made a beautiful curve to fly to the bad guys. Knocked down, then turned back to the owner’s hand. So, what is it that returns the darts back to the owner?
A Dutch physicist Felix Hess has been thinking about this since he was a child. When he was studying, he learned a lot of math and physics in school and wrote a 600-page book explaining why the darts can return to the master.
Hess wrote in the book: There are two main reasons why the darts can be rotated back. One is to return the special shape of the two arms of the dart, and the other is to throw it.
Let’s take a look at the “wings” of the shape of the dartnut banana: for each “wing”, it is the same as the wing of the plane – flat and convex. This shape enables the bounce back to be lifted by the airflow during flight. But the two wings are not the same, one with a “wing” surface facing the wind and the other away from the wind. This is like a wing of an airplane that extends backwards and then puts the aircraft into normal position. This type of aircraft is difficult to fly straight out, so the same is true for back darts.
The throwing method is also a factor in whether or not the dart can be rotated back. First of all, the darts in your hand should be kept upright, not horizontally like a flying saucer, with the plane facing forward. Then, with the power of the wrist, the darts are smashed into the air. The back darts will rotate continuously during the flight, just like flipping the head, about 10 laps per second, and the flight speed is about 100 km/h.
The back darts thrown by the right hand will be left to the left in the air. Hess used the example of cycling to explain this phenomenon. If you let go of the handlebar, as long as the body is tilted slightly to the left, the front wheel of the car will automatically turn left.
For a return dart, the automatic left turn depends on the force of the wind on its two rotating “wings”. In the process of returning the darts forward, each time it flips, it pulls itself back a bit, which creates a kind of pressure on the top of the back dart, which is the same as the weight on the wheel when the body leans left when riding a bicycle. The darts turned to the left side by little. As the darts are drawn back into an arc, it slowly descends, like a helicopter propeller, and finally falls under the owner’s feet.
The back dart is a flying stick. Archaeologists have found flying rods in the tombs of ancient Egypt, which means that they exist for at least 10,000 years. Some American Indians use them to hunt hares.
Unlike the return darts, ordinary flying sticks do not spin back after being thrown out. The flying rod that can be rotated back is from Australia. Before the aliens entered the Australian mainland, the indigenous people here were a nomadic group. They used the flying rods that could not be cycled to hunt, but they also invented the returning darts that could be rotated back. Some scientists believe that the original intention of Australian Aboriginal people to invent darts is to scare the waterfowl and make it to the net, but more people think that darts are a delicate toy.
Ordinary back darts are usually banana shaped and range in length from 40 cm to 1 m. The back darts made with plywood are now only 3 to 4 ounces, which is equivalent to the weight of two small packets of French fries.
The back darts are not necessarily banana-shaped, and the star-shaped, “H”-shaped and Indian tomahawk-shaped back darts can be rotated back after being thrown.