Note: This experiment is dangerous, please accompany your parents to complete it. Compound bows are powerful, so be sure to keep your surroundings open and safe when playing, and never shoot at anyone or anything!
Late one night
The brothers and sisters in the office ordered a barbecue together
Look at the used disposable chopsticks
I suddenly wanted to make a toy out of it
Ask my sister to borrow a head rope and a utility knife
Ask my brother to borrow a ruler and a pencil
Grab the needle-nose pliers and paper clips from the lab
Make a little toy for competition
So the office is happier
……
Experimental equipment
Two pairs of disposable chopsticks, two rubber bands, two head ropes, two paper clips, utility knives, rulers, pencils, needle-nose pliers, and the labeled cups
Experimental Procedure
Step 1:
Cut a pair of chopsticks into two wooden sticks of about 15 cm, and carefully smooth the thorns at both ends with a utility knife.
Step 2:
Take the other two chopsticks, divide them in two, take half of the chopsticks, and place them between the two chopsticks obtained in the first step as shown in the picture. Make a hole with a utility knife at the marked position (about 1 cm from the edge). Both sides operate symmetrically in the same way. Tips: Use the tip of the knife to rotate back and forth from the front and back to punch the hole, and finally open it up~
Step 3:
Straighten the paper clips through the holes, cut off the excess at both ends with sharp pliers, and twist them into a circle. Do the same thing symmetrically on the other side.
Step 4:
Mark about 1 cm from the edge of the picture, and use a utility knife to make a groove at the short end on the left and a circular groove at the long end on the right.
After that, turn it over and make four grooves in the mark in the back view (where it is on a perpendicular plane to the front groove).
Step 5:
Wrap the two head ropes three to four times around the middle groove. Tie two rubber bands together and tie them to the annular grooves at both ends. (It is possible to use the fisherman's knot method, i.e. to pull a loop from the middle of the rope loop)
If the elasticity is not suitable and causes the bow to reverse, it can be adjusted by changing the length of the rubber band and the number of turns of the head rope.
In this way, a simple compound bow is ready! You can use the remaining chopsticks as "arrows", use foam and cardboard boxes to make a simple target, and compete with your friends in archery!
Note: Compound bows are powerful, so be sure to keep your surroundings open and safe when playing, and never shoot at anyone or anything!
Hara explained
This "compound bow" is actually more like a slingshot, using three rubber bands to provide elastic power.
Most rubber band products on the market are within 4.5 times the drawing distance, and the relationship between the tensile force and the drawing distance approximately satisfies Hooke's law F=kx, that is, the force and the deformation meet the linear relationship. Therefore, to give the rubber band a tensile force, the elastic potential energy accumulated by the elongation of the rubber band is
E=kx/2,
where k is the elastic coefficient and x is the elongation of the band.
After letting go, the elastic potential energy of the rubber band is converted into the kinetic energy of the arrow, by the formula
E=mV/2
You can get the initial velocity V of the arrow, adjust the angle of the shot, and you can shoot different trajectories (flat throw, oblique throw, can be counted as a dozen high school physics problems).
Regardless of the influence of the shape of the arrow, the trajectory can be approximated as a ballistic curve, which can be calculated using the simplest particle ballistic model in ballistics. You can also silently do mental arithmetic when archery to determine how to shoot arrows to "hit the bull's-eye"~
Schematic diagram of the ballistic curve of a steel ball with a diameter of 8 mm with an initial velocity of 100 m/s launched at an elevation angle of 31 °
* Design & Inspiration: bilibili up master: @x little bully x
Edit: Play seriously