How long is a cross tire wrench in life? Today we will […]
How long is a cross tire wrench in life? Today we will take a look at the tire cross wrench manufacturer. According to the principles of physics, the longer the lever, the more labor-saving. In actual use, the appropriate length should be selected so that it is easy to use.
We all know that Archimedes once said: "Give me a foothold and a lever long enough, and I can move the earth." However, while defending the ancient city of Syrah, he charged a few The soldier who used the lever to move the stone yelled: "Don't use such a long lever for a short one." Why is this? The soldiers were stunned. How can I use short leverage? Don't you need to work hard? But the king commanded: Believe everything Archimedes has said, and have to do what he believes and disbelieve, and it saves more effort than using a long lever. The soldiers were puzzled and prepared to consult Archimedes afterwards. Unfortunately, because the castle was broken by the enemy, Archimedes was killed by Roman soldiers before he could answer the questions of the soldiers. Let us help Archimedes complete this task.
It turns out that when we usually study levers, we mainly focus on light levers, that is, without considering the lever's own weight, so the longer the lever, the larger the power arm can be adjusted to save effort. But when the weight of the lever is taken into account, the situation has also changed, which we illustrate through typical data calculations.
Example: There is a uniform lever with a weight of 40 Newtons per meter, which can be rotated around point O. To pry a rock weighing 490 N at a distance of 0.5 meters from the fulcrum, and ask how long the lever should be, it will act on the lever. The force at the other end is minimal.
Analysis and settlement: Set the lever length to L, then the fulcrum of this lever is O, the force F1 at end A is the power, and the power arm is L; the resistance has two parts: the lever itself weight G=L×40 N, and its force arm is L/ 2; The pressure of the pried stone on the lever B is F2=490N, and the force arm is OB=0.5m. According to the principle of leverage balance: F1L=40L×L/2+490×0.5 F1=20L+245/L According to mathematical knowledge, F1 has a minimum value when 20L=245/L. The solution is: when L=3.5m, F1 minimum=140N
It can be seen from the calculation that the lever is the most labor-saving when the length is 3.5 meters, and when the lever is greater or less than 3.5 meters, the force used is greater. The levers we usually use have a heavier weight, so in actual use, we must choose the appropriate length, not the longer the better.