First, the five elements of leverage.
1, fulcrum: the point around which the lever rotates is called the fulcrum of the lever. It is represented by the letter o.
2. Power: The force acting on the lever to make it rotate is called power. It is represented by the letter F 1
3. Resistance: The force that acts on the lever and hinders the rotation of the lever is called resistance. Represented by the letter F2.
4. Arm of force: The distance from the fulcrum of lever to the line of action of force is called arm of force. It is represented by the letter l 1
5. Resistance arm: The distance from the fulcrum of lever to the line of resistance action is called resistance arm. Represented by the letter l2.
Second, understanding and mastering the five elements of leverage should pay attention to the problem
1. About the fulcrum: the fulcrum must be located on the lever. It may be at one end of the lever or in the middle of the lever. When the lever rotates, the fulcrum is relatively fixed. When drawing a lever diagram, the fulcrum should be marked with "△" and marked with the letter "O";
2. About force and resistance: Force and resistance are named according to the effect of force on rotation, both of which are external forces exerted on the lever, and the lever is a stressed object, so the action points of force and resistance are on the lever; Power point: the point at which power acts on the lever. Resistance action point: the action point of resistance on the lever.
Generally speaking, the force that people exert on the lever or make the lever rotate according to people's wishes is called power, and the force that prevents the lever from rotating in the required direction is called resistance. The directions of force and resistance are not necessarily opposite, but they make the lever rotate in the opposite direction;
3. Regarding the concept of the moment arm, it should be noted that the moment arm is the distance from the fulcrum to the line of action of the force, which is consistent with the distance from the point to the line in mathematics; Never understand it as: the distance from the fulcrum to the stress point! If a force acts on the lever, if its point of action remains the same, but the direction of the force changes, then the arm of force will generally change; The arm of force is not necessarily on the lever; If the line of action of force passes through the fulcrum, its arm of force is zero; In other words, it has no effect on the rotation of the lever.