Experimental process of leverage

The design lever is a simple machine that uses a straight rod or a curved rod to rotate around the fixed point-fulcrum on the rod under the action of external force. This experiment guides students to understand the following functions of lever:

(1) the function of transmitting force;

(2) the function of changing the direction of force;

(3) the function of saving labor (but distance) or distance (but saving labor). In order to make students aware of these effects, it is best to choose a heavier object and let students pry or lift it with a lever. In addition, some quantitative experiments can be carried out with lever ruler and dynamometer.

Method one

The equipment is a schoolbag full of learning tools, a wooden stick with a length of about 1 m (divide the wooden stick into 8 ~ 10 and draw an equal line), and a chair.

step

(1) Put the middle of a wooden stick on the backrest of a small chair, hang a heavy object-schoolbag at one end, hold it with your hand at the other end, press it down slowly, and pry the schoolbag up. Guide students to find the fulcrum, stress point and key point of lever.

(2) Press the stress point hard, and the force will be transferred to the other end of the lever through the lever to pry up the heavy object. This shows that the lever has the function of transmitting force and changing the direction of force.

(3) Make the fulcrum close to the key point. Every time the fulcrum moves forward, pry it once or twice Every time you pry an object to the same height, you will feel that the closer the fulcrum is to the key point (that is, the farther the fulcrum is from the force point), the more effort you need, but the longer the hand (force point) moves, the more distance you need.

(4) Make the fulcrum close to the stress point. Move the fulcrum back one square and pry it once or twice. Every time you pry an object to the same height, you will feel that the closer the fulcrum is to the force point (that is, the farther the fulcrum is from the key point), the more effort it will take, but the shorter the distance the hand (force point) moves, the more distance it will save.

Method 2

Two lever rulers are used for the equipment (divide the lever ruler into 12 grids evenly, and make a hole in each grid), a ruler, a dynamometer, a hook code and a line hook.

step

(1) Pass the nail of the bracket through the sixth hole position of two lever rulers (the hole position is counted from left to right), and use this as a fulcrum to keep the two lever rulers horizontal. The lever ruler at the back doesn't move. As a control, the weight and dynamometer are hung on the front lever ruler.

(2) At the 1 hole of the lever ruler, hook 50 grams of hook code with iron wire; Hang the dynamometer hook at the 1 1 hole of the lever ruler, and hold the dynamometer in your hand and pull it down hard, so that the weight (hook code) can be pried up. Find out the key points, fulcrums and stress points on the lever ruler. (Hook code 1 hole is the key point, the sixth hole in the middle is the fulcrum, and the dynamometer 1 1 hole is the stress point. )

(3) The downward force of the dynamometer can pry up the weight, which shows that the lever has the function of transmitting force and changing the direction of force. Observe the reading of the dynamometer, about 50 grams, indicating that it is neither labor-saving nor laborious at this time. Using a ruler to measure the rising distance of the key point and the falling distance of the stressed point, it can be seen that the rising and falling distances are roughly equal, indicating that the distance is neither saved nor wasted at this time (Figure 1).

(4) Without changing the positions of key points and stressed points, observe the lifting distance between the readings on the dynamometer and the key points and stressed points when the fulcrum moves to the 5th, 4th, 3rd and 2nd holes, and pry up the heavy objects (the height is the same each time). Through the above experiments, we can know that the closer the fulcrum is to the key point (and the farther the fulcrum is from the stress point), the smaller the reading on the dynamometer is, the more labor-saving it is; The greater the distance that the force point falls than the distance that the key point rises, the more time it takes (Figure 2).

(5) Without changing the positions of key points and stressed points, observe the lifting distance between the reading on the dynamometer and the key points and stressed points when the fulcrum moves to the 7th, 8th, 9th and 10 holes, and pry up the heavy objects (the lifting height is the same every time). Through the above experiments, we can know that the closer the fulcrum is to the force point (and the farther the fulcrum is from the key point), the greater the reading on the dynamometer, the more laborious it is; The smaller the distance that the force point falls than the distance that the key point rises, the more distance is saved.