Doubts about the balance of the balance 15

The equilibrium state in kinematics is a constant linear motion or a state of rest, and does not include a constant rotation around the axis. That's number one. Second, the balance is different from other weighing tools, it is a structure with equal arms at both ends, only when the weight of both ends is equal, and when the weight of both ends is unequal, it is unbalanced, that is, one end is high, and one end is low.

These two "balances" are not the same concept, and if they are put together, they will be suspected of stealing beams and changing pillars. The definition of equilibrium is good, saying that an object is in equilibrium is for a specific object, for example, a rope is hung on the ceiling, and a steel ball is hung at the lower end of the rope, when the rope and the steel ball are stationary, we can say that the steel ball is in equilibrium, it is balanced by its own gravity, air buoyancy (negligible), and the hanging force of the rope, or it can be said that the rope is in equilibrium, it is balanced by its own gravity, the pulling force of the steel ball on it, the air buoyancy (negligible) and the ceiling hanging force on it. For the balance, "when one end of the balance is low and the other end is high, when it is stationary", at this time it is in a state of equilibrium for the beam of the balance, which is balanced by the tension of the two weight discs and pendants at both ends, its own gravity, the support force of the knife edge to it, etc.

However, it is unbalanced for the balance as a whole, because the definition of balance balance is "when the crosshead pointer points to the balance zero point in the middle, and the beam is in a state of propping, then it is called balance balance, which is the definition of balance balance determined by its working principle". The two balances have different meanings.

You are right, when the resultant external force on an object is zero, it is indeed in equilibrium, and this is for the object. But when it comes to the balance, we say it's unbalanced because it weighs unequal at both ends. If you look at the balance as a whole, it is stationary and indeed in equilibrium, but because it is not equal at both ends, it is not balanced at both ends!

The definition of equilibrium you say is force balancing.

The balance is low at one end and high at the other end may be due to some damping at the shaft, in which case the balance and force (mass) are not equal.

Strictly speaking, when one end of the balance is high and the other end is low, the arms at both ends are not equal. It is also in equilibrium at this time, but the mass of the matter at both ends is not equal.

Adjustment method: 1. When the left end of the balance is raised (the pointer is biased to the right), the balance nut of the left balance is adjusted to the left until the pointer points to the center line of the index dial;

2. When the right end of the balance is raised (the pointer is biased to the left), the right balance nut of the balance is adjusted to the right until the pointer points to the center line of the index dial.

3. Only the right balance nut (some balances have balance nuts on the left and right), but it can be rotated inward and outward, and the balance is inclined to outward rotation on the left and inward on the right.

4. The main thing is to balance the balance or other measuring tools (such as rod scales also have balance nuts) to make the measurement accurate.

5. Reading = weight quality + number of code (when the left object is right), reading = weight quality - number of the code (when the left code is right).

This indicates that the balance is balanced. There are three states of balance in balance: casual balance, stable balance, and unbalance.

When the balance is in casual balance, the center of gravity of the balance is higher than the fulcrum;

When the balance is stable and balanced, the center of gravity of the balance coincides with the fulcrum;

When the balance is unstable and balanced, the center of gravity of the balance is lower than the fulcrum.

Balances need to be in a state of stable equilibrium in order for us to weigh objects accurately.

The balance is equivalent to an equal-arm lever because of the grinding of the two side arms.

Equal, according to the conditions of lever equilibrium: l1·f1=l2·f2, l1=l2, so when the balance is balanced, the gravitational force on the objects in the pallets on both sides is equal, that is, the mass of the object is equal to the weight mass.

Libra: Too indecisive! The grass on the wall will inevitably lead to the loss of opportunities, and there will be no defeat and balanced development without a decision! Libra always wants to see the positive and negative sides of the problem, so they will carefully examine it from different angles

A balance is a measuring tool.

The balance is an instrument to measure the mass of the object, made according to the principle of the lever, there is a small plate at each end of the lever, one end of the weight, the other end of the object to be weighed, the lever ** is equipped with a pointer, when the two ends are balanced, the mass (weight) of both ends is equal.

According to papyrus, the Egyptians used scales as early as more than 1500 BC. Other scholars say that it may have been earlier than that, about 5,000 years ago. Although the ancient Egyptian balance was very rough, it already had the outline of the modern balance and became the prototype of the modern balance.

In ancient China, there were also instruments with a balance structure, which were produced earlier. By the late Spring and Autumn period, the manufacturing technology of balances and weights was quite sophisticated. The bamboo piece is used as the beam, the silk thread is the button, and a copper plate is hung at each end.

Later, because the balance weighed objects was more troublesome, it was changed to "Quan", and the balance was used when weighing small objects.

After adjusting the balance nut, the mass of the left and right discs is equal, and when measuring the mass of the object, the mass of the left and right discs is also equal, which does not affect the measurement results.

Tray balance readings retain 1 decimal place, which is required for the accuracy of the instrument. Pallet balance is a kind of weighing tool commonly used in the laboratory, which is composed of tray, beam, balance nut, scale, pointer, knife edge, base, ruler, vermetro, weight, etc.

The sum of the mass of the weight in the right disk and the indication of the code on the ruler is the mass value of the measured object!

If only (weight + code can be estimated), then the error comes from the code estimation, if it is (weight + code + pointer reading), then the error comes from the pointer reading, you can think like this, when the balance is balanced, if the code is a small distance to the side, then the pointer will be a large distance, so (weight + code + pointer reading) is more scientific.

1 Installation of the balance.

Wipe the parts of the balance clean with cotton yarn and install them as required, noting that the parts on the left and right sides of the beam cannot be interchangeable (left "1" and right "2"); Use the stop knob to make the beam rise and fall several times, adjust the beam support spiral, so that the beam does not twist when it rises and falls, and the middle knife edge can leave the middle knife bearing after falling, and the balance plate just falls on the base.

2 Adjustment of the balance.

Adjust the level of the bottom plate: adjust the screws of the bottom plate to make the bottom plate level (check with the heavy vertical line or bubble level).Before adjustment, the teacher can raise the left, right, front and rear ends of the base plate respectively, so that students can observe the relative position of the weight and the small cone at this time, so as to understand how to adjust the screws.

When adjusting, you can adjust the left and right levels first, and then adjust the front and back levels.

Adjust the balance of the beam: Move the code to the zero scale line of the beam, and adjust the balance nut of the beam to make the beam balanced. Care should be taken to use the stop knob when adjusting, and it should be emphasized that the hands are always biased towards the less mass side.

3 Use of Balances.

1) According to the general custom, the object to be measured is placed on the left plate, and the weight is placed on the right plate.

2) Turn the stop knob with the left hand to lift the balance, and use tweezers to add or subtract weights with the right hand, paying attention to estimating the mass of the object first, and then adding or subtracting the weights in order from large to small.

3) After the balance is balanced, the total mass of the weight is read out and the mass shown in the weight is added. The weight can be taken out while the weight is taken and the quality of the weight taken can be noted at the same time.

4) For objects with a mass of less than 1 gram, they can be weighed directly with a free code.

Precautions] 1 Several issues that need to be paid attention to: (1) the maximum reading of the vernier scale and the weighing value of each grid, and the baseline of the vernier code reading (generally the left side of the vernier code); (2) a method for adjusting the level of the bottom plate with a bubble level; (3) Maintenance of the balance.

2 Mistakes that students make when using scales: (1) reversing the order of adjusting levels and balances; (2) The balance after adjusting the level can move the position at will; (3) When adjusting the balance, the code is not placed in the zero position; (4) Do not follow the order from large to small to choose weights; (5) Mutual borrowing and exchanging weights between groups.