"Quality and Its Measurement" Quality and Density PPT Courseware

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"Quality and Its Measurement" Quality and Density PPT Courseware

All objects are composed of matter, and they vary in size, shape, and amount of matter contained. In this chapter we have a preliminary understanding of the quality of matter.

Mass of an object and its measurement:

What materials is the table made of? Wood, iron, paint.

What materials are the small iron spoons and iron pots made of? Made of iron.

Plastic rulers and plastic boxes are made of plastic.

There are various objects around us, such as spoons, pots, rulers, boxes, tables, chairs, etc.

And these objects are all composed of the iron, plastic, wood, glass and other substances we just mentioned. All objects in nature are composed of substances.

1. Quality:

(1) Definition: The amount of matter contained in an object is called the mass of the object. Represented by the letter (m);

(2) The matter contained in an object belongs to the object. Every object has mass. For a given object, what if certain factors change and the mass remains unchanged?

Since the amount of matter contained in these objects has not changed, the mass of the object remains unchanged, that is: the mass of the object is an attribute of the object itself and has nothing to do with changes in the shape, state and location of the object.

If it contains a lot of material, it has a large mass, if it contains a small amount of material, it has a small mass. To compare the mass of two objects, there must be a standard, that is, to determine its unit mass.

(3) The unit of mass in the International System of Units is the kilogram (kg), which is what we usually call 1 kilogram. People stipulate that the mass of 1 liter of pure water at 4°C is 1 kilogram. Think about 1 kilogram objects in life: for example, two medium-sized bottles of mineral water have a mass of about 1 kilogram; two large bags of Mengniu milk packed with Tetra Pak pillows, and 20 ordinary eggs have a mass of about 1 kilogram. Commonly used units: tons (t), grams (g), milligrams (mg), micrograms (ug). The relationship between them: 1t=103kg, 1kg=103g, 1g103mg, 1mg 103ug. These units are used in different situations. , such as: the load capacity of cars and trains, the output of grain, steel, and coal, the quality of pharmacies, laboratories, and pharmaceutical preparations.

2. Measurement of quality:

How to measure the mass of an object? Common quality measuring instruments in life:

Bench scales, scales, electronic scales, steelyards, as well as physical balances and pallet balances for laboratories.

We mainly learn how to use the pallet balance:

(1) First, we compare the diagram to understand its structure.

And analyze the function of each part.

① Base: support and placement.

② Tray: holds items and weights.

(Generally, left things are coded right, why is left to you to think about)

③Beam, knife edge, and pointer: the three are connected into one, and they interact together to indicate whether the balance is balanced.

Since the support point of the knife edge is very small, the ∴ response is very sensitive. If the left and right masses are slightly different, the beam will swing, causing the pointer to deflect.

The left sinking deflects to the left, the right sinking deflects to the right.

④ Index sign: Check whether the balance is balanced. If the pointer swings to the left and right in the center of the index sign with equal amplitude, or the pointer exactly points to the central scale line and the beam is stationary, it means the balance is balanced.

⑤Balance nut: Adjust the balance of the balance.

⑥Weighing scale (Vernier scale), Vernier scale: When measuring the mass of an object, sometimes it is necessary to move the position of the vernier scale to the right.

⑦ Weight box: weights and tweezers, among which there are one weight of 100 grams, one weight of 50 grams, two weights of 20 grams, one weight of 10 grams, and one weight of 5 grams.

(3) Now you can measure the mass of the object.

①Left object: Place the object to be measured gently in the left plate.

②Right weight: We need to estimate the mass of the object. First use tweezers to pick up the large weight, place it in the right plate, and then add the smaller weight.

③Movement code: Use tweezers to lightly pluck the movement code so that the pointer swings at the same amplitude (number of grids) on both sides of the central scale line, or stops on the central scale line, which is balanced again.

④Reading: At this time, the mass of the object is equal to the sum of the total mass of the weights in the right pan and the reading on the vernier scale.

NOTE: A balance is a precision measuring tool.

① Move and operate gently; ② Use tweezers when picking up and placing weights; ③ Do not exceed the weighing range of the balance; ④ Keep the balance clean and dry, and when weighing corrosive substances, place paper on the plate or place it in a container Weigh.

(Paper paper: two sheets of the same size, placed on the left and right plates respectively)

(Container: The mass of the container needs to be weighed first).

Example 1: A classmate uses a pallet balance to weigh the mass of a grain of rice. His steps are:

(1) Place the balance on a horizontal platform and place the cursor at the zero mark on the left end of the ruler;

(2) Place a grain of rice in the right pan of the balance, add or subtract weights to the left pan, and adjust the position of the scale on the scale until the balance beam is balanced;

(3) The total mass of the weights in the plate plus the scale corresponding to the free weight on the scale

The value is equal to the mass of a grain of rice.

Which step did this student miss?

What operations are incorrect?

Analysis: When using a pallet balance, you must first place the balance on a horizontal platform, adjust the balance so that the beam is balanced to measure the mass of the object. When measuring the mass, the object to be measured can only be placed on the left plate and the weight on the right plate. When using, pay attention to the maximum weighing and minimum weighing of the balance. If the mass of the object being measured is estimated to be greater than the maximum weighing of the balance, the balance cannot be used to weigh the object; if the mass of the object being measured is estimated to be less than the minimum weighing of the balance For weighing, we need to adopt a flexible method and use the commonly used accumulation method to measure the mass of small objects. That is, weigh the total mass of several identical objects and then divide it by their number to obtain the mass of a single measured object. .

Several special methods of quality measurement:

(1) Cumulative method: used to measure the mass of a single solid with a small mass that is not easy to measure directly. Accumulate the tiny units to be measured, take a few and write down the number n, and measure the total mass M of several units, then: the mass of each small unit m = M/n

(2) There is an error when measuring the mass of an object with an unequal arm balance. When the left arm is long, the measurement value is larger, and when the right arm is longer, the measurement value is smaller. Correction method: First put the object to be measured into the left pan, and when the weight m1 is placed on the right pan, the balance will be balanced, then: m2gl left = m object gl right. When the object to be measured is placed in the left pan, and the weight m2 is placed on the right pan. When the balance is balanced, the two equations are divided and we get: m object gl left = m1gl right

∴ ∴m2 object m1 m2 ∴m object=√m1m2

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Update Time: 2024-09-29

This template belongs to Physics courseware Lu Jiao edition eighth grade physics volume 1 industry PPT template

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