"The Mass of Objects" Materials Around Us PPT Courseware

Description

"The Mass of Objects" Materials Around Us PPT Courseware

learning target

1. Understand the concept of quality and its units. Know that mass is a fundamental property of objects

2. Be able to form a perceptual understanding of mass units and estimate the mass of common objects.

3. Be able to correctly use a pallet balance to measure the mass of solids and liquids

Core test points: attributes and estimation of mass, use of pallet balances.

Preview before class

1. The amount of _______ contained in an object is called mass, represented by the letter _____. Its international unit is _____. Commonly used units include _____ and _____.

2. Please fill in the correct unit after the following data:

(1)The mass of a middle school student is about 50____

(2)The mass of a one-yuan coin is about 5____

(3)The mass of an elephant is about 6___

(4)The mass of a pin is about 80_____

3. When an astronaut with a mass of 60kg reaches the moon, his mass will _____ (optional to increase, decrease or remain unchanged).

4. _______ is commonly used to measure quality in the laboratory, and _______, _______, _______, etc. are commonly used to measure quality in life.

5. When using a balance to measure mass, you should first place the balance on the _______ work surface. When measuring, place the left pan on the _______ and the right pan on the _______. Use _____ to pick up and place the weights. The mass of the object to be measured cannot More than _____ on the scale.

Lectures in class

Knowledge point 1. The concept of quality

All objects in nature are composed of matter. For example, a hammer and a nail are both composed of iron, but the amount of iron they contain is different. A hammer contains more iron than a nail. Physics The amount of matter contained in an object is called the mass of the object, and its symbol is m.

When an iron block is pressed into an iron sheet, the shape changes, but the amount of iron contained remains the same, so the mass remains unchanged. When a piece of ice melts into water, the state changes, but the mass remains the same. A can, no matter where it is placed on the earth Its mass will not change wherever it goes or is taken into space by astronauts. The mass of an object does not change with changes in shape, state, and position.

[Example 1] (2014·Shantou) Astronauts brought an object with a mass of 50kg on the earth to the moon. At this time, the mass of the object ( )

A. Increase B. Decrease c. unchanged D. unconfirmed

[Exercise 1] (2014•Yichang) Which of the following statements about quality is correct ( )

A. When water turns into ice, its mass increases

B． The quality of physics books in Beijing and Shanghai is the same

C. 1kg of cotton has less mass than 1kg of iron

D． When an iron block is pressed into a discus, its mass decreases

Knowledge point 2. Units and conversions of mass

To compare the mass of an object, you must first determine the unit of mass. In the International System of Units, the unit of mass is the kilogram, represented by the symbol kg. The mass of 1dm3 pure water is approximately 1kg. The international standard kilogram is a platinum A cylinder made of iridium alloy, as shown in the figure below.

For convenience of use, the unit ton (t) larger than the kilogram and the unit gram (g), milligram (mg), microgram, etc. smaller than the kilogram are usually used. The conversion relationship between them is:

1t=1000kg=103kg, 1kg=1000g=103g,

1g=1000mg=103mg, 1mg=1000 =103

Written in the overall form: 1kg=10-3t=103g=106mg=109

[Example 2] (2014•Jinan) As shown in the picture, there is a "weighing scale" produced abroad. What is interesting is that the dial of this "weighing scale" is not marked with numbers but with some animals. When a middle school student uses this "scale" to measure his weight, the pointer of the "scale" will point to ( )

A.Cat B.Sheep C.Cow D.Elephant

[Exercise 2] An object with a mass of 150g may be ( )

A. A ping pong ball b. a pencil

C. an apple d. a shot put

Knowledge point 3. How to use and pay attention to the pallet balance

To accurately know the mass of an object, it must be measured with a measuring instrument. A commonly used measuring instrument in school laboratories is a pallet balance. Its structure is shown in the figure below. It mainly consists of a base, a dividing plate, a beam, a pointer, and a weighing scale. , balance nut, balance weight, tray, etc. Each balance has a box of matching weights.

The usage methods of the pallet balance can be summarized as: placing, dialing, adjusting, measuring, reading, and collecting.

Before using a pallet balance, you need to adjust it before measuring. The specific method is:

(1) Place: Place the balance on a horizontal table in an easy-to-operate place so that it is in a horizontally balanced state.

(2) Dial: Use tweezers to gently dial the cursor to the zero mark on the left side of the ruler.

(3) Adjustment: Adjust the balance nut on the beam so that the pointer points to the central scale line of the indexing plate. The method to adjust the balance nut is: adjust the balance nut in the opposite direction of the pointer, that is, when the pointer is to the left, adjust the nut to the right, and when the pointer is to the right, adjust the nut to the left, as shown in the figure below, at this time the pointer is to the right, so The balance nut should be adjusted to the left.

(4) Measurement: After adjusting the balance, you can measure the mass of the object. The measurement method is: when weighing, place the object to be measured on the left pan. After estimating the mass of the object to be measured, use tweezers to press the "First" button. Try adding weights one by one to the right in the order of "bigger, then smaller". If all the appropriate weights have been used and the balance is still unbalanced, use tweezers to gently move the scale to make the pointer swing on both sides of the central scale line by an amount of ( (number of grids) are basically the same, or remain stationary on the central scale line. It should be noted here: during the measurement process, the nut cannot be adjusted; when placing objects and weights, they must be "left and right", and when adding weights, they must be "bigger first and then smaller".

(5) Reading: The mass of the weight in the right pan plus the reading of the wandering code on the scale is equal to the mass of the object being measured in the left pan. The unit must be written in the measurement result. Students should pay attention: when reading the reading of the running code, the left side should prevail. As shown in the figure below, the reading of the running code should be 2.4g.

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Update Time: 2024-11-20

This template belongs to Physics courseware Guangdong and Shanghai version of eighth grade physics volume one industry PPT template

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