"Quality" Quality and Density PPT Courseware

"Quality" Quality and Density PPT Courseware

learning target:

1. Understand the concept of quality and master the units and conversion relationships of quality;

2. Know that the mass of an object does not change with the shape, state and position of the object;

3. Know the structure of the pallet balance and master the use of the pallet balance.

1. Quality

Stools, desks, hammers, and nails are called objects in physics, and the wood and iron that make up these objects are called "substances."

From the above observations, we can conclude that stools and desks contain different amounts of wood; hammers and nails also contain different amounts of iron.

1. Definition

The amount of matter an object contains is called its mass. Symbol m.

think about it

1. If a toothpaste wrapper is rolled up and its shape changes, will its quality remain the same?

2. A lidded container filled with ice cubes. All the ice in the container melts into water and its state changes. Does its mass remain the same?

3. If the camera is taken from the earth to the moon, will the quality of the camera change?

Quality is an inherent property of the object itself. It does not change with changes in the shape, state, geographical location and temperature of the object.

2. Unit of mass

In the International System of Units, the main unit of mass is the kilogram, with the symbol kg.

Commonly used mass units: tons (t), grams (g), milligrams (mg)

Conversion relationship:

1t=103 kg 1kg = 103g 1g = 103m g

2. Measurement of quality

Balances are commonly used to measure mass in school laboratories and factory laboratories. Commonly used balances include tray balances and student balances.

1. Structure of the balance

Self-study: Read the second part of the textbook to understand the construction and use of the balance.

2. Structure of pallet balance

3. Use of pallet balance

Before using the balance, please note:

① Check the weighing and graduation values ​​clearly. Weighing: Each balance has its own maximum mass that it can weigh, and the mass of the object being measured cannot exceed this maximum mass; graduation value (sense): the mass value represented by each small grid on the scale. (Look at the engraved lines on the left side of the game code)

② When adding or subtracting weights to the right plate, use tweezers, do not touch the weights with your hands, and do not get the weights wet or dirty;

③ Wet objects and chemicals cannot be placed directly on the balance tray. They should be weighed indirectly using a beaker or white paper.

④ Place the object to be weighed in the middle of the left pallet, use tweezers to pick up the weights in order from largest to smallest and place them in the middle of the right pallet;

⑤When the added weight is inappropriate, move the weight until the balance is balanced;

⑥The mass of the weight in the tray plus the indication of the weight is the mass of the object to be weighed.

Use a balance to measure the mass of a liquid

1. First measure the mass m0 of the empty bottle

2. Then measure the total mass m of the bottle and liquid

3. Subtract the mass of the empty bottle from the total mass of the bottle and the liquid to equal the mass of the liquid:

M thing = m total — m0

Measuring the mass of small objects using a balance (cumulative method)

1. Measure the total mass of multiple objects

2. Divide the number by the total mass to get the mass of a tiny object

When a full glass of water freezes, the ice bursts the glass. This is because when the water freezes ( )

A. The volume has increased. B. The mass has increased.

C. The volume and mass increased. D. The volume and mass both decreased.

In the following situations, the mass of the object changes:

A. A compressed spring

B. An object is moved from the moon to the earth

C. A piece of iron heated until it turns red

D. A tree that keeps growing taller

Which of the following statements is correct ( )

A. The mass of the lunar module decreases from the earth to the moon

B.1kg of iron has greater mass than 1kg of cotton

C. After the glass is broken, its quality remains unchanged.

D. After a glass of water solidifies into ice, its volume and mass also increase.

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