"Measuring the Density of Matter" Mass and Density PPT Courseware 4

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"Measuring the Density of Matter" Mass and Density PPT Courseware 4

think about it

1.What is density?

The mass of a substance per unit volume is called the density of the substance.

2. What is the density of water? What is its physical meaning?

How to measure the density of a substance?

General methods for measurement experimental design

(1) Select relevant physical formulas according to the needs of measurement

(2) Select the measurement tool based on the physical quantity to be measured in the formula

(3) Be familiar with the use of measuring tools, and be able to measure and read data correctly, as well as perform calculations and data processing according to formulas

Understand measuring cylinders and measuring cups

Use a measuring cylinder to measure the volume of liquid. The water surface in the measuring cylinder is concave. When reading, the line of sight should be level with the lowest point of the liquid level in the measuring cylinder.

Example: Inject water into the measuring cylinder, and the reading from above is 20mL. After pouring out a part, the reading from above is 12mL. Then the volume of the poured water is ( )

A. Equal to 8mL B. Greater than 8mL

C. Less than 8mL D. Unable to determine

Analysis: When reading, look down at the scale, and the value read out will be larger than the actual value; when reading, look up at the scale, and the value read out will be smaller than the actual value. In this question, the first reading is from looking down, and the actual volume of water in the graduated cylinder is less than 20 mL; the second reading is from looking up, and the actual volume of water remaining in the measuring cylinder is greater than 12 mL; therefore, the volume of the water poured out is less than 8 mL. Choose C.

Use of measuring cylinder

The volume of liquid can be directly measured using a measuring cylinder.

For irregularly shaped solids, the volume cannot be measured using a scale. At this time, measurements can only be made using a graduated cylinder using the drainage method.

The specific method is: first pour an appropriate amount of water into the measuring cylinder, read the scale V1 corresponding to the water surface, then gently place or press the object to be measured into the water, and read the reading V2 at this time. V2-V1 is the value of the solid. volume.

Experiment: Determine the density of paraffin, which has a density less than water

Method 1: Press-in method

Equipment: balance, measuring cylinder, water, thin wire, paraffin

① Use a balance to weigh the mass m of the paraffin block

②Pour an appropriate amount of water into the measuring cylinder and record the volume V1 of the water.

③Put the paraffin into the water in the graduated cylinder, use a thin wire to press the paraffin into the water, record the scale value V2 reached by the water surface in the graduated cylinder at this time, the difference between the two readings V= V2-V1

④ Find the density of paraffin according to the formula ρ = m/v

Give it a try:

1. In an experiment to determine the density of small stones, a student’s experimental steps were as follows:

a. Use a balance to weigh the mass m of the stone;

b. Pour a certain amount of water into the measuring cylinder and record the volume V1 of the water;

c. Immerse all the stones in water and record the volume V2 of water;

d. Place the balance on a horizontal table and adjust the balance;

(1). The reasonable experimental steps are d, a, b, c; (indicated by letters)

(2) The calculation formula for the density of stones is ρ=m/v;

self-assessment

1. A classmate smashed a small piece of rock from a large uniform rock. The mass was weighed on a scale to be 27g. Put it into a measuring cylinder filled with 80mL of water. When the water level rises to 90mL, the density of this rock is _______kg/m3. The density of this small piece of rock is _______ with the density of that large piece of rock (optional "equal" or "not equal").

2. The mass of a small bottle is 78g, and the total mass when filled with water is 178g. Then the volume of this small bottle is _____cm3. In a measurement, first put a few solid particles into the empty bottle and weigh the total mass as 132g. Then fill the bottle with water and weigh the total mass as 212g. Then the density of this solid material is ______kg/ m3, it may be ________.

3. In order to use a balance and a measuring cylinder to measure the density of a wax block that cannot sink in water, a student conducted the following experiment: first use a balance to weigh the mass of a wax block as 18g, fill the measuring cylinder with 60cm3 of water, and then put the wax block Bundle it with a copper block with a volume of 10cm3 and put it into a measuring cylinder. When it is completely immersed in water, the scale on the water surface in the measuring cylinder is 90cm3. Then the density of this wax block is ( )

A. 1.8×103kg/m3 B. 0.9×103kg/m3

C. 0.6×103kg/m3 D. 0.2×103kg/m3

Regarding the question of looking up and looking down on the measuring cylinder:

When reading, the measuring cylinder should be placed on a horizontal table. When observing the scale, the line of sight, the scale line and the lowest point of the concave liquid level of the liquid in the measuring cylinder should be kept level. When looking at the volume of the measuring cylinder, look at the center point of the liquid level. If the liquid level is concave, the line of sight should be based on the bottom of the concave liquid level; if the liquid level is convex, the line of sight should be based on the top of the convex liquid level.

When looking down, the line of sight is slanted downward. The intersection point between the line of sight and the cylinder wall is on the liquid surface, so the data read is higher and the actual value is lower.

When looking up, the line of sight is slanted upward. The intersection point between the line of sight and the cylinder wall is below the liquid surface, so the data read is lower and the actual value is higher.

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Update Time: 2024-07-01

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