Experimental breakthrough one measures the density of solids
Proposition point
【Design and conduct experiments】
1. Experimental principle
(ρ=m/v )
2. Use and reading of the balance
3. Use and reading of graduated cylinders
4. Experimental step correlation analysis: The experimental procedure is as follows (ρ
thing
>ρ
water
, and insoluble in water)
(1) Use the balance to measure the mass m of the object
(2) Pour an appropriate amount of water into the vector cylinder and read the number V
1
(3) Tether the object with a string,
Slowly submerge the object in the water of the graduated cylinder
，
The number of the readout graduated cylinder is V
2
【Analyze data and phenomena and summarize conclusions】
5. Design tables to record data
Form design
6. Object density calculation or expression derivation (ρ=m/(V
-V
))
【Communication and Reflection】
7. Experimental error analysis
8. Special method to measure density
Experimental breakthrough two Measure the density of liquids
4. Design, supplementation and sequencing of experimental procedures
(1) Measure the total mass m of the liquid and beaker with a balance
(2)
Pour part of the liquid from the beaker into the graduated cylinder
, read the indicator V of the graduated cylinder
(3) Use the balance to measure the total mass m of the beaker and the remaining liquid
, the mass of the liquid in the graduated cylinder is m
－m
5. Design a table to record data
6. Calculation of density or derivation of expressions
(ρ＝(m1-m2)/V)
Experimental error analysis and special methods to measure density
1. Experimental error analysis
1. Causes of errors:
If the mass and volume measurement is inaccurate, the density can be judged to be large and small according to ρ=.
2. Solid density error analysis:
(1) Quality causes:
Measure volume first and mass later. If the solid is stained with water, the m is too large, resulting in ρ being too large.
(2) Volume caused:
For example, when measuring the volume by drainage method, the water surface of the overflow cup does not reach the highest position when the object to be measured is not put in, so that V is too small, resulting in ρ being large.
3. Liquid density error analysis:
(1) Volume causes:
The mass is measured first, and the volume is measured later, such as liquid on the beaker, so that V is too small, resulting in ρ being too large
(2) Quality causes:
The volume is measured first, and the mass is measured later, such as liquid on the measuring cylinder, so that the m is too small, resulting in ρ being too small
4. Ways to reduce errors:
Correct use of measuring instruments, reasonable adjustment of experimental procedures, etc.
Second, special method to measure density
Type 1 measures the density of a solid
1. A lack of balance measures the density of a substance
Figure 1
The mass of the solid to be measured is calculated using Archimedes’ principle:
G when floating
＝F
float
＝G
row
＝ρ
gV
→ measured with a graduated cylinder the volume of boiled water discharged when the solid floats (as shown in Figure 1), V
＝V
－V
； If the solid is pressed by a fine needle and submerged in water, the indicator number of the graduated cylinder is V
3
, then ρ
solid
＝ ρ
2. The missing measuring cylinder measures the density of the substance
Figure 2
(1) Overflow method:
As shown in Figure 2, the mass of the boiled water discharged when the solid to be tested is submerged with a balance m = m
，V
drain
＝ (m
-m
)/ρ
； If the mass of the solid is m
0
．
Figure 3
(2) Use Archimedes’ principle to calculate the volume of the solid to be measured:
V when submerged
/ρ
g→F
=Δmg→ The indicator number m of the balance before and after the solid is immersed in water is measured with the balance
、m
(as shown in Figure 3), Δm=m
, the volume of the solid is V
If the mass of the solid is m, then the density of the solid is ρsolid = mρ water / (m
) ．
Type 2 measures the density of liquids
Measure the density of the liquid to be measured using the floatation method:
Solids with less density are floated in the liquid to be measured and in water, respectively
Floating
Float
→ρ
liquid
Drainage
→ measured the volume of water and the liquid to be measured when the solid floats with a graduated cylinder (as shown in Figure 4).
ρ
/
＝(V
)ρ
/(V
Figure 4
Equal volume method:
As shown in Figure 5, the mass m = m of water equal to the volume of liquid to be measured is measured with a balance
＝(m
)/ ρ
Liquid density ρ
) ρ
Water/
(m
)．
Figure 5
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Proposition point
【Design and conduct experiments】
1. Experimental principle
(ρ=m/v )
2. Use and reading of the balance
3. Use and reading of graduated cylinders
thing
water
water
water
water
water
water
water
water
water
water
water
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
【Analyze data and phenomena and summarize conclusions】
Form design
-V
-V
【Communication and Reflection】
7. Experimental error analysis
8. Special method to measure density
－m
－m
－m
－m
－m
－m
1. A lack of balance measures the density of a substance
＝F
＝F
float
float
row
row
row
＝ρ
gV
gV
＝V
＝V
＝V
3
3
3
3
, then ρ
solid
solid
solid
solid
＝ ρ
2. The missing measuring cylinder measures the density of the substance
，V
，V
drain
drain
＝ (m
-m
-m
)/ρ
) ．
liquid
liquid
Drainage
＝(m