mass, volume, & density -...
TRANSCRIPT
Mass, Volume, & Density
MassMeasurement of the amount of matter
(or stuff) in an object
– Measured in grams (g)
There are 3 states
of matter:
Solid
Liquid
Gas
There are 3 states
of matter:
Solid
Liquid
Gas
Density is defined as mass per unit volume. It is a measure
of how tightly packed and how heavy the molecules are in
an object. Density is the amount of matter within a certain
volume.
Density
To find the density
3- Divide Density = Mass g
Volume cm³
1- Find the mass of the object
2- Find the volume of the object
1- Find the mass of the object
ALWAYS
REMEMBER
UNITS!
1) Find the mass of the object
2) Find the volume of the object
3) Divide : Density = Mass / Volume
To find density:
Ex. If the mass of an object is 35 grams and it takes up 7 cm3
of space, calculate the density.
Let’s try some density problems together
Work on these problems with your
neighbor
1 Frank has a paper clip. It has a mass of 9g and a volume of
3cm3. What is its density?
2. Frank also has an eraser. It has a mass of 3g, and a volume
of 1cm3. What is its density?
3. Jack has a rock. The rock has a mass of 6g and a volume of
3cm3. What is the density of the rock?
4. Jill has a gel pen. The gel pen has a mass of 8g and a
volume of 2cm3. What is the density of the gel pen?
Change Mass AND Keep Volume Same
Increase the mass increase density
Decrease the mass decrease in density
Which container has more density?
A B
Ways to Affect Density
Change Volume AND Keep Mass Same
Increase the volume decrease density
Decrease the volume increase density
Which container has more density?
A B
Ways to Affect Density
In your notebook illustrate the answer to
the following question:
What 2 ways will INCREASE density?
What 2 ways will INCREASE density?
Keep the
same
mass AND
decrease
the
volume
Keep the
same
volume
AND
increase
the mass
If you have 2 or more
substances,
the MORE dense
substance will be on
bottom
The LESS dense substance
will be on top
Liquid Layers – Try with your
neighbor
• Which liquid has the
highest density?
• Which liquid has the
lowest density?
Liquid Layers
Try on your own!
Imagine that the
liquids on the right
have the following
densities:
– 15g/cm3 10g/cm3
– 3g/cm3 9g/cm3
– 7g/cm3 12g/cm3
Match the colors to
the correct densities.
3g/cm3
7g/cm3
9g/cm3
10g/cm3
12g/cm3
15g/cm3
Super Scientist
Question of the Day
• Jake has a book, a ruler, and a balance.
• How can Jake find the density of the
book with the tools he has?
Reading Equipment
• Precision – How close two or more
measurements are to each other
• Accuracy – How close a measurement is to
its standard or known value.
1. You are measuring the boiling point of
water without salt. Your three
measurements are 80.1 oC, 80.6 oC and
79.8 oC.
2. You take three more measurements and
measure 100.4 oC, 99.8 oC and 100.0 oC.
Examples: Precise or Accurate
Accurate and Uncertain
• When measuring a numerical value, you can only be so
certain.
– Your uncertain value is the value one decimal place to the right of
your certain value.
– What is the uncertain decimal place for the thermometers below?
Uncertainty in Measurement• All measurements have a degree of uncertainty regardless
of precision or accuracy.
• Uncertainty is caused by two factors, the limitation of
measuring instrument (systematic error) and the skill of the
experimenter making the measurements (random error).
• Example: A measurement of 5.07 g ± 0.02 g means that
the experimenter is confident that the actual value for the
quantity being measured lies between 5.05 g and 5.09 g.
The uncertainty is the experimenter's best estimate of how
far an experimental quantity might be from the "true
value."
Examples of Uncertainty
Bob weighs himself on the scale. The smallest
division on the scale are 1-pound marks. Bob reads
his weight close to the 142-pound mark. He knows
his weight is between 141.5 pounds and 142.5
pounds. What is Bob’s weight and uncertainty?
Weight = 142 ± 0.5 pounds
In general, the uncertainty in a single measurement
from a single instrument is half the least count of the
instrument.
Significant Figures
Rules on determining how many significant
figures are in a number:
1. Non-zero digits are ALWAYS significant
2. Any zeros between two significant digits
are significant
3. A final zero or trailing zeros in the decimal
portion ONLY are significant
Significant Figures Examples
1. 246.32
2. 100.3
3. 0.678
4. 0.0001
5. 1.0000
6. 700000
1. 5 sig figs
2. 4 sig figs
3. 3 sig figs
4. 1 sig fig
5. 5 sig figs
6. 1 sig fig
More on Significant Figures
Addition/Subtraction – Round to the least number of decimal
places of any number in the problem
Ex: 32.567+135.0+1.4567 = 169.0237
How many sig figs?? = 169.0
Multiply/Divide – Round to the least number of significant
figures of any number in the problem
Ex: 28.367/3.74 = 7.5847593583
How many sig figs?? = 7.58