Scientific Measurements and Density

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Scientific Measurements and Density
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• Measurements are an everyday part of science
  class.
• It is very important to be as accurate as
  possible when taking measurements.

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Length

• In science, we use the metric system. So lengths
  are measured in units like millimeters (mm),
  centimeters (cm), meters (m), and kilometers (km).

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Take a look at the meter stick above. On the
bottom, the longest lines represent each whole
centimeter (cm). The medium length lines are each
½ or .5 of a centimeter (cm) or 5 millimeters
(mm). The smallest lines are each 1
millimeter. There are 10 mm in 1 cm and there are
100 cm in 1 meter (m).
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Lets figure out the answers now!
A. 2.3 cm
B. 5.1 cm
C. 10.0 cm
What is the distance between points
A and B 2.8 cm
A and C 7.7 cm
B and C 4.9 cm
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Why is it better to align the meter stick so that
the edge of the object being measured is at the 1
cm mark rather than the end to the meter stick?
Because the meter stick may be worn at the edge
and you will not get an accurate reading.
But be careful!! If you start at the 1 cm mark,
you must allow for that in your final answer by
subtracting 1 cm from your answer.
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Length

• In making a measurement of length, the meter
  stick should be placed on its edge so that the
  scale rests on the object as shown on your paper.
  Can you explain why?
• Being eye-level will make your answer more
  accurate!

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Length

• An enlarged section of a metric ruler is shown
  below. There are letters along the bottom edge
  of the ruler. Write the correct measurement for
  each letter in the space next to the correct
  letter on your paper.

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• A. 20.5 cm
• B. 19.3 cm
• C. 21.25 cm
• D. 21.95 cm
• E. 18.3 cm
• F. 20.0 cm
• G. 17.7 cm
• H. 20.95 cm
• I. 22.3 cm
• J. 19.7 cm

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Temperature

• Temperature is a measure of the average vibration
  of the particles that make up a substance.
• In other words, the faster the particles are
  vibrating, the warmer they are and thus the
  higher the temperature.
• BE CAREFUL! Temperature and heat are NOT the
  same thing!!
• Heat is a type of energy, temperature is a
  measure of that energy.

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Temperature

• The instrument used to measure temperature is a
  thermometer.
• The units of temperature are degrees. There are
  three different degree scales.
• 1. Fahrenheit (F) used in U.S.
• 2. Celsius (C) - metric
• 3. Kelvin (K) used mostly in science, known as
  the SI unit for temperature. The Kelvin scale is
  based on absolute zero.

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Temperature and your ESRT pg. 13
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Time

• In this class, you will be using a stopwatch most
  often to measure time. Its VERY important to
  know how to read one accurately!
• PAY ATTENTION this is not in your notes, just
  watch and learn!

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Stopwatches are generally divided into 4
sections Hours, minutes, seconds, and
milliseconds. In stopwatch A the correct
reading would be 4.06 seconds. In stopwatch B
the correct reading would be 6.59 seconds. What
would be the readings of stopwatch A and B if you
were asked to round to the nearest tenth? (one
place after the decimal)
A 4.1 seconds
B 6.6 seconds
A
B
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Volume

• Volume is how much space an object takes up.
• Both liquids and solids have a volume.

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Volume of Liquids

• The instrument used to measure volume of liquids
  is a graduated cylinder.
• Most of the time, the units used to measure
  volume are milliliters (mL).

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Volume of Liquids
meniscus
37.0
8.6
22.0
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Volume of Rectangular Solids

• The most common instruments for measuring the
  volume of rectangular solids are rulers and/or
  meter sticks.
• The formula for volume of a rectangular solid is
  V L x W x H.
• Units are cubic units because there are three
  sides being multiplied by each other.
• cu. cm or cm³
• cu. m. or m³
• 1 cubic centimeter 1 milliliter

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Lets try it now! determine the volume of each
illustration on your paper.
V L x W x H V (3cm)(3cm)(3cm) V 27.0 cm³
V L x W x H V (8m)(6m)(3m) V 144.0 m³
V L x W x H V (4cm)(4cm)(10cm) V 160.0 cm³
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Volume by displacement used for solids that are
irregularly shaped.
20.0 mL
25.0 mL
5.0 mL (25 mL 20 mL)
meniscus
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Mass

• Mass - how much matter or stuff is in an
  object.
• Traditionally, the instrument used to measure
  mass is a triple beam balance. However, in these
  modern times, we now use an electronic balance.
• The 2 units most commonly used to measure mass
  are grams (g) and kilograms (kg).

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This
year you will be using an electronic balance like
below. Basically, turn balance on, press the
zero button, place object on the scale and it
will automatically give you a reading!

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Weight

• Weight is the amount of gravitational force
  acting on an object.
• Mass and weight are NOT the same thing!!! Weight
  is a FORCE, Mass is the stuff in an object.
• The instrument used to measure weight is a spring
  scale.
• The metric units of weight are Newtons (N). The
  English units of weight are pounds (lb).

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Weight

• There are 2 factors that affect weight
• 1. The amount of mass the object possesses.
• 2. The amount of gravity acting on the object.

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Weight
Another object, which is smaller, has less mass
and so it weighs less.
Using a spring scale, the weight of this ruler
can be measured.
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Weight
The ruler, here on Earth, has a certain weight.
However, on the moon, it weights much less due to
less gravity pushing down on the ruler.
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Density

• Density is the amount of matter (stuff) that
  occupies a given space.
• In other words, it has to do with BOTH mass and
  volume.
• If an object has the same stuff in it, but gets
  bigger it will be less dense.
• If an object stays the same size, but has more
  stuff in it, it will be more dense.

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Density
Least Dense
Most dense
Above, all three objects are the same size, but
the one on the left has much less stuff in it
than the one in the middle or the one on the
right, so it is least dense. The one on the
right has the most stuff (mass) inside its
given volume, so it is most dense.
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Density

• The formula for density is D Mass/Volume
• The formula is found on page 1 of your ESRT.
• Using the density triangle, you can easily figure
  out the formulas for mass and volume as well.

M
D
V
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Density

• Instruments
• For density of liquids, you would use a graduated
  cylinder to get the volume and then an electronic
  balance for the mass.
• For density of solids, you would use a ruler and
  VL x W x H to get the volume and an electronic
  balance for the mass.

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Density

• Units
• It depends on what the object is and the units of
  mass and volume that were used. The two most
  common are
• 1. g/mL
• 2. g/cm³
• Notice that there are always TWO units in density
  because you are multiplying mass and volume and
  neither of those cancel each other out.

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Putting it all together now!
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Solving Density Problems
Density M / V
D 150 g /
10 cm³
D 15 g/cm³
V L x W x H
V (5cm)(1cm)(2cm)
V 10 cm³
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Solving Density Problems
D M / V
D 125 g /
50 mL
D 2.5 g / mL
300
250
Object X
300 mL 250 mL 50 mL
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What if you already know the density of an object
and asked to solve for mass or volume??

• Use the density triangle!
• Example The density of an object is 5.5 g/mL and
  the volume is 8 mL. What is the mass?
• 44.0 g

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Density Relationships

• There are several factors that may affect an
  objects density.
• We will discuss four
• Size
• Temperature
• State of Matter
• Pressure

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Density vs. Size

• SIZE DOES NOT MATTER!!
• Relationship as long as the substance stays the
  same, the density will NOT change.
• Ex.) lead has the same density no matter if its
  a huge piece or a very small piece.

Density
Size
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Density vs. Temperature

• When an object heats up, the volume will
  increase, due to the object getting larger. The
  mass will stay the same and thus the density will
  decrease.

Inverse or indirect relationship
density
Temp.
Therefore, the relationship is as temperature
increases density will decrease.
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Density vs. State of Matter
solid
liquid
gas
least
most
density
Solid objects have a lot of stuff packed
tightly together so, they are most dense. The
particles in gases have a lot of room to move!

• The water rule the ONLY exception to this is
  that water is MOST dense in its LIQUID state at
  4C

Water ONLY
Regular
Density
Density
S
L
G
S
L
G
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Density vs. Pressure
As more pressure is exerted on a gas, the volume
will decrease, due to a smaller area for the
particles to move. Now they are packed tightly
together. The mass stays the same and therefore,
the density will increase.
Thus, the relationship is as pressure increases,
density will also increase.
Density
Direct Relationship
Pressure