Ch. 3, Scientific Measurement. Measurement : A quantity that has a and a. Like 52 meters.
CH 2: Scientific Measurement
description
Transcript of CH 2: Scientific Measurement
![Page 1: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/1.jpg)
CH 2: Scientific Measurement
Renee Y. BeckerCHM 1025
Valencia Community College
1
![Page 2: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/2.jpg)
Measurements
• Measurement
– A number with an attached unit
Examples: 15 inches 3 cups 36 cm
Every measurement must include units!!
2
![Page 3: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/3.jpg)
Example 1: Measurements
In the following, what are the measurements and what are the units?
a) 12 trees
b) 2.3 mm
c) 100 ¢
3
![Page 4: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/4.jpg)
Measurements
• Instrument– A device for recording a measurement• Examples: Ruler (length), electronic balance (mass),
Graduated cylinder (volume)
4
![Page 5: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/5.jpg)
Uncertainty
• An instrument may give a very sensitive reading, but EVERY measurement has UNCERTAINTY
• No measurement instrument is perfect and neither is the person using it
5
![Page 6: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/6.jpg)
Example 2: Length Measurements
• If we need to measure the length of this candycane, which ruler should we use? Why?
6
![Page 7: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/7.jpg)
Mass
• Mass– Measure of the amount of matter it possesses– Measured by a balance– Not affected by gravity– Typical units: kilogram (kg), gram (g), pound (lb),
ounce (oz)
• Weight– Force exerted by gravity on an object
7
![Page 8: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/8.jpg)
Balances
8
![Page 9: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/9.jpg)
Example 3: Mass
• Would you have the same mass on the moon as on Earth? Why?
• Would you have the same weight on the moon as on Earth? Why?
9
![Page 10: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/10.jpg)
Volume
• Volume– The amount of space occupied by a solid, gas, or
liquid
– Graduated cylinder, pipet, buret, volumetric flask, syringe
– Typical units: milliliter (mL), Liter (L), centimeter cubed (cm3), quart (qt), gallon (gal),
10
![Page 11: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/11.jpg)
11
![Page 12: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/12.jpg)
Buret
12
![Page 13: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/13.jpg)
Accuracy, Precision, and Significant Figures in Measurement
• Accuracy is how close to the true value a given measurement is.
• Precision is how well a number of independent measurements agree with one another.
13
![Page 14: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/14.jpg)
Accuracy, Precision, and Significant Figures in Measurement
• Significant Figures are the total number of digits in the measurement.
• The results of calculations are only as reliable as the least precise measurement!!
• Rules exist to govern the use of significant figures after the measurements have been made.
14
![Page 15: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/15.jpg)
Accuracy, Precision, and Significant Figures in Measurement
• Rules for Significant Figures:
– Zeros in the middle of a number are significant
– Zeros at the beginning of a number are not significant
– Zeros at the end of a number and following a period are significant
– Zeros at the end of a number and before a period may or may not be significant.
15
![Page 16: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/16.jpg)
Example 4: Significant Figures
How many Sig. Figs ?
a) 0.000459
b) 12.36
c) 36,450
d) 8.005
e) 28.050
16
![Page 17: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/17.jpg)
Accuracy, Precision, and Significant Figures in Measurement
• Rules for Calculating Numbers:
– During multiplication or division, the answer
can’t have more sig figs than any of the original
numbers.
17
![Page 18: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/18.jpg)
Example 5: Significant Figures
a) 238.5 x 79 =
b) 12 / 0.1272 =
c) 0.2895 x 0.29 =
d) 32.567 / 22.98 =
18
![Page 19: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/19.jpg)
-During addition or subtraction, the answer can’t have more digits to the right of the decimal point than any of the original numbers.
Accuracy, Precision, and Significant Figures in Measurement
19
![Page 20: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/20.jpg)
Example 6: Significant Figures
a) 238.5 + 79 =
b) 12.3 - 0.1272 =
c) 0.2895 + 0.29 =
d) 32.567 - 22.98 =
20
![Page 21: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/21.jpg)
Accuracy, Precision, and Significant Figures in Measurement
• Rules for Rounding Numbers:
– If the first digit removed is less than 5 - round down
– If the first digit removed is greater than 5 - round up
– If the first digit removed is 5 and following numbers are nonzero - round up
– If the first digit removed is 5 and following numbers are zero - round down
– Only final answers are rounded off, do not round intermediate calculations
21
![Page 22: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/22.jpg)
Example 7: Rounding
Round off each of the following measurements
(a)3.774499 L to four significant figures
(b) 255.0974 K to three significant figures
(c) 55.265 kg to four significant figures
22
![Page 23: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/23.jpg)
Example 8: Accuracy & Precision
Which of the following is precise but not accurate?
23
![Page 24: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/24.jpg)
Scientific Notation
• Changing numbers into scientific notation– Large # to small #– Moving decimal place to left, positive exponent
123,987 = 1.23987 x 105
– Small # to large #– Moving decimal place to right, negative
exponent0.000239 = 2.39 x 10-4
• Correct scientific notation: #.#### x 10n
24
![Page 25: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/25.jpg)
Scientific Notation
25
How to put into calculator??
![Page 26: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/26.jpg)
Example 9: Scientific Notation
Put into or take out of scientific notation
a) 87542
b) 2.1956 x 10-3
c) 0.784
d) 2.78 x 106
e) 92000
26
![Page 27: CH 2: Scientific Measurement](https://reader035.fdocuments.net/reader035/viewer/2022062410/56815d91550346895dcba997/html5/thumbnails/27.jpg)
Significant Figures
• When we count something, it is an exact number.
– It has an infinte number of significant figures
27