Chapter: Measurement

Transcription

1 Table of Contents Chapter: Measurement Section 1: Description and Measurement Section 2: SI Units

2 *Section 1 Description and Measurements

3 Measurement Measurement is a way to describe the world with numbers. What sort of measurements do you do in real life? Weight, quantities,costs, distances, periods of time.

4 Important: *Measurements of a single item might vary depending on the measuring device you are using.

5 Measurement *In science, it is important to execute your measurements very carefully so you can trust the information *Good part of the data you collect in experiments are the result of measurements

6 Description and Measurement Estimation Estimation- it is a rough measurement It is a skill based on previous knowledge For example, doorknobs are about 1 m above the floor

7 Figure 3 - page 44 See page 44 of the text book, figure 3 Read and think about your answer. When do we use estimation? When we don t need to know the exact measurement.

8 Sometimes we need to know the exact value: Then we will perform a measurement USING TOOLS How do we know if our measurement was properly done? Precision and accuracy book pg 46

9 *Precision x Accuracy Accuracy - compares a measurement to its true value If the measurement is close to the actual value this measurement is accurate

10 *Precision x Accuracy Precision - you are precise when you measure something several times and obtain always the same value, or very close.

11 Precision and Accuracy Your house is 3 Km far from your school. Suppose you measure the distance between your home and your school five times and obtain five measurements equal to 2.5 km. Are you being precise or accurate? Precise

12 Precision and Accuracy Your house is 3 Km far from your school. Suppose you measure the distance between your home and your school five times and obtain five measurements equal to 3 km. Are you being precise or accurate? Both!!!!!!!!!!!!!!!!!!!

13 Section 2 SI Units SI stands for International System of Units

14 IMPORTANT: Communication is very important in science. How do scientists in different countries with different measurement systems communicate and compare their experiment results???

15 In 1960: scientists decided to use an agreed-upon standard of measurement known as International System of Units (SI) ( also called Metric System) Why is it better?????

16 Advantages of using a common system of measurement in Science Facilitates the exchange, understanding and comparison of scientific data

17 Advantages of using the metric System It is and easier system. The SI units are related by multiples of ten, so they are easier to use.

18 The SI units are related by multiples of ten, so they are easier to use.

19 SI Units Prefixes used in measurements Not all are used on our daily lives. More frequently used are: Kilo, centi, milli, micro, nano + the word meter Or liter Or gram

20 SI Units frequently used Length - Kilometer, meter, centimeter Mass - Kilogram, gram, milligram Volume liter, millimeter

21 Conversion factors 1) A conversion factor are used to convert one unit into another. 2) In the metric system any value can be converted into a smaller or larger number by multiplying or dividing by a power of 10.

22 Most used units and conversions - length 1Kilometer (Km) equals 1000 meter (m) 1meter (m) equals 100 centimeters (cm) Conversion: m to km divide by 1000 Km to m multiply by 1000 cm to m divide by 100 m to cm multiply by 100

23 Most used units and conversions - volume 1 liter (l) equals 1000 milliliter (ml) Conversion: ml to l divide by 1000 l to ml multiply by 1000

24 Most used units and conversions - mass 1 Kilogram (kg) equals 1000 grams (g) Conversion: g to Kg divide by 1000 Kg to g multiply by 1000

25 Mass ( kilogram or grams) Kilogram Gram Distance ( Km, m, cm) 1 kilometer Equals 1000 meters 1 meter Equals 10 decimeters and 100 centimeters, 1000 millimeter 1 decimeter Equals 10 centimeter 1 centimeter Equals 10 millimeters Millimeter Volume ( liter and milliliter) 1 liter 1000 milliliter Milliliter Equals 1000 grams Equals 1000 milligrams Milligram Equals 1/1000 1/1000 liter

26 SI Units Length Length is defined as the distance between two points. The meter (m) is the SI unit of length. One meter is about the length of a baseball bat.

27 2 Length SI Units Smaller objects can be measured in centimeters (cm) or millimeters (mm). A pencil would be measured in cm. Long distances from one city to another would be measured in Km.

28 SI Units When using a ruler, make sure to start from 0

29 SI Units Volume The amount of space an object occupies is its volume. The cubic meter (m 3 ) is the SI unit of volume.

30 SI Units Volume To find the volume of a regular object, such as a brick or your textbook, measure its length, width, and height and multiply them together.

31 Volume = length x width x height

32 SI Units *Volume of liquids *For this type of measurement, the tool you use is a graduated cylinder. It is important to read the base of the meniscus.

33 SI Units Volume by Immersion or Displacement Some objects have an irregular shape. When you measure the volume of an irregular object, you start with a known volume of water and drop in, or immerse, the object. The increase in the volume of water is equal to the volume of the object.

34 Volume by Immersion or Displacement for Irregular Solids What is the volume of the stone????

35 SI Units Mass The mass of an object measures the amount of matter in the object. The kilogram (kg) is the SI unit for mass. You can determine mass with a balance.

36 Digital scale

37 SI Units Weight Weight and mass are not the same. Mass depends only on the amount of matter in an object. Weight is the amount of gravity exerted on an object Gravity??????????

38 SI Units Weight (do not put on table) **Gravity is a force that attracts all objects to each other. Bigger objects will attract smaller objects. The SI unit for weight is the Newton (N).

39 Weight In the moon: your weight would change but your mass is the same There is very little gravity on the moon, that is why we have very little weight on the moon and that is why we float on the Moon.

40 Weight On the Moon, the mass of your body ( the amount of matter) is the same as it is on earth Your mass is the same everywhere you go.

41 Spring Scale to measure weight in Newton

42 SI Units Temperature The physical property of temperature is related to how hot or cold an object is. To measure temperature we use thermometers. Temperature is measured in SI with the Kelvin (K) scale or Celsius ( also called Centigrade). The most common is Celsius.

43 2 SI Units Temperature Scales The Fahrenheit and Celsius scales are two common scales used on thermometers and in classroom laboratories.

44 Conversion factors Examples: To convert from Celsius to Fahrenheit and vice-versa F = (C X 1.8) + 32 C = (F 32) X 0.55

45 2 Time Time is the interval between two events. The SI unit of time is the second (s). Time also is measured in hours or minutes.