Measurements, quantities, and important numbers of physics in full

Measurements, quantities, and important numbers of physics in full

You must have done a measurement. For example measuring the length of a table with a bar or often called a meter. You can see other measuring activities, for example, measuring the mass of rice, the mass of meat and measuring the length of a plot of land. Do you understand what actually measures it? What are the benefits of measuring? And how? You can answer this question by studying this chapter. Therefore, after learning this chapter you are expected to be able to:
1. do data retrieval and understand important numbers,
2. processing measurement data,
3. using a length, mass and time measuring device in data retrieval,
4. distinguish the principal quantity and derivative quantity,
5. determine the unit and dimensions of a quantity,
6. use dimensions in physical analysis

A. Introduction

In learning your physics you will always be connected with measurements, quantities and units. Do you know what is called measurement, quantity and unit? It is in this first chapter of physics that you can learn a lot about these meanings and must be able to use them in every physical study.
Measurement is a measuring process. While the measure is defined as an activity to compare a quantity with a standard amount that has been determined in advance. From this understanding, it can be derived from the next understanding, namely quantity and unit. Magnitude is defined as everything obtained from the measurement results expressed in the form of numbers and units.
From the explanation above, it can be seen that measurements, quantities and units have a close relationship. All three are always related. Measurement is an activity or activity, magnitude is the subject matter that is measured while the unit is a comparison (the measure). For example, Anita measures the length of her pants. The amount measured is the length and unit used for example meters.
In the field of physics and its application there are many quantities and units known. For example, the length of the unit is meter, the mass of the unit is kg, the weight of the unit is new, the unit is m / s and the current is strong. Learn more about these measurements, quantities and units in the following sections

B. Measurement

In front of you you have explained what is meant by measurement. In learning physics, it cannot be separated from measurement. There are three important things related to measurement, namely: data collection, data processing and use of measuring instruments. You can look at these three things in the following explanation.

1. Taking Data and Important Numbers

Have you ever done data collection activities? The measurement process to obtain the measurement data is called data retrieval. Can the measurement results get the right value? Many measurement processes occur errors. Errors can occur from people who measure, measure or environment. To load all the conditions, the measurement results are known to have a fixed number and estimated number. The combination of the two numbers is called an important number.
An important number is a number obtained from the measurement results consisting of exact numbers and estimated numbers. The value of each measurement result is an important number. Such information above the important number consists of two parts. First, the exact number is the number shown on the scale of the measuring instrument with the existing value. The two estimated numbers are the number of measurement results obtained by estimating the value. This value arises because what is measured lies between the smallest scale of the measuring instrument. In each measurement it is only permissible to give one estimate. To understand this important number you can look at the following example.

EXAMPLE

A group of students who measure object mass using a spring balance tool. In the measurement, it appears that the scale is shown in Figure. Aghnia writes the results of 8.85 gr while John writes the results of 8.9 gr. Which results are correct?
Solution: Try to look at the picture. From the picture it can be obtained: The exact number = 8 gr Estimated number = 0.9 gr (can only be one estimate, may not be 0.85 because of 2 estimated numbers) The measurement result is m = exact number + estimated number = 8 + 0, 8 = 8.8 gr So what is more permanent is the result John. To better understand this example you can try the following question. A pencil is measured in length with a ruler centimeter.

To get the right measurement results, mistakes can be avoided. These steps include the following.

a. Choose a more sensitive device

 The first step to taking measurements is to choose a tool. A measuring device can vary in size. For example a mass measuring device. Of course you already know there are scales (for rice or the like), spring balance, O’hauss balance sheet (in the laboratory) and there are more analytical balance sheets (can be used to weigh gold). All these devices have the smallest sensitivity or scale that is different. To get more precise results: first, choose a tool that is more sensitive (more thorough). For example analytical balance has a high accuracy of up to 1 mg. Second, choose a tool that is suitable for use (eg balance sheet analysis to measure small objects such as gold masses).

 b. Perform calibration before use

Perform calibration before use Calibration is commonly used on meteorological and geographic bodies. For example, for scales that have been used for a long time, calibration needs to be done. Calibration is the return of values ​​to the measuring instrument. The calibration process can also be carried out in a small scope, namely the collection of experimental data in the laboratory. Very often the measuring instrument used has an initial state that is not zero. For example, a spring balance when it has not been given a load, the needle has shown a certain value (not zero). The state of a tool like this that needs calibration. Usually in the tool there are already parts that can make zero (normal).

c. Make observations with the right position

The environment in which measurements can affect the reading results. For example, the amount of light entering. Use enough light for measurement. After the environment supports it, to read the measurement scale needs the right position. The correct reading position is in the straight direction.

2. Data Processing

Measurement in physics aims to obtain data. What are the benefits of the data obtained? Of course you already know that from these data you can learn the nature of the magnitude being measured. From the data, the next event can be predicted.
From the explanation above, it can be seen how important the measurement data results are. But you need to know that to fulfill the utilization of existing data, it needs to be analyzed or processed. Data processing methods are very dependent on the measurement objectives (experiments) carried out. For example, for class X SMA, three methods of data analysis can be introduced as follows.

a. Generalization method

Measurements or broader experiments at the high school level are aimed at understanding existing concepts. For example, studying the properties of density of water. To find out the nature of the measurement can be carried out then the data is processed. Processing data for this purpose does not need to be complicated, enough from the existing data made general accepted conclusions. One method to make conclusions of problems like this is the method of generalization

c. Statistical calculation method

In physics learning there are many similarities found, there are even students who say, physics is a formula. Are you including those students? Certainly not because you already know that physics not only learns formulas but also other concepts about nature. Physical formulas are a short form of a concept, law or physical theory. One of the uses of the formula is for the calculation and measurement of a quantity. There are physical quantities that can be measured directly by measuring instruments but some are not directly measurable. This magnitude that does not have a measuring instrument can be measured by other quantities that have a relationship in a physical formulation. Examples of measuring the density of objects. This magnitude can be measured by measuring the mass and volume of the object, then the density is calculated by
formula: ρ = m / v. Do measurements that are only done once can get accurate data? The answer is certainly no. You already know that there are many errors in the measurement. To minimize errors, repeated measurements can be made. The value of the measured quantity can be determined from the average value. This calculation is called a statistical calculation. This method can be helped by a table as in table. Even in this analysis the absolute error (standard deviation) can be calculated from the measurement.