A protractor is used to measure angles.
We conditionally select two parts in the protractor - the “ruler”, also called the rectilinear scale (the lower part in the figure), and the semicircle, also called the goniometric scale. On the semicircle are degrees marks from 0 ° to 180 °. We call the division into degrees “degree grid”.
Protractors come in many forms, but their use is as follows. The protractor has a center mark. In the picture above, this is a small circle with a hole in the center. However, the center mark can be indicated simply by a dash. This label must be aligned with the top of the corner. In this case, one of the sides of the corner should go through the mark with the number 0 on the semicircle of the protractor.
There can be two “zero” marks on the protractor: right and left. It is clear that you should look at the one through which the side of the corner passes. But the most important thing is to understand which degree grid to look at when measuring the angle: upper or lower. If the side of the corner passed through 0, which are located on the outside, then in the future we use the external degree grid. If the side of the corner passed through the “internal” 0, then in the future we use the internal degree grid of the protractor (we do not pay attention to the external).
So, one side of the corner should go through the mark 0, and the second side of the corner should be on the side of the semicircle (goniometric scale), that is, as if to cross it.
At the place where the second side of the angle intersects the goniometer scale of the protractor, the angle is determined.
What does a protractor look like?
The main and required parts of the protractor are two key elements. The first of them is a ruler divided into centimeter divisions. Moreover, such a ruler is usually equipped with a reference point, which is used in the measurement process. The second element of the protractor is a goniometric scale, which is a semicircle, usually including divisions from 0 to 180 °. At the same time, there are modified transport models that have a full dial, that is, they allow you to measure angles from 0 to 360 ° degrees.
Each goniometric scale contains a line of values of the magnitude of the angles in both forward and reverse directions. This allows you to use the protractor to measure both sharp and obtuse angles.
The materials used for the manufacture of transport, can be very different. The most common options for such materials are plastic and metal. Wood is currently less commonly used for these purposes, since such protractors are usually thicker and somewhat less convenient to use.
The measurement accuracy of each tool is directly dependent on its size. So, larger protractors allow you to measure angles with greater accuracy, and small tools give only an approximate idea of the magnitude of the measured angle.
How to use a protractor
Using a protractor, you can solve two main problems: measuring angles and building angles. So, to measure the angle, it is necessary to place its vertex at the reference point indicated on the protractor's ruler. Then you need to pay attention to the side of the corner, directed to the goniometric scale, intersect it. If the length of this side is insufficient, it should be extended to the intersection of the goniometric scale.
After that, you need to look at what value the side of the angle intersects the specified scale. If an acute angle is measured, the desired value will be less than 90 °, and when measuring an obtuse angle, use the part of the scale that contains divisions exceeding 90 °.
Similarly, the construction of angles using a protractor. First you should draw a line that will be one of the sides, and its end, which will become the top, put at the starting point. Then, on a goniometric scale, a point should be noted on the desired angle, which can be either sharp or blunt. After that, removing the protractor, connect the top of the future corner with the dotted point: as a result, you will get the desired angle.
What is a protractor?
A protractor is an object with the help of which each of us can not only measure angles, but also build them. Outwardly, it resembles a semicircular ruler with a scale and divisions. At the bottom, on a flat surface, we’ll find the usual straight ruler for measuring segments. In the upper part there is a semicircle with a double scale for measurements. In each of the directions, the scale is dispersed along the transporter from 0 to 180 degrees.
The school explains what a protractor is in math classes. It is here that there is a need for measurements.
In order for us to know what one degree is, we need to divide the circle into 360 equal parts. One of these parts will be equal to 1 degree. The size of the circle does not affect the degree! This is easy to verify.
Draw two circles of different diameters and divide each into 360 equal parts. Then we impose a smaller circle on a large one and see that the lines coincide.
Measure the angle
A protractor helps build and measure the angle. Degree is a common unit used to measure angles. There are several varieties of angles:
- Acute. This is called an angle of up to 90 degrees.
- A straight angle is 90 degrees.
- The obtuse angle ranges from 90 to 180 degrees.
- The expanded angle is a straight line or 180 degrees.
- The full angle looks like a circle and is 360 degrees.
It’s easy to figure out how to measure the angle. In order to find out what the angle is, we need to set the protractor so that its center is located at the top of the corner, and the straight side coincides with one of its sides. The scale will show us the number of degrees of a given angle. In such a simple way, we can find out what kind of corner is in front of us.
To build an angle with a given degree, you should attach the straight part of the protractor to the line, and its center - to the beginning of the line. Subsequently, this point will be the top of the corner. Then on the scale we look for a given number and put a point. Now the protractor can be removed and connected by a segment to the beginning of the line (the top of the corner) with the marked point.
School stationery produced by different companies differ in material, color, size. So: for those whose protractor turned out to be longer than the length of the corner, and it is not possible to determine its value, the side of the corner must be extended using a straight ruler.
For good reason, junior students are not familiar with the protractor. When applying it, a certain knowledge base should be laid. To fully work with him in the lesson, children study a number of related subjects. Before learning what a protractor is, schoolchildren must perfectly master the straight ruler, draw straight lines, study addition and subtraction, master the compass, know the geometric shapes, and so on. This whole process takes time, and only after graduating from elementary school, the student can add a protractor to his toolbox.
Students are now offered school supplies in a huge selection. Protractor is no exception. Manufacturers are trying to cater to the most demanding customer needs. Tools are made in various colors. Bright colors are always liked by children. Sometimes even in the same class one cannot find the same transportation, which makes it easier to find them when they are lost. Everyone chooses shapes and sizes to their taste.
Most of these products are made of plastic, and this significantly reduces its cost. But there are wooden and even iron protractors. As practice shows, metal, although opaque, is more practical in that the scale is not erased, and this allows you to use it much longer in action, accurately determining the angles.
The protractor is not as demanded by schoolchildren as the ruler, but it accompanies students until the final exam. Some of the graduates of the school choose specialties that are related to measuring and constructing angles, designing buildings and structures, working with drawings. By virtue of their professions, they constantly have to deal with protractors and its derivatives. But the former classmates of current engineers, sometimes even with the deepest humanitarian bias, easily remember the skills of handling this subject and determine the number of degrees at any angle.
Today, modern children are used to extracting any information from the Internet. However, it does not help in measuring angles. Only the ability to use the protractor will make it possible to correctly determine them. This will undoubtedly be useful for future engineers and designers in work, and every educated person should have the skills to work with protractors, so everyone should be able to use such a tool!