# What Is the Difference Between Major Arcs, Minor Arcs, and Semicircles in Geometry?

Have you ever looked at a circle and wondered what the difference is between a major arc, a minor arc, and a semicircle? These terms can often be confusing, but understanding the differences between them is essential when working with circular shapes, especially in fields like engineering and math.

To start, a major arc is an arc that measures more than 180 degrees and encompasses more than half of the circumference of a circle. On the other hand, a minor arc is an arc that measures less than 180 degrees and encompasses less than half of the circle’s circumference. Finally, a semicircle, as the name suggests, is an arc that measures exactly 180 degrees and divides the circle into two equal parts.

When it comes to understanding the differences between these arcs, it’s important to note that a major arc and a minor arc can share the same endpoints, but their measures and positions on the circle will be different. Meanwhile, a semicircle will always have endpoints that are diametrically opposite to each other.

## Definition of an Arc

An arc is a portion of a circle’s circumference. In other words, when a circle is cut into two or more pieces, each piece is called an arc. The endpoints of the arc are points on the circumference of the circle, and the arc itself is the shortest distance between these endpoints along the circumference.

There are three types of arcs: major arcs, minor arcs, and semicircles. The difference between them lies in the length of the arc and the angle it subtends at the center of the circle. Major arcs are the longest arcs, while minor arcs are the shortest, and semicircles are exactly half of the circumference of the circle.

Type of Arc Angle Subtended at Center Length of Arc
Major Arc Greater than 180° Longest
Minor Arc Less than 180° Shortest
Semicircle 180° Half of circle’s circumference

## Classification of Arcs

Understanding the basic definitions of arcs is important to correctly classify them. There are several types of arcs which are classified based on their position and curvature on the circle. The three main types of arcs are major arcs, minor arcs, and semicircles.

## Classification of Arcs based on Size

• Major Arcs: These are arcs that measure more than 180 degrees but less than 360 degrees, also referred to as an obtuse angle. Major arcs can be found on the outer border of the circle and can be described as the longer length of an arc that spans beyond the diameter of the circle.
• Minor Arcs: These are arcs that measure less than 180 degrees, also known as an acute angle. Minor arcs can be located in the interior of the circle and are shorter in length, spanning less than the diameter of the circle.
• Semicircles: These arcs are exactly half of the circumference of the circle, or 180 degrees in measure. Semicircles are the largest examples of minor arcs and have a diameter as their defining line.

## Classification of Arcs based on Position and Curvature

Arcs can also be classified based on their position and curvature. These classifications include:

• Central Arcs: These are arcs that span from one point on the circumference of the circle to another point, passing through its center.
• Circumferential Arcs: These arcs span the circumference of the circle and do not pass through the center.
• Tangent Arcs: These are arcs that are tangent to the circle, like the tangent line, but extend to curve in one or both directions.

## Classification of Arcs in a Circle

When multiple arcs exist within the same circle, they can be classified further into four categories – overlapping, congruent, adjacent, and opposite. The following table illustrates these classifications:

Arcs Classification Explanation
AB, BC, CD, DA Adjacent Located in the same circle and share only one point.
AC, BD Opposite Located in the same circle and share no common points.
AB, CD Congruent Equally sized and located in the same circle.
AB, AD Overlapping The two arcs share a common point and overlap, but do not share a common length or section.

Knowing the different classifications of arcs enables us to solve geometric problems and can improve our understanding of circular geometry.

## Properties of Major Arcs

Arcs are curved segments of a circle. They can be categorized as major, minor, or semicircles. A major arc is an arc that measures more than 180 degrees. Let’s look at the properties that make major arcs unique:

• A major arc is a subset of the circumference of the circle. Therefore, the length of a major arc is greater than that of a minor arc but less than the circumference of the entire circle.
• The central angle of a major arc is greater than 180 degrees. In other words, the angle formed by the rays that define the arc is an obtuse angle.
• The complement of a major arc is a minor arc. The angles formed by these arcs are complementary angles; they add up to 90 degrees.

Now, let’s take a look at an example to illustrate these properties:

Consider a circle with a diameter of 10 cm. If angle AOB is a central angle that measures 240 degrees, then the arc AB is a major arc. Here’s how we can apply the properties we just learned:

• The length of arc AB is (240/360)*(pi*10) = 16.67 cm.
• The central angle of arc AB is 240 degrees, which is greater than 180 degrees.
• The complement of arc AB is arc CD, which is a minor arc. Angles AOC and BOD are complementary angles that add up to 90 degrees.

## Examples of Major Arcs in Real Life

Major arcs can be found in various shapes and structures in the world around us. From the arches of bridges and doorways to the curves of roller coasters, major arcs can be seen in many forms. Here are a few examples:

• The Gateway Arch in St. Louis, Missouri is a 630-foot tall arch made of stainless steel. Its legs form a major arc that spans 630 feet and is visible from miles away.
• The Sydney Harbour Bridge in Australia is a steel through arch bridge with a span of 503 meters. Its arch forms a major arc that is both functional for transportation and aesthetically pleasing.
• The Superman: Krypton Coaster at Six Flags Fiesta Texas is a roller coaster with a track that forms a major arc. Riders are sent through a series of drops and turns that follow the shape of the arc.

## Conclusion

Major arcs are fascinating curves that can be found all around us. They have distinctive properties that set them apart from minor arcs and semicircles. By understanding these properties, we can identify major arcs in various shapes and structures and appreciate their beauty and form.

Properties of Major Arcs
A major arc is a subset of the circumference of the circle. The length of the arc is greater than that of a minor arc but less than the circumference of the entire circle.
The central angle of a major arc is greater than 180 degrees. The angle formed by the rays that define the arc is an obtuse angle.
The complement of a major arc is a minor arc. The angles formed by these arcs are complementary angles that add up to 90 degrees.

References:

https://www.mathsisfun.com/geometry/circle-arc-length.html

https://www.mathopenref.com/arc.html

https://www.thoughtco.com/major-arc-definition-373408

## Properties of Minor Arcs

Minor arcs are arcs that measure less than 180 degrees in a circle. They are formed by two points on a circle that are not the endpoints of the diameter in the circle. Minor arcs have notable properties that influence how they are measured, identified, and compared:

• Minor arcs are parts of circles that are less than half the length of the circle’s circumference. Therefore, the length of a minor arc is less than πr, where r is the radius of the circle.
• Minor arcs in a circle that have the same central angle are equal in size. Thus, the size of a minor arc can be determined by calculating the central angle of the circle that it subtends.
• Minor arcs in circles that have equal radii and central angles are equal in length. This implies that the length of a minor arc that subtends a particular central angle is a function of the radius of a circle.

Computing the properties of minor arcs involves the use of arc length and central angle measurements. A table of selected minor arc values for some common central angles is provided below:

Central Angle (degrees) Arc Length (radians) Arc Length (r)
30 π/6 rπ/6
45 π/4 rπ/4
60 π/3 rπ/3
90 π/2 rπ/2

The properties of minor arcs are crucial in several disciplines, including mathematics, physics, engineering, and computer science. The ability to measure, estimate, and compare minor arcs provides insights into various calculations, models, and simulations that involve angles and circles.

## Properties of Semicircles

A semicircle is half of a circle and is formed by dividing a circle into two equal parts by drawing a diameter. A semicircle has unique properties that are different from a major or minor arc. Here are some of the properties of semicircles:

• A semicircle has an angle of 180 degrees at its center, which is twice the size of a right angle.
• The length of the diameter of a semicircle is twice the length of the radius of the circle that it came from.
• The circumference of a semicircle is half the circumference of the circle that it came from.

A semicircle is an essential concept in geometry, as it forms the basis for several other shapes, including segments and sectors of circles. It is also an important aspect in the study of trigonometry, especially when dealing with angles and degrees.

When it comes to solving problems involving semicircles, it is essential to have a clear understanding of its properties and how they can be used to determine other characteristics of the shape. For example, finding the area or perimeter of a semicircle often requires knowledge of its diameter or radius, as well as the formula for calculating its area or circumference.

In summary, a semicircle is half of a circle and has unique properties that make it distinct from a major or minor arc. Understanding these properties is essential for solving problems involving semicircles and is an important aspect of geometry and trigonometry.

## Types of circles

A circle is a geometric shape consisting of all points equidistant from a central point called the center. In geometry, there are different types of circles, and each type has unique features that distinguish it from other circles. This article will explore these types of circles and their characteristics, including:

• Major arcs
• Minor arcs
• Semicircles
• Tangent circles
• Concentric circles
• Circumference

## Major Arcs, Minor Arcs, and Semicircles

In a circle, an arc is a part of the circumference between two points. There are two types of arcs: major arcs and minor arcs. A major arc is an arc that measures more than 180 degrees but less than the entire circumference of the circle. On the other hand, a minor arc is an arc that measures less than 180 degrees. A semicircle is a special type of arc that measures exactly 180 degrees, and it divides the circle into two equal parts.

Generally, arcs are named based on the two endpoints that define them. For instance, if AB and CD are the two endpoints of an arc, the arc can be denoted by ABDC or CDAB. It is worth noting that the direction in which the arc is drawn also affects its name. For example, if arc AB is drawn clockwise and arc CD is drawn counterclockwise, they are considered different arcs, and they should be named differently.

A good way to visualize the difference between major arcs, minor arcs, and semicircles is to imagine a clock. If you draw two points on the clock, one at 3 o’clock and the other at 9 o’clock, you can create a minor arc that measures 90 degrees. Similarly, if you draw two points on the clock, one at 3 o’clock and the other at 6 o’clock, you can create a semicircle that measures 180 degrees. Finally, if you draw two points on the clock, one at 3 o’clock and the other at 12 o’clock, you can create a major arc that measures 270 degrees.

Type of Arc Degree Measure Endpoints
Major Arc Between 180 and 360 degrees ABDC or CDAB
Minor Arc Less than 180 degrees AB or BA
Semicircle Exactly 180 degrees AB or BA

Understanding the difference between major arcs, minor arcs, and semicircles is essential in geometry, as it helps students solve problems involving circles. For example, a student might be asked to find the length of an arc or the radius of a circle given the length of an arc and the measure of a central angle. In such a case, knowing the type of arc involved is crucial in coming up with the right approach to the problem.

## The Relationship Between Radius and Arc Length

Understanding the relationship between radius and arc length is crucial when it comes to differentiating between major arcs, minor arcs, and semicircles. The radius of a circle is the distance from the center of the circle to any point on the circumference. The arc length is the distance along the circumference of a part of the circle, between two points on the circumference that are separated by a certain angle. A semicircle is half of a circle, while a major arc is an arc that measures more than 180 degrees and a minor arc is an arc that measures less than 180 degrees.

• When the radius of a circle increases, the arc length also increases. This means that the larger the radius of a circle, the longer the arc length between two points on its circumference.
• If two circles have the same radius, the arc length will be proportional to the measure of the central angle. This means that the arc length will increase as the angle increases.
• Conversely, if two arcs of different circles have the same arc length, the arc on the circle with a larger radius is smaller in terms of angle measurement than the arc on the circle with a smaller radius.

For example, consider two circles, one with a radius of 3 cm and another with a radius of 6 cm. Let’s say we measure an arc length of 4 cm on both circles. The angle of the arc on the circle with a radius of 3 cm will be larger than the angle of the arc on the circle with a radius of 6 cm.

The table below shows the relationship between the radius and arc length for different values of central angle:

30 1.57 cm 3.14 cm
60 3.14 cm 6.28 cm
90 4.71 cm 9.42 cm

Understanding the relationship between radius and arc length is essential for many geometric calculations, especially in fields such as engineering, architecture, and physics. By knowing the radius and the arc length of a circle, one can easily find other properties of the circle, such as its circumference, area, and diameter.

## FAQs: What is the Difference Between Major Arcs, Minor Arcs and Semicircles?

1. What is a major arc?
A major arc is an arc that measures greater than 180 degrees on a circle. It spans more than half the circumference of the circle.

2. What is a minor arc?
A minor arc is an arc that measures less than 180 degrees on a circle. It spans less than half the circumference of the circle.

3. What is a semicircle?
A semicircle is an arc that measures exactly 180 degrees on a circle. It spans exactly half the circumference of the circle.

4. Can a semicircle be considered as a type of arc?
Yes, a semicircle is a type of arc, specifically a circular arc that has a measure of 180 degrees.

5. What is the difference between a major arc and a minor arc?
The main difference between a major arc and a minor arc is their length. A major arc is longer, and it spans more than half the circumference of a circle. A minor arc is shorter, and it spans less than half the circumference of a circle.

## Closing Thoughts

Thanks for reading our FAQs on the difference between major arcs, minor arcs, and semicircles. To summarize, a major arc measures more than 180 degrees, while a minor arc measures less than 180 degrees. A semicircle is a type of arc that measures exactly 180 degrees. Remember to revisit this page if you have any more questions or concerns about geometry.