# Arc – Definition with Examples

Updated on January 13, 2024

Welcome to another adventure with us at Brighterly, where we light up your child’s learning journey with the spark of knowledge! Today, we’re going to explore a wonderful concept in the world of geometry – the Arc. Just as every great adventure begins with a single step, every circle starts with an arc. If you’ve ever drawn a circle and stopped halfway, you’ve drawn an arc. As simple as it may seem, the arc is a foundational idea in geometry, with numerous practical applications in the world around us. By the end of this exploration, you and your child will have a complete understanding of what an arc is, its characteristics, and how to work with it in mathematical calculations. So, buckle up, and let’s delve into the exciting world of arcs!

## What is Arc in Math?

Picture a circle. You got it? Now imagine cutting out a slice of it like a piece of a delicious pie. That slice, or the curve along the edge of your circle “piece,” is what we call an Arc.

In mathematical terms, an arc is a portion of the circumference of a circle. It’s like a bridge connecting two points on the circle’s boundary. This might seem simple, but the concept of an arc is used in many complex calculations, which we will explore.

## Arc Length Formula

The Arc Length Formula is a tool that helps us figure out how “long” an arc is. In other words, it tells us the distance along the curve of the arc. In simple terms, if you were to walk along the path of the arc, the arc length is the distance you would travel.

The formula to calculate the arc length (L) is:

L = θr

where:

- θ is the central angle (in degrees)
- r is the radius of the circle

## Arc Length Formula in Radians

Hold up! We’ve got another way to measure the central angle, and it’s called Radians. When the angle is measured in radians, the formula to calculate the arc length (L) becomes:

L = θr

where:

- θ is the central angle (in radians)
- r is the radius of the circle

See? The formula stays the same. The only thing that changes is how we measure the angle. Don’t worry; we’ll get into more details about degrees and radians later on.

## How to Find Arc Length of a Curve?

Finding the arc length of a curve might seem like a daunting task. But don’t worry, it’s not that difficult! The arc length of a curve in a plane from a point A(x1, y1) to a point B(x2, y2) can be calculated using calculus and is often denoted as S. The formula for arc length of a curve is:

S = ∫√[1 + (dy/dx)²] dx from x1 to x2

Remember, this formula requires some understanding of calculus, so make sure to study that first!

## How to Find Arc Length With the Radius and Central Angle?

To find the arc length with the radius and the central angle, you use the formula L = θr, as we mentioned before. You need to be cautious about whether your angle θ is in degrees or radians, as this will affect your calculations.

## How to Find Arc Length Without the Radius?

If we want to find the arc length but don’t know the radius, we need to use other information. For example, if we know the diameter (d), we can divide it by 2 to get the radius (r = d/2), then plug this into our formula. In some cases, we might need to use trigonometry to solve the problem.

## How to Find Arc Length Without the Central Angle?

Finding the arc length without the central angle requires some geometry and trigonometry. If you know the radius and the length of the chord, you can use the Pythagorean theorem to find the central angle. Once you have the angle, you can use the arc length formula L = θr.

## Arc of a Circle

The Arc of a Circle is just the term used to refer to any arc that is a part of a circle. It could be a small part of the edge or half the circle or even the entire circle itself!

## Symbol of Arc

The symbol of arc in geometry is a small arc drawn over two points which indicate the ends of the arc. This symbol (∩) is used in geometry to represent an arc.

## Measures of an Arc

There are two main Measures of an Arc:

- The length of the arc (which we’ve been discussing all along).
- The measure of the arc’s central angle.

Both of these measures can be important depending on what we’re trying to calculate.

## Angle of the arc

The Angle of the Arc is simply the angle that is formed at the center of the circle by the two radii that connect to the endpoints of the arc.

## Arc Length Formula

We have mentioned the Arc Length Formula earlier, but just to reiterate, the formula is L = θr, where θ is the angle (in degrees or radians) and r is the radius.

## When the angle is in radians

As mentioned before, when the angle is in radians, the arc length formula doesn’t change. It’s still L = θr. The only thing that changes is how we measure the angle.

## Solved Examples on Arc Length

Let’s dive into some Solved Examples on Arc Length:

- If we have a circle with a radius of 5 cm and the central angle of 60 degrees, the arc length would be: L = θr = (60/360) * 2π * 5 = π/3 cm.
- If the central angle is 1 radian and the radius is 2 cm, the arc length would be: L = θr = 1 * 2 = 2 cm.

## Practice Problems on Arc Length

It’s time to put your knowledge into practice with some Practice Problems on Arc Length:

- Find the arc length of a circle with a radius of 3 cm and a central angle of 90 degrees.
- Find the arc length of a circle with a radius of 7 cm and a central angle of 2 radians.

Remember, practice makes perfect!

## Conclusion

What an incredible journey we’ve been on together! We hope this comprehensive guide has helped to illuminate the concept of arcs for you and your child. Here at Brighterly, we believe that understanding complex ideas starts with grasping the basic concepts, and we’re confident that we’ve achieved that today with our deep dive into arcs. The knowledge of what an arc is, how to measure its length, and how to work with it in mathematical calculations will set the stage for your child to comprehend more advanced topics in geometry. As they continue to explore the amazing world of math, remember that each new concept is like an arc in their growing circle of understanding. Keep practicing, keep asking questions, and keep discovering, because every bright idea brings your child one step closer to their next great discovery!

## Frequently Asked Questions on Arc Length

### Can the arc length be greater than the circumference of the circle?

No, the arc length can never be greater than the circumference of the circle. The longest possible arc of a circle is the circumference itself, which happens when the arc spans the entire circle.

### How is the arc length formula derived?

The arc length formula is derived from the proportion between the angle subtended by the arc at the center of the circle and the total angle at the center of the circle, which is 360 degrees or 2π radians. So, if the angle subtended by the arc is θ degrees or radians, the length of the arc (L) is a fraction of the total circumference, given by L = θ/360 * 2πr (in degrees) or L = θr (in radians).

### What is the difference between arc length and chord length?

The arc length and chord length are both distances, but they measure different things. The arc length is the distance along the curve of the arc from one endpoint to the other, while the chord length is the straight-line distance between the two endpoints of the arc. For a given arc, the arc length is always equal to or greater than the chord length.