What’s the Difference between a Sphere and a Ball?
Forgot your math class from 9th grade on spheres and balls? I am not surprised 🙂
But don’t worry, we’ll make up for it today, it’s quite simple.
What is the difference between a sphere and a ball?
A sphere is a surface, an empty object, such as a ping-pong ball or a basketball.
A ball, on the contrary, is a volume, a solid object, like a pétanque ball or a planet.
If you were just looking for the difference between the two you have your answer. For those who want to go further, I suggest you read the rest of the article.
Sphere
Definition
Closed surface where all points are at the same distance (radius) from an inner point (center); solid limited by the previous surface.
Larousse Dictionary
Unlike a ball, there is no point inside the radius.
It’s a 3D circle if you want.
Examples
Here are a few more examples to help you get a better idea of a sphere:
- A soap bubble (if it is perfectly round)
- One tennis ball (except for the grooves)
- The different balls (soccer, basketball, volleyball, …)
- A Christmas ornament (although we still call it a ball, it’s usually empty nowadays)
Calculations
For the most motivated among you, here are the calculation formulas to know about a sphere
Number Pi (π)
The number Pi (π) will come up often in the calculations on this article, so it is important to know what we are talking about.
The number π is a mathematical constant. It is defined as the ratio of a circle’s circumference to its diameter, and it also has various equivalent definitions. It appears in many formulas in all areas of mathematics and physics. As you probably already know, it’s approximately equal to 3.14159.
Perimeter
The sphere’s (or ball’s) perimeter is the same as that of the corresponding circle.
As I told you, a sphere is nothing but a 3D circle, so you can calculate the perimeter with the same formula.
P = 2πr
- P = Perimeter
- π = constant
- r = radius size (distance between the center and the edge of the sphere, half-diameter)
Surface
Let’s get down to business, the previous paragraph was just a reminder 🙂
Here is the formula to calculate the area of a sphere :
A = 4πr²
The area of a sphere, is thus the radius squared multiplied by 4π
Example:
- The Earth has a radius of 6371 km.
- Its surface is therefore 4 * π * (6371×6371)
- This gives us 510 million square kilometers
Ball
Definition
Solid sphere, of any material.
Larousse Dictionary
The definition is short 🙂
But it is not necessary to say more about it.
A ball is nothing more than a sphere filled with substance.
Examples
As for the sphere, here are some examples of balls :
- The planets, the Earth in particular, are filled with matter below the surface.
- The pétanque ball
- Rounded fruits: apple, orange, … An orange has a spherical skin, but is indeed a ball.
- Marbles
- A snowball
Calculations
The calculations are all the same as for the sphere.
The perimeter and surface area are calculated in the same way.
By the way, you have noticed that I took the Earth as an example for the calculation of the sphere’s surface when it is a ball 🙂
The only additional formula we have to see, is the calculation of the volume.
Volume
The volume of a ball is calculated using the following formula:
V = 4/3 π r3
The volume is thus calculated by multiplying the cube of the radius by 4/3 of π.
The result is in cubic centimeters if the radius is in centimeters.
Comparison table
| Sphere | Ball |
|---|---|
| Solid limited to its outer surface | Solid sphere, filled with something. |
| A sphere has a perimeter and a surface only | A ball has also a volume |
Conclusion
There, you now know the difference between a sphere and a ball, and their formulas have no more secrets for you 🙂
It’s easier to say when you have the explanation in front of you, but less obvious when you cross these terms every 10 years ^^
Maybe try to keep an example of each one in mind so that you don’t forget the difference.
