, 14 March 2013
Pizzas come in a range of sizes. If you’ve ever wondered whether to get one big or two small pizzas, this experiment might be able to help!
Safety: When dealing with food, use clean hands and clean equipment!
Finding the area of a rectangle is a lot easier than most other shapes. All you need to do is multiply the length and the width. By cutting the pizza and rearranging it, you change it from being circular to being (almost) a rectangle. When you cut something up and rearrange the bits, you’ll end up with the same area at the beginning and end. So, measuring the area of a circle becomes as easy as measuring the area of a rectangle.
The rectangle that you made was not completely rectangular. The sides are made of crust, and the crust is curved. However, if you keep cutting the pizza and rearranging it, it will get closer and closer to a rectangle. If you could keep cutting and rearranging forever, then the pizza would make a perfect rectangle.
This idea of breaking something down into bits and rearranging them is very important in mathematics, and not just in geometry.
One nice thing about this activity is that once you’ve seen how it works, you don’t have to cut up every circle to measure the area. All you have to remember is that every circle can be turned into a rectangle in this way.
The short side of your rectangle is going to be the distance along one side of a piece of pizza. This distance is the same as the distance from the centre of your pizza to the edge.
The long side is made up of segments of crust. All of the crust runs along the two long edges, and the whole of those long edges are made from crust, so the length of the long sides is equal to half the length of the crust.
So the area of a pizza is the length of the crust (circumference) divided by two times the distance from the edge to the middle (radius). Mathematicians use a special number called pi to calculate the circumference of a circle. The circumference is two times pi times the radius (2πr). This means the area of a circle is pi times the radius, times the radius. This is more commonly written as pi r squared (πr2).If you’re after more science activities for kids, subscribe to Double Helix magazine!
29 November, 2019 at 7:01 pm
Algebra joke:
Q. What is the volume of a pizza where the radius = z and height = a?
A. Pi•z•z•a
25 June, 2021 at 4:39 pm
I don’t get it