Pi Day takes place on March 14th this year, as it has every year since 1988 when this mathematical holiday was invented. Pi Day? Does that sound crazy? Sure it does. It’s irrational. Pi is the world’s most famous “irrational” number. Therefore, Pi Day is the world’s most irrational holiday! Take a circle, any circle, and divide the circumference by the diameter. The quotient is the number called pi, represented by the Greek letter π. It is a little more than three. How much more? That is a question that people have been working on for centuries. Pi is an incredibly useful number in mathematics, physics and engineering. It helps us understand things from the shape of an apple to the energy of stars. It helps us design things, from buildings to spaceships. Pi is an irrational number. That means when you write it as a decimal, its digits do not just end (like 3.5) and they do not repeat in a pattern (like 0.3333…, where the 3s go on forever). Here is a slice of pi: 3.141592653… The “dotdotdot” means the digits keep on going. How far? Is there a pattern? With supercomputers, mathematicians have probed the mysteries of pi to over a trillion digits. The digits keep going. Infinitely. No pattern has ever been found. (Written in an ordinary font, a trillion digits of pi would go around the world 50 times.) But the endless, patternless nature of pi enchants many minds and some people delight in memorizing the digits. A 69 yearold man named Akira Haraguchi recited 100,000 digits from memory in Tokyo in 2006. He shattered the previous record of Chao Lu from China, who had memorized merely 67,890 digits of pi after studying for four years. Can you see a date in the first three digits: 3.14? It’s March 14th — Pi Day! This holiday is celebrated worldwide by students, teachers and math enthusiasts who enjoy pithemed activities, clothing, jokes and food (namely pie). This is an ordinary year as far as Pi Day is concerned, but in 2015, Pi Day was really special. After 3.14, the next two digits of pi are 15. So March 14, 2015, was not just any old Pi Day. It was the “Pi Day of the Century.” You’ll have to wait until March 14, 2115, for another Pi Day so sweet! Happy Pi Day, everybody! David Schwartz probes many mathematical mysteries in his books and school presentations given all over the world. He wrote this Nonfiction Minute while celebrating Pi Day at Tashkent International School in Uzbekistan. He is a member of iNK's Authors on Call and is available for classroom programs through Field Trip Zoom, a terrific technology that requires only a computer, wifi, and a webcam. Click here to find out more. MLA 8 Citation
Schwartz, David M. "Happy Pi Day." Nonfiction Minute, iNK Think Tank, 14 Mar. 2018, www.nonfictionminute.org/thenonfictionminute/HappyPiDay.
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You can’t play tennis unless you know where the ball will be after it bounces. You can’t pass a basketball unless you understand how to angle a bounce so that it goes where you want it to go. As long as the court surface is smooth and flat, a ball’s bounce is very predictable. Its path depends on gravity and on the strength and direction of the force that sets the ball in motion. Thanks to high speed photography we can get a closer look at a bouncing ball. This is a multiple exposure photograph of a bouncing ball. It was taken in complete darkness with the camera shutter open while a highspeed flashing light, called a stroboscope or strobe, flashed 30 times a second. Each flash produced an image. Here’s what you can learn from this photo: The ball is moving fastest where the images are farthest apart and slowest where they are closest together. When the ball is falling, it speeds up. After it bounces and moves opposite the pull of gravity, it slows down at exactly the same rate as it sped up when it was falling until it stops for an instant and starts falling again. Each time it collides with the ground, some energy is lost. That’s why each bounce loses altitude. If the bounce were perfect, no energy would be lost, every bounce would be as high as the last and the ball would bounce forever. A strobe also captures the split second when a tennis ball is struck by a racket. The collision flattens the ball, and stretches the strings and distorts the frame of the racket, all in .005 seconds. If these objects kept their distorted shapes, most of the force of the collision would be absorbed. But they are elastic—they restore themselves to their original shapes after they collide. This restoring force is transferred to the ball to change its direction and help add to the speed of the athlete’s swing. The fastest serve leaves a racket at 130 miles an hour. In a rally, a ballracket collision changes direction of the ball so it is not as fast as a serve, maybe 70 miles per hour. Since the distance between images made by a strobe tells how fast an object is moving, strobes are part of the instruments used to measure the speed of balls from a tennis racket and a baseball pitcher. In this MIT YouTube, a ball is dropped in front of a meter stick and lit by a strobe light. A long exposure photograph captures the position of the ball at each evenly spaced flash of light. The acceleration of the ball can then be measured from the photo. Would you believe that you could throw an egg across the room without breaking it? Burn a candle underwater? Vicki Cobb's We Dare You! is a gigantic collection of irresistible, easytoperform science experiments, tricks, bets, and games kids can do at home with everyday household objects. Thanks to the principles of gravity, mechanics, fluids, logic, geometry, energy, and perception, kids will find countless hours of fun with the selections included in this book. If you would like to make a We Dare You Video, click here. Vicki Cobb is a member of iNK's Authors on Call and is available for classroom programs through Field Trip Zoom, a terrific technology that requires only a computer, wifi, and a webcam. Click here to find out more. MLA 8 Citation
Cobb, Vicki. "A Bouncing Ball Like You've Never Seen." Nonfiction Minute, iNK Think Tank, 5 Feb. 2018, www.nonfictionminute.org/thenonfictionminute/ abouncingballlikeyou'veneverseen. 
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