Twilight Sparkle, a purple unicorn, was sitting in her library, rather annoyed. Spike had left on a metronome after practicing his piano, its ticking driving her crazy. But moments before shutting it off an idea came to her. A pony named Leonardo de Pony had discovered that sound traveled in waves years ago. And some time recently another pony found out that the frequency of a wave, when multiplied by its wavelength, could be used to find the velocity of the wave. But nopony had thought to combine the two yet.
She then activated the magic in her horn and quickly came up with a spell to make the sound waves visible. She then levitated a stopwatch and a meter stick over to her. Seconds later the sound waves given off by the metronome became visible to the naked eye, but they were too fast to test on her own. ‘One more spell’ she thought. She powered up one more time and slowed time down, which she tested by turning on the stopwatch. It was similarly slowed. She looked at the meter stick and saw that the sound waves were slowed enough to see. The waves were .36m from each other and frequency was 944.44 hertz. By multiplying the two numbers she found out that the speed of sound was 340 m/s.
After writing the paper about her discovery of the speed of sound, Twilight went for a walk around Ponyville, which ended up with her in front of her friend Rarity’s house. She knocked on the door and entered after Rarity said “Come in.”
As Twilight walked Rarity was looking at herself in a mirror. The white unicorn with a blue mane and tail turned from the mirror and telling her friend “I always wondered how these worked.”
“I can help with that.” retorted Twilight. “I have just completed an experiment with waves. Light is a wave to so this should work as adequate explication.” She then levitated a ribbon to in front of Rarity. The levitated ribbon began to undulate like a wave. “This is how a wave of light travels through air.” And she slowly propelled it towards the mirror, but instead of straight at the mirror she sent it in at a 30◦ angle. Instead of bouncing straight back at that angle, it bounced of it at a 30◦ on the other side.
“When a wave reflects off a surface, it bounces at the same angle as it entered, at this case 30◦.” she then explained.
The two ponies went to Sugar Cube Corner, a local sweets shop when their friend works, for a celebration. As they walked in Pinkie Pie, the pink party pony with a poufy pink mane, said, on one breath
“Higirls!LookIcanbendthisstrawbyputtingitinwater!”with obvious excitement in her voice. She then dropped a straw into a glass of water on the counter of the shop, causing it to appear to bend it the water.
“Pinkie you aren’t bending the straw.” Responded Twilight, clearly used to Pinkies antics.
“Yes I am, look at it.” she responded cheerfully.
Rarity piped up and said “You’re going to have to explain this to her, like you did for me darling.”
Twilight levitated the straw out of the water and said “This appears to be straight now right?” Pinkies head nodded that it did. “But in the water it looks bent right?” Pinkies head once again nodded. “It’s because the light, when it enters the water bends, due to the speed of light in water being slower than in air. The light bends when it hits the water because of the speed difference. It can be expressed in the equation n1sinΘ1=n2sinΘ2, when n equals the index of refraction”
Rarity gave a blank stare, befuddled by the explanation, but “Ohhh now it makes perfect sense.” said the pink pony. No one questioned why. Pinkie is an enigma wrapped in a mystery surrounded in a conundrum.
After a few cupcakes to celebrate Twilight’s new discovery, from outside the shop, came a very quiet “is anypony in there?” Afterward a small yellow pegasus with a long pink mane walked in to the shop.
“Hello Fluttershy.” said Pinkie Pie after the shy pegasus walked in. Fluttershy jumped in the air, squeaking at the same time. She then landed with a thud.
“I’m sorry for being so loud.” said the pegasus.
“Not at all Fluttershy. You gave me an idea to explain another principal of waves.” She then levitated some toy blocks left out by the owners of the establishment, the Cakes, young children, and set them up a few inches from each other. “Now if a sound wave were to go between those two blocks what do you think it would do?”
“It would just go straight through.” answered Fluttershy.
“That is what you would think, But watch.” responded Twilight. She cast the same spells as she did earlier in the day, but removed her friends from the time slowing effect. She then dropped a third block on the table, causing a sound wave to go through the gap in the blocks. Instead of just going straight through as Fluttershy predicted it went into the gap and then expanded to fill up all the room behind the two blocks.
“That is called diffraction.” Said Twilight.
The four friends walked to the park, were Pinkie Pie decided to throw a party. She then pulled a large pink cannon out of nowhere, her party cannon. She then hit the button on top causing it to fire. At the same time, on the other side of a pond, a voice said “Git back here!” The four ponies looked up to see their friend, Applejack, chasing after an out of control farm cart. On it were three small fillies, the Cutie Mark Crusaders, screaming on top of it.
The party cannon fired a lawn chair too far and shot it into the pond, causing several small waves. Seconds after the three young ponies bailed off the farm cart as it plunged in to the depths of the pond, also creating several small waves. Twilight then decided that this was a good time to teach her friends about more wave physics.
“Look at the waves being made.” she said. Her three friends and the new arrival in Applejack, looked into the pond. Twilight continued to explain what they would see. “Waves are made out of crests and troughs. The crest is the high point and the trough the low.” The waves were colliding now, some waves being canceled out, others being amplified. “The trough is always the same distance down as the crest is above the plain. If a trough hits a crest the cancel out. But if trough hits a trough or a crest hits a crest, they are amplified because the amount of energy in it is doubled or halved.”
The five ponies walk through the town, looking for their sixth friend. One of the small fillies from earlier, Scootaloo, buzzed up to them on her scooter.
“She’s going to do it again!” said the small pony excitedly.
“Whose going to do what again?” asked Twilight, wondering at what was happening.
“Rainbow Dash is going to do another Sonic Rainboom!” Scootaloo responded. The five friends were already running in the direction Scootaloo had come from.
In the sky above a field outside of town, a cyan pegasus with a rainbow mane and tail hovered a mile over the ground. Out of the corner of her eye she saw her friends running out of town to see it. ‘Here goes nothing’ she thought to herself as she began to climb further in to the sky.
Back down on the ground the five ponies saw their friend climb higher in to the sky. Twilight figured that it would be a good time to once more teach her friends about waves and wave motion. “Pay attention to the mach cone that will form around Rainbow.” she said with confidence. Her friend was now triple the distanced in the air then she was before, and was looping around to begin her dive. After several seconds the mach cone began to form around her.
Twilight began to elaborate on the situation. “What is happing is the sound waves are getting bunched up in front of her and being more spread out behind her due to the massive speed she is moving at.” The mach cone continded to tighten around Rainbows body. “Eventually she will be going so fast that she will be going faster than sound waves. Then she will break the mach cone and she will create the Sonic Rainboom.” The mach cone grew tighter still. Then it broke, a mass prismatic explosion occurring at the point the sound barrier was broken. Trailing behind their friend was a glorious rainbow, similar to what she did in Cloudsdale earlier in the year. She then pulled out of the dive, skimming the ground before slowing down to see her friends. She then landed and trotted up to them. The day was complete, with everpony learning about physics.
