If a tree falls in the forest, and no one is around to hear it, does it make a sound?
When a ball hits the ground or an axe hits a tree, we can hear a noise signaling this collision. Obviously, sound waves are produced, but where exactly do they come from?
When two objects collide, one of two things can happen: an elastic or inelastic collision. In the case of elastic, no kinetic energy is lost. Inelastic, however, involves a loss of kinetic energy. Where does it go?
Part of it goes to heat, but another part of it causes the sound waves to be produced because they need energy. When two objects collide, the molecules of the object vibrate a little, which in turn vibrates the air molecules, creating a longitudinal wave.
So, if a tree falls, it does make a sound because the laws of physics don't stop just because there isn't a human to watch it.
I was wondering how a credit card (without a chip) might be able to store the data needed to make a purchase, so I decided to look it up. As with most things, it actually is related to physics.
I knew that the strip was a "magnet", but in reality, it's several magnets (by several I mean a lot) that are polarized with north and south on differing sides. The strip stores the data you need with these magnets. There are three separate tracks on the magnetic strip that all store different information in almost a sort of magnetic code. When you swipe your card, the card reader decodes your own magnetic "code", allowing you to make a purchase. Neat, right?
Makeup is one of my biggest interests, however I wake up late a lot of the time and don't have time to put it on. It's fun to be creative and almost create art on your face, and to show it off for a day.
The big physics principle behind makeup is trying to combat the force of gravity and using friction to help the makeup apply.
All the makeup on your face is applied with some amount of friction helping you out. Whether you're applying lipstick from the tube or using a brush to put on eyeshadow, you're counting on friction to put that stuff on your face.
You also count on that force of friction to keep your makeup on your face throughout the day. If there was no friction, the makeup would fall right off your face.
(Below are some selected favorites from my collection which all demonstrate this physics principle. Also, my cat Mia is a diva and had to be in the photo.)
This is vaguely about physics but hey it's still related to physics. I wore my physics hat (thanks Mr. Fullerton) to a student council conference. I had a few friends joke about it on the ride there (calling me a nerd as your friends do). When we got to the retreat, however, it was actually cool how a few people I talked to asked me about the hat. They asked if I was taking physics and if I wanted to major in it (yes and yes), and I ended up having a cool conversation with a girl about particle physics and astrophysics over our lunch. We talked about the article I had read about a new planet forming and also particle accelerators. Overall, it was cool to talk to people about something we do everyday. I'm looking forward to going to college and meeting new people with the same interest in physics.
There are two types of colors in the world: additive and subtractive.
Additive deals with the source: sun, stars, and light bulbs for example. These light sources mix red, green and blue wavelengths to produce white light. If you were to spotlights that slightly overlap one another of those three colors, where all three overlap would create white light.
Subtractive deals with objects that reflect light, so anything that isn't a light source itself. Consider your favorite shirt. Mine is red. When I wear my red shirt, or whatever color yours is, my shirt is actually absorbing every other color except for red. So technically, your shirt (or mine) is every color except what we perceive it as! If your shirt is black, that just means it absorbs every color.
I'm not talking about cannonballs like what you shoot out of a cannon. That's obvious, a huge object is hitting you at a large velocity therefore there's a huge force transferred to your body.
I'm talking about the cannonballs you do when you jump into the pool with your friends on a warm summer day. (Which we're all looking forward to after this winter).
When you jump into a pool, the water has some amount of surface tension to oppose objects from entering it. When you dive in with your hands out, you break that surface tension before the rest of your body enters, and so only your fingertips feel a force. When you do a cannonball, half of your body feels the force, leaving that stinging feeling.
This is also the reason why when people fall or jump off bridges, they often say the impact kills them (not drowning) because the surface tension applies such a huge force.
There are several ways in which cars demonstrate physics. For one, when you turn, hit the gas or brake, you can see the property of mass called inertia. Anybody or anything in the car tends to continue traveling in the direction the car was originally going in or stay still if the car was stopped.
Also, the physics behind tires show how cars move. As the tire spins, it uses the friction between it and the road to push the car forward. This is why in snow or mud, where there is little friction, the car cannot move.
Finally, the antenna and speakers work together to receive radio waves from the air and transmit them into your car as audible sound waves.
I'm sure several of us have ran around the house with socks on and tried to slide on wood or smooth floors.
Using what we know about friction, we can see that the equation is the coefficient of friction times the normal force, or mg. Since we are on earth, there is obviously a force from gravity and a person has mass. Therefore, the explanation for this fun trick must lie in the coefficient of friction. Since you can slide a decent distance, the coefficient must be small, therefore causing the whole force from friction to be small as well.
I work at the bar, Murph's, on Friday and Saturday, and one of my tasks is to refill ketchup bottles. In order to get the ketchup to the neck of the bottle, I hold it by the bottom and spin it in a vertical circle.
This works because of centripetal force. You might be saying, however, that centripetal force pulls objects towards the center of the circle. While this is true, it acts on less dense materials at a greater magnitude. Inside the ketchup bottle, there is only air and ketchup. Since air is less dense, it gets pulled towards the center, displacing the ketchup.
My bird, Tucker, has a swing in his cage, and the way it is hung up makes it act like a pendulum. The length of the swing is 15 cm, or .15 m, and since it is obviously on Earth, the acceleration due to gravity is 9.8 m/s^2. This allows me to use the equation for period of a pendulum. This gave me an answer of .777 seconds.
The only issue with this is that there is friction between the cage and the swing. This causes the swing to slow down and come to a stop eventually.
Last night, I went out and saw the movie Split. I was slightly intrigued by the reviews, and it was said to have a really surprising ending, so I put aside some of my personal opinions on the topic of choice and watched it.
It was a very interesting movie to say the least, and if you're planning on watching the movie, I would stop reading here, because in order to get into some physics I have to spoil the ending, which is entirely the best part.
Okay, now that you're sure you want to continue, the movie is about a man with 23 distinct personalities inside him, which all take control at different times. While one, Barry, is in control, he kidnaps three girls. Three of the personalities (Barry, Ms. Patricia, Hedwig) believe in a figure called the Beast. The spectators find out that the Beast is not a figment of their imaginations, but actually a 24th personality that has super powers. Just by switching to this personality, the man's body becomes impenetrable and extremely strong.
The only surviving girl, Casey, tries to shoot him with a shotgun and the bullet essentially bounces right off. That's where the physics comes in. How much force would a regular shotgun shell impart, and how strong would this man's skin have to be?
A 1 oz. shotgun slug leaves the shotgun at 1800 fps, or about 550 m/s. This slug would weigh about .03 kg, giving it a momentum of 16.5 kg m/s. Assuming that the bullet was only in contact with his skin for .001 seconds, and it was a perfectly elastic collision, the force imparted onto his skin would be 16500 N. The only metal I could find info on was steel, and it can withstand 40 kN, meaning that his skin could withstand atleast half the force steel can.
Personally, I don't like fishing and I believe that if you aren't going to eat the fish it's cruel, but I was playing Stardew Valley and I had been doing a lot of fishing when I started thinking about the physics of fishing.
If a fish is on the hook, you start to reel in the line. As you do this, you created tension in the line. If the fish is able to produce a larger force in the opposite direction of this tension, the line will unroll a bit more. However, if the tension in the line is creating a bigger force than the fish can exert in the opposite direction, you will be able to reel in the line more and the fish will accelerate forward.
While doing this, you are also working against the force of friction from the fish and water, so you have to be careful not to snap the line by creating too much tension.
Hanging a picture can actually show a lot of physics dealing with force and friction.
First, you have to hit the nail with a hammer into the wall. Each time you hit the nail, you have to overcome the force of friction between the wall and the nail to get it to go in further. The hammer rebounds back after hitting the nail and you feel the force in your hand.
Then, depending on how heavy the picture you hang is, the wall has to exert a force equal to m*g on the nail to overcome the combined weight of the picture and the nail. If it exerted a force less than mg, the nail and picture would slide down the wall, leaving you with a large crack. Any larger than mg and it would accelerate upwards.
If you have two nails, the picture can be better supported because the wall can split the same force between two, so for a heavier picture use more nails.
One equation in physics is torque, which is the Force applied to object to rotate it about an axis times the radius the force is applied at. Torque only takes into account the force perpendicular to a surface, because any other direction will not cause it to spin.
When you open up a laptop, either with a force at some angle or directly perpendicular, the force acting perpendicular causes a net torque and spins it about the axis.
The same can be seen on doors, and even books. Also, some caps that come on hinges, like a lotion bottle, can be described in this way. As long as some of the force is directly perpendicular, the surface will move in the way it is being pushed or pulled.
I had an incredibly weird dream the other night. I was driving with my mother and in front of us was a man on roller blades using two machine guns taped to his arms to propel himself forwards.
I was about to forget my dream all together until I started thinking if physics would allow such a thing to happen.
Similar to the way a rifle would recoil when a bullet is shot, the machine guns would recoil when the bullets are shot out of them. Normally, they are anchored to something so the recoil is hard to notice. However, the force exerted on the machine gun would then be exerted on the man, whose body would normally compensate and return the machine gun to its original position eventually. Since he is on rollerblades with little or no friction (it's my dream, I'm neglecting friction), the force would propel him forwards. And since he was firing them at a rapid rate, this would in turn propel him forwards at a decent speed.
So, while this is an entirely reckless, irresponsible and dangerous idea, it is physically possible to achieve.
I used to wonder why the pendulum in a grandfather clock was there, and I originally thought it was for purely visual interest.
Now, I realize that the pendulum acts as a pendulum to keep the clock working at exactly the right time. The pendulum has a period of 1 second and each time it swings left or right, it moves the clock through one second.
But what length should the pendulum be in order to keep time at 1 second?
The equation for the period of a pendulum is T = (2* pi) (L/g)^(1/2) and when plugging in the value of 1 s for T and 9.81 m/s for g, you get that the length of a pendulum to keep time correctly is about .25 meters.
One of my more recent favorite games has been Stardew Valley. It is essentially an updated version of the game Harvest Moon, which originally came out in 1997 on the Gameboy, which is what I originally played it on. It is a game where you inherit a farm from a dying relative, and you come to find it overrun with weeds, trees and rocks. You slowly clear it out, plant crops and adopt animals. You can also mine and fish, and you slowly build relationships with the people in the town by joining them at festivals or bringing them gifts. You also have the opportunity to start a family.
For the most part, the game seems fairly realistic. You have to bait your fishing rod, it takes alot of hits to chop down a tree and you lose energy the more you preform a task. However, the mine introduces something that really breaks physics in this game. The first mine you journey into have 120 floors, and when you reach the bottom you receive a skeleton key. Once you unlock the desert, you have the chance to open another endless mine
Two things here are the problem. One, this mine is truly endless, and at some point you would not be able to go any farther because you would hit the center of the earth and just burn up.
Also, you can find holes which allow you to drop down levels. Not a ladder, like how you progress most of the game. It is a literal hole you must jump down. I have seen someone jump down 11 floors at one time. Now, it does take away some health, but assuming that each floor in the mine is around 6 meters minimum, you would fall 66 m, meaning you would be falling at around 36 m/s by the end of your fall. This would surely cause a bone to break, but you come away unscathed.
One comment I received on a previous blog about backpacks was about a backpack literally breaking your back. I decided to do some research on the topic. It appears that a vertebrae in your spine can withstand about 500 lbs of force, which is about 2225 N of force. In order to do some damage to your spine, you would need to have a backpack weigh this much in newtons. This means that your backpack would have to have a mass of 227 kg, or almost 500 lbs to do real damage to your back.
To put this in perspective, I estimated that a relatively full 2 inch binder is about 5 pounds on average. This would mean the backpack would have to hold about 100 binders to do damage.
No only is it near impossible to fit that many binders in a backpack, and so you would have to have one specially made, but you would also have to have a group of people or even a small machine help you lift it onto your back in order to actually do the damage.
Long story short, I don't think a backpack will be breaking your back any time soon.
In the winter time it seems that everyone is shocking each other. I shock myself on every chair at school, I swear. The worst feeling however, is when I shock my cat. Most of the time it happens when I'm petting her.
The reason why is that when I pet her, I am picking up electrons from her. This gives her a net positive charge and myself a net negative charge. I don't know the magnitude of the charges but we would have equal and opposite charges, assuming I am not grounded and my body contains the electrons, the same with her.
When I go to pet her again, our net charges come into contact, and the shock comes from the electrons "jumping" back to her fur and leaving my body.
The same sort of thing can happen when you are wearing fuzzy socks or slippers. When you walk, you scrape electrons off of the fabric, and when you go to touch someone, the excess electrons jump onto them in the form of the shock.
Likely, part of the reason why you seem to shock more people during the winter is that you wear warmer shoes or socks during the winter, and these items act as better insulators, preventing the net charge on your body from leaving to the Earth.
For my birthday, I received the video game called Firewatch. You play as a man who went through some rough points in his life, and so you take a job as a forest fire watchman, and you do a little bit more for your boss, Delilah. As you explore your area of the woods, you climb up and down several rock walls using only a rope, and the ropes have been sitting out in the forest for at least three years. I have only seen the character once, and he appears to be about 250 pounds, or roughly 113 kg. I was wondering what the tension would be in the rope as you climb up at a constant speed. This is a fairly easy calculation, where tension would be exactly equal to mass times the force of gravity which is about 1107 N of tension in the rope. This seems slightly unreasonable that the ropes would not snap, especially with consistent use, as they have been weathered by the elements.
This photo is a screenshot from the game of how you climb the rock walls
I carry all of my school supplies around in my backpack at all times, and it gets pretty heavy at times. I have a binder for all 4 APs, 2 folders, 3 various notebooks, and other odds and ends to get me through the school day. After some light research, I found the average binder weighs 3 pounds, and since my notebooks have the same amount of paper, I'll assume they'll have the same mass. 3 pounds is 1.36 kilograms, and since the other odds and ends probably are around 5 pounds, I converted it to 2.27 kg. This adds up to 11.79 kilograms, which is 115.54 N. This means my back is producing this large of a force to hold my backpack up at a constant height. The straps also have to exert a large force, so make sure you have strong straps on your backpack!
I am ridiculously addicted to french fries. I don't have a specific favorite place or type of fry that is the best, literally any fried rectangular potato will do for me.
I ate some french fries today, and figured why not address the physics behind me chewing my fries. You produce a different amount of force with your molars than your incisors. Men produce about 150 pounds of force with their molars and 83 with their incisors. Females can produce 108 pounds of force with their molars and 57 with their incisors. I happen to be a female, and I chew fries with my molars, so I am going to use 108 pounds of force, or 480.41 newtons.
That's alot of force for a french fry! 480 N is about how much force it would take to lift a 50 pound weight at a constant velocity. I would struggle to do that, but I can produce that much force with my jaw with little effort.
This wasn't a very in depth look at french fry physics, but this was an incredible thing to learn in my opinion.
If you haven't noticed, I really love my kitten. I am proud to call myself a crazy cat lady in training, but lets not go to far into me, we're here for physics! And I already wrote an all about me.
Kittens jump around and run alot. I'm going to track my cats movement for 7 minutes (I like the number 7 so that's why I picked that) and talk about the general physics in her energy.
12:48 - Mia is standing on the ground at first. She then jumps onto my bed, increasing her potential energy. She then further climbs up the back of my shirt, and further increases her potential energy.
12:49 - Mia returns to the bed, decreasing her potential energy from my back. She tries to get into my food. Then she runs around the bed, at a velocity of probably 2-3 m/s, meaning she has some kinetic energy while she runs.
12:50 - Mia takes a trip to the litter. I won't go into further detail.
12:51 - Since Mia is back on the floor, her potential energy is back to where it was at the beginning. She's done a lot, so she gets a quick drink.
12:52 - Mia is again running, but this time on the floor, so she has less overall energy than when she was running around on the bed.
12:53 - Mia needed food. Being a physics subject is hard work, I guess.
12:54 - Mia jumps up onto the window sill, meaning she has increased her potential energy yet again. However, the window sill is lower than my bed, so she has not done as much work as when she jumped onto the bed.
12:55 - Mia runs along the window sill, giving her kinetic energy, and jumps onto the bed from there, increasing her potential energy, and then I pick her up, so she no longer has any kinetic energy, but her potential energy is much higher.
I'd like to thank Mia for being such a cooperative test subject and thank you all for reading.
As you would know if you have a kitten, they only get worse as they age. This is intensely true for my kitten, Mia. Not only does she constantly escape her room, but she has figured out that my computer screen is touch screen, and wreaks havoc on whatever I am doing on the internet by touching it.
I often have to pick her up to try to prevent her from destroying something. She only weighs two pounds, even though she is 13-14 weeks old. I don't have to do much work because of her size, but there is still some being done. 2 pounds equals about .91 kilograms when converted. T-mg = ma would be the equation used to see how much tension is needed to lift her, however there is a flaw in using this equation, which I will discuss later. When I plug in the values, assuming I'm lifting her at a constant speed, the tension would need to be 19.6 newtons in my arm or 9.8 in each of my arms. (Back to the kittens being bad, as I wrote this exact sentence she climbed into my McDonalds bag and started licking my french fries. Kittens are like babies but they move faster and can't really be contained.)
But its unlikely I lift her at a constant speed, so lets say I lift her at an acceleration of 1.7 m/s2, just to change it up a bit. Then, when plugging the values in, the tension in one arm would have to be 23 N or 11.5 N in each arm.
Back to the problem with this equation. It assumes that the mass of the string (or arm in this case) is negligible, which obviously isn't true since my arms do have mass. This means that my values are off, but this is a high school blog so lets just forget about it for now and pretend my arms don't have mass. Alright, now that that's taken care of, have a nice day!
I didn't realize we could write about ourselves until recently, so I'm gonna join the party and introduce myself. My name is Alaina, and I am a senior this year. I hope to major in Physics and Math in college next year, and honestly I'd like to go to University at Buffalo even though I'm applying to Ivy League schools. I work at Murph's Irondequoit Pub every Friday, and they really do have the best wings in town, but also the best bread. I'm addicted to it. I love cats, and right now we have four at my moms house, and one at my dads. My dad's cat is named Olivia, and he has two dogs as well, Toby and Bailey. The cats at my moms are named Pretty Kitty, Kaylee, Leah and Mia. Mia is my cat, and it's taught me a lot about responsibility because I have to take care of her myself and pay for her vet bills and food, etc. I am currently the President of NHS, and I am the Editor in chief of the newspaper. I also participate in Math League, Link Crew, and Student Council. I recently got a part in the school musical, and I'm really excited because I haven't done a musical since 8th grade. In my free time, I play video games or watch other people play video games. I play on my computer, and I think it's way better than an X-Box or PlayStation. My favorite people to watch are Achievement Hunter/Let's Play/Rooster Teeth because they're hilarious and they make even scary games funny. My favorite video games currently are Terraria and Payday 2, but I've been playing a lot of Stardew Valley, too. Well, there's a little bit about my life. Have a good day!
The pages of APlusPhysics.com, Physics in Action podcasts, and other online media at this site are made available as a service to physics students, instructors, and others. Their use is encouraged and is free of charge. Teachers who wish to use materials either in a classroom demonstration format or as part of an interactive activity/lesson are granted permission (and encouraged) to do so. Linking to information on this site is allowed and encouraged, but content from APlusPhysics may not be made available elsewhere on the Internet without the author's written permission.
APlusPhysics.com, Silly Beagle Productions and Physics In Action materials are copyright protected and the author restricts their use to online usage through a live internet connection. Any downloading of files to other storage devices (hard drives, web servers, school servers, CDs, etc.) with the exception of Physics In Action podcast episodes is prohibited. The use of images, text and animations in other projects (including non-profit endeavors) is also prohibited. Requests for permission to use such material on other projects may be submitted in writing to email@example.com. Licensing of the content of APlusPhysics.com for other uses may be considered in the future.