Did anyone else watch that show Minute to Win it? As I was trying to think of something the write my last physics blog post about I thought of one task in particular that contestants were asked to complete. The game was called “Tipsy.” To win, the contestant had to balance three soda cans on their edge by drinking some of the soda to the perfect level. The reason that this task is possible is because of physics and center of gravity. As the amount of soda in the can decreases, the center of gravity of the tilted can shifts as the weight of the can changes due to less liquid, and eventually it is able to align with the vertical line up from the balanced edge of the can. So I was going to just attach a video of the "blueprint" for the task but I found a video of a bunch of college students getting real hype about it so I decided to include that instead:)
A couple of years ago, my family traveled to San Francisco and one thing we did was see the Golden Gate Bridge. To my disappointment, it was not that bright red that you might see in pictures. Anyway, the Golden Gate Bridge is a suspension bridge that is about three miles long and crosses the San Francisco Bay. With such a massive structure, one might wonder, how on earth does it stay up? Well, it has to do with the “suspension” part. By connecting cables to the middle of the bridge, up to towers, and back to the ends of the bridge, it decreases the force of the weight of the bridge in the middle, by creating a force upwards from tension. This way, the middle of bridge doesn’t collapse, and the bridge stays structurally sound. Unfortunately though, the suspension cables don’t protect the bridge from getting destroyed in a multitude of movies.
Everyone knows that it’s a nightmare to drive in New York City, even if you don’t drive yourself. When I was there last weekend, because we flew there, we had to use cabs and the subway to get around. We encountered many shall we say…interesting drivers. One was yelling at the other cars in a different language, but one of my favorites was the one who thought it was a good idea to drive 60 mph down the streets of Manhattan at 11:30pm. This made for a thrilling trip back to our hotel. Unfortunately for the driver, and us, there were other cars on the road at the time, and people, and stoplights. This meant there were a lot of sudden stops. As stated in Newton’s first law of motion, an object in motion tends to stay in motion, even if it’s in a small metal deathtrap of a car. So when the cab came to a sudden stop, us passengers wanted to continue moving forward at 60mph. So when we wanted to keep moving forward, the seat belts provided a force in the opposite direction, keeping us in our seats...and the car. Let’s just say thank goodness for seat belts.
I’ve already talked a bit about the show Sherlock, but I realized that there is a lot more physics involved to talk about. In one episode, called His Last Vow, Sherlock is shot in the chest. It’s a bit complicated to explain, but in the moments of shock following, he processes what he has to do in order to stay alive. The first decision is whether to fall forward or backwards. Because the bullet didn’t go completely through him his best option is to fall backwards to reduce blood loss. However, because of physics, and conservation of moment, wouldn’t he fall backwards anyway? It would be like those bullet and block problems that we did so much in physics last year. If the bullet was moving toward Sherlock, and he was facing the shooter, because of the velocity and direction of the bullet, and Sherlock’s stationary position, when hit, the momentum of the bullet would push him backwards as well. Maybe the bullet’s momentum wouldn’t be enough to do so, or maybe, the Sherlock writers didn’t think enough about the physics.
This past weekend my family flew to New York City, and as I thought about all the blog posts I had left to write, I tried to figure out what I could write about. And then, as we were landing, I realized that there was a lot of physics in the way a plane stops. Planes are able to travel at extremely high speeds and stop fairly quickly. What I didn’t know though, was what was used in planes as a braking system. It turns out that this can very with different planes. Some use a reverse thrust system, which means that the engines will kind of work “backwards.” By applying a force backwards, the equal and opposite reaction is for the plane to slow down as two forces work against each other. There are also speed brakes on the wings of the plane, which are the parts that flip upwards when landing. These increase drag, which also allows the plane to slow down.
When playing tennis, one way to control your shots is by putting spin on a ball. Tennis players do this by applying a force to the ball in different ways. This produces a different torque on the ball, changing its path after it bounces. If a ball is hit “flat” it is pretty predictable that the ball will bounce back at the same angle that it landed. To eliminate some of this predictability, a player can hit different shots that add top spin and back spin. When a player is at net, and their opponent is on the base line, a smart decision might be to hit drop shot. When a drop shot is hit, the torque is applied downward at an angle, which causes the ball to travel forward, but spin backwards. This means that when it lands and bounces back up due to its momentum, the ball will bounce back up, but more away from the opponent and back towards the net. By using physics and torque, tennis becomes much more interesting to play and watch.
As string player, one way that we can change the sound of the instrument is by playing “col legno.” This means that instead of using the side of the bow with hair on it, sound is made by bouncing the wooden side of the bow on the string. This provides a less lyrical and quieter sound. The reasons behind this change in sound are because of physics. The wooden side of the bow has a smooth surface, which contrasts the surface of the bow hair greatly. Bow hair has tiny grooves in it, which is ten covered in rosin to make it stickier. The wooden side of the bow does not have this. Therefore there is less friction between the surface of the string and the back of the bow. Because there is less friction, the force from the bow that acts on the string to make sound is much less as well. Because of physics, string players are able to change the sound of their instruments.
Who didn’t jump off swings when they were younger? Even as little kids, we knew that the best time to jump was when the swing reached it’s greatest height. By doing so, the maximum amount of gravitational potential energy is converted into kinetic energy when the person becomes a projectile. At a higher height, the velocity of the projectile is greater. If one were to jump off a swing at a lower height during its oscillation, the angle of projection would also be smaller. This could possible lead to the person landing underneath the swing, only to be hit in the head when the swing comes back, because it is an example of simple harmonic motion. So, whenever you’re on the playground, remember your physics, and avoid head injuries!
The other day, my seven year old cousin asked me, “how do bubbles work?” and I didn’t really know how to answer. So, I decided to answer her question in a blog post, or at least try to (even though she’ll never see it). It turns out the science behind soap bubbles is a bit complicated and there’s a lot that can be talked about but I think I’ll just focus on one part for now. Did you ever wonder why bubbles are always spherical? Laplace’s law states the larger the vessel radius, the larger the wall tension required to withstand a given internal fluid pressure. In the case of soap bubbles, the soap film minimizes its surface area, and by doing so, minimizes the surface tension of the film. The shape that allows for this minimal surface area is a sphere. I know this is a bit convoluted, but who knew bubbles were so complicated?
If you happened to read the previous post about tire swings, hi, I’m the short friend! Anyway… I also noticed that the tire swing was a perfect example of physics in the real world. Tire swings are an example of simple harmonic motion, a pendulum to be exact. When the tire is lifted to a certain height and let go, it swings back and forth, ideally at the same height each time. However, because this is not a perfect world, and factors such as air resistance came into play, this was only somewhat true. Also, with pendulums, the weight of the object on the end of the string/rope does not affect the time it takes to make one “revolution”, only the length of the pendulum. This means that in theory, it would take the same amount of time for a certain 6 ft 2 in person to make one revolution on the tire swing as a person half her height.
When you think about string instruments and physics, the thing that most people think about is the vibration of the strings to make a sound. Notes can be changed by placing fingers at certain intervals to change the length of the string. But another way to change the sound of a violin, is by using a mute. A mute is most commonly made of rubber, and attaches to the bridge of the string instrument. When attached, it adds weight to the bridge and changes the fundamental frequency of the bridge, which also vibrates when the instrument is played. The result is a softer sound, and a muted tone. In orchestra’s mutes are often used when there is a soloist playing with the ensemble. By using mutes, the full orchestra can still play without overpowering the soloist. However, some instrumentalists prefer not to use a mute because it changes the tone quality. But in other cases and for other instruments, mutes are used for different music genres resulting in a greater variety of music possible.
Over the summer, I had to chance to take a surfing lesson. Surfing requires balance, and coordination, so I was not particularly good at it. One very important aspect of surfing was going from laying down on your stomach, into a standing position. When doing this, it was very important that you were in the right part of the board, so that you were at the center of mass of the system. If you were too far back on the board, the force of the wave moving forward could pull the surf board up and out from under you throwing you backwards. It was also important to keep your body, and center of mass low. If you stood up completely straight, and then moved from the center of mass, the torque experienced by the surfboard system will be greater because the “radius” from the axis (the height of your body) is greater. So based on physics, I shouldn’t have had too much of a problem with surfing, oh well.
Recently we talked about flux and Gausses law. One thing that flux was compared to was the air of a fan hitting a wall. This could also be applied to sailing in a similar sense, even though it doesn’t involve electric fields. Electric flux is the electric field multiplied by the surface area of the plane the e-field is traveling through. When wind hits perpendicular to a sail, the force causes the boat to move. When it gets particularly windy, to prevent the force of the wind from causing the boat to keel over, the mainsail can be shortened. The action of bringing the sail down lower decreases the amount of surface area that the wind can push against. By decreasing the surface area of the sail, the “flux” will also decrease. So even though this isn’t exactly the same, the concepts are similar.
So I’m sure you’ve all seen it, but if you haven’t you should. A couple weeks ago, the Buffalo Bills kicker was seen on the sidelines slamming his football helmet to the ground after missing a field goal. After doing so, the helmet bounced off the ground, and hit him in the face. I won’t pretend to know anything about football, but I did see this, and I’m not going to lie, I watched the video multiple times. But this embarrassment could have been avoided if he had just known physics and been familiar with conservation of momentum. Momentum is equal to the mass of an object times the velocity, and conservation of momentum states that the momentum of a system is constant. So whatever velocity the helmet was thrown, is the velocity that it would bounce back up with. Because he was pretty angry, I’m guessing the force he applied was quite large, making the velocity pretty large also. So the result of his action could’ve been predicted. He should’ve studied more physics in college…
Canoeing is an activity that requires a lot of upper body and core strength, that and kayaking. When you use a paddle to propel an objet, you are applying newton’s laws of physics. Newton’s second law of physics states that acceleration is dependent on mass and the force acting on the object. Newton’s third law states that for every action there is an equal and opposite reaction. Both of these laws can be seen in canoeing. When the paddle is placed perpendicular to the water, and a person pushes against the water in the backwards direction, the result is the canoe moving forward, opposite the direction of the force applied as newton’s laws state. And like everything else, the greater the force applied, the greater the acceleration, and the greater the velocity. So next time you go canoeing or kayaking you’ll know that physics is the reason paddles work!
Bungee jumping is something that I would never do myself, but it involves a lot of physics in order to keep everyone safe and more importantly alive. Bungee jumping is a good example of simple harmonic motion. Bungee jumping companies have a variety of cords so that people of different weights can take the jump without hitting the bottom. It’s similar to the egg drop lab that we did, but with different variables, and the height of the drop being the constant. Because people have different weights, they will exert a different force on the cord when they pass the equilibrium point. Hooke’s law and conservation of energy could be used to make the correct calculations. Because F=kx, by knowing the elasticity of the cord, it can be determined what length the cord should be to accommodate the force of the person that is jumping. The heavier the person, the shorter the cord, or the greater elasticity of the cord needed.
One of my friends is absolutely terrified of riding bikes because she says she feels like she’s going to fall off. However, falling off a bike is pretty hard, not “as easy as riding a bike,” and the reason is because of physics. Initially I thought the physics behind riding a bike was easy also. I thought that the reason bikes are so stable is because of the forward momentum that comes from the velocity of the bike, which makes sense why it's hard to stay upright at a slower velocity. Before writing about it though, I wanted to check my understanding. I found this video that showed me that it’s actually much more complicated. I learned that a bike could stay upright even if there is not one riding it, because of physics. When a bike is moving and it begins to lean to one side, it also automatically steers to one side so the wheels end up moving back underneath the center of mass keeping it stable and upright and that this is due to specific structural aspects. So really, my friend has nothing to worry about because physics is on her side!
With winter comes cold temperatures and winter sports. Ice-skating is just one of many different winter sports that require attaching ourselves to small blades and boards. Ice-skating involves a lot of physics, both basic and more in depth. Simply put, ice skating works because of the low amount of friction between the ice and the blade. The low amount of friction means that the force of friction slowing the skater down is minimal. A person can gain speed by applying a force to the ice through the blade. This perpendicular force to the surface of the ice allows speed to be gained easily. The greater the force, the greater the acceleration, and the greater velocity that can be achieved. Another interesting part about figure skates is the shape of the blade, flat on the bottom with sharp edges. The flat area allows the skate to glide on the ice, and the blade allows the blade to dig into the ice and change direction, which makes ice-skating relatively easy. One thing that is still a bit unclear is why it's easier to walk on ice on tiny little blades than in shoes…
This sounds dark, I know, but after watching the most recent episode of Sherlock this is one of the lines that stuck with me. "It's not the fall that kills you, it's the landing." And I realized that there must be physics behind it, and of course there is! The best part is that the physics behind it makes a lot of sense. If you are familiar with Sherlock, whether the to show or the Sherlock Holmes books, you are familiar with the Reichenbach Fall. In the show, this occurred in the city of London, with Sherlock jumping to his "death" and hitting the street below. When a person or object falls, it reaches a point where it's velocity reaches terminal velocity. Then it continues to fall at the same speed forever, that is, until something gets in the way. It's not the fall itself that is harmful; it's the sudden deacceleration of the object as its velocity changes from terminal velocity to zero in an instant. And it's this huge acceleration over a short time that causes the harmful force when a fall is stopped because force is equal to mass times acceleration.
As the temperature drops, and snow accumulates the risk of cars slipping on snowy roads increases. This hasn't happened yet here but it's sure to soon. The solution to this winter dilemma is snow tires. Snow tires have deeper and more “ridges” (that's a technical term), which allows for greater traction. On regular tires, snow and ice can buildup on the surface, which prevents the tire from having direct contact with the road, therefore reducing the coefficient of friction and the ability of the driver to control the vehicle with ease. Snow tires are designed to prevent the buildup of ice and snow so there is more direct contact between the tires and the road. So to answer the question, we need snow tires because they increase the coefficient of friction between the tires and the road which allows for more direct control of the car's movements.
Skiing is not just riding the chairlift up the hill, standing at the top of the trail, pointing your skis downward, and going, there's much more to it than that. Whether it's in the olympics or recreationally, skiers like to go fast, and know exactly how to do it. One way to increase speed is to cut down air resistance. To do this, skiers will tuck their body and bend their knees so that they are lower and closer to the ground. That way, there is less surface area for the force of air to work against. Another way to increase speed is to start with a large force. This can be seen very clearly in competitive downhill skiing like in the olympics. When the skier leaves the gate, they push off with a force so that they can begin to accelerate down the mountain. If they don't get a big enough "push" at the beginning it can affect their whole run. On the contrary, another part of skiing is staying in control, which can be attributed to friction. Friction between the skis and the slope allow the skier to control their direction and their speed of they need to.
As a short person, sledding has always been difficult for me. Going on a sled by myself, I could never go as fast as people with greater mass because I couldn't get the same momentum. But that wasn't the worst thing. The worst was going on a sled with someone else bigger than me. I always had to sit in the front of the sled. And that means getting hit in the face with chunks of ice and snow as we go barreling down a hill at speeds I wasn't used to. As unfortunate as it was, it had to be done because physics was working against me. When you sled down a hill, the center of mass of the sled-person system changes because of the decline of the surface. When you are sledding with another person on the same sled, if the person with more mass sits in the front, the center of mass shifts farther forward. This is a problem because then, the sled could easily flip over forward. So I, as a small person, will continue to sit in the front of the sled, so as to keep the sled balanced, and prevent a horrible sledding disaster.
This past weekend a fellow orchestra member went to perform in the area all state orchestra for junior high students. These ensembles are made up of students that auditioned during solo fest and received the highest scores in the county, area, or state. This got me to thinking about the times that I had done the same thing, and the places the concerts were held. For area all state at the junior high level they hold the concert at high schools in the area, but for all county high school ensembles, the concert is at Eastman in Kodak Hall. I distinctly remember one time a concert that was held in the gymnasium of one of the schools. But who cares? This brings us to acoustical engineering, specifically architectural acoustics, which has to do with controlling and manipulating sound waves. Musical performance halls are specifically designed to minimize the amount of reflected sound waves. They can do this by getting rid of completely flat and smooth surfaces or adding sound absorbing materials like different fabrics. The reason for doing this is to prevent the formation of standing waves that can then produce different resonance. This can obstruct the sound coming from the musical instruments. The reason that a gymnasium is not an ideal place to hold a concert is because there are too many flat surfaces for sound waves to reflect off of, creating a less clear sound. So what’s the difference between a gymnasium and Kodak Hall? Acoustical engineering and Physics:)
It's November now, and here that usually means snow. However, the weather has been a bit unusual lately and the leaves are still falling. Which brings us to the physics of falling leaves. It's a little more complicated than "leaves fall because gravity." This is true, but as we learned more this year, there are other forces acting on leaves in addition to gravity. In addition to the force of gravity, falling objects like leaves are affected by air resistance. Air resistance acts on an object in the opposite direction. Air resistance is the reason that a leaf does not reach the ground the same time a rock does when they are dropped at the same height. Like in the lab that we did with the coffee filters, leaves don't take long to reach terminal velocity, the velocity at which the force of air resistance is equal to the force of gravity. When this happens, the object falls at a constant speed, and does not accelerate. This is why leaves float to the ground instead of plummeting to their inevitable seasonal death.
Another movie that I've seen recently had a lot more to do with physics. In the movie Gravity, Sandra Bullock and George Clooney (I forget their characters' names...oops) are astronauts that are working on the Hubble Telescope. In the whole movie, there was one scene that really stuck out, probably because I find it absolutely terrifying. When they are working on the telescope, another satellite in orbit is destroyed, and the pieces start to fly towards them. Sandra Bullock is attached to a crane-like arm, that is torn away from the telescope when a piece of shrapnel hits it. As a result from the force, the arm begins the spin around at extremely high speeds, whipping Sandra Bullock around and around. She is ordered to detach herself from the mechanical arm which she then does. Because of the rotating motion that her body was already experiencing, after she was detached, she continued to spin around head over heels into outer space. This is a classic example of newton's first law of motion, which states that an object in motion will stay in motion unless acted on by an outside force. Yes, it is the scariest thought, and yet it is proven by science that you could get lost in space. Have no fear though, Sandra was saved by George, who later *spoiler alert* sacrificed his life for hers. If that had not happened though, she would have had to throw something to get her moving in the other direction back towards the telescope, if she couldn't then she could have continued to spin forever because there wouldn't be any forces to stop her. And that has been the physics of getting lost in space, kind of.
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 firstname.lastname@example.org. Licensing of the content of APlusPhysics.com for other uses may be considered in the future.