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zlessard
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Blog Entries posted by zlessard
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There are hundreds of ways to sustain an injury like a concussion. (getting hit by an object, falling on the floor, falling off of a tube, etc.) It may be strange to think about, but a concussion is truly caused by a basic physics concept: the law of inertia. Take the example of falling on the floor. When a head makes contact with the floor, the skull will obviously stop traveling in the direction of the floor. The brain, however, will continue moving until acted on by an outside force because it did not make direct contact with the floor. This causes the brain to keep moving until it makes contact with the skull, which causes the concussive energy to flow throughout the brain and ultimately lead to a concussion. So next time you fall off of a tube connected to the back of a speed boat and smack your head against the water at such a force that gives you a concussion, you can blame your misfortune on the fact that your brain is made up of matter and therefore influenced by the law of inertia.
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One of many peoples favorite athletes is NBA MVP Stephen Curry, and for good reason. Personally, I like him for his shooting ability, so I decided to look more into this facet of his game. Curry is one of the best shooters in NBA history, and he does so with a very technically sound shooting form. For starters, his right forearm (his shooting arm) is always nearly vertical, never deviating more then 5 degrees away from vertical. Something I find interesting is that he releases the ball as he is rising, making for a much quicker release. He consistently releases the ball .05 seconds before the peak of his jump. Standing 6'3, the launch angle on his shot is around 50 degrees, sometimes higher, allowing him to avoid getting blocked by taller defenders and still having an arc that goes in at a very effective rate. The higher launch angle can also be an advantage because it turns the 18" diameter hoop into a larger target for the ball to go through, because the ball approaches at a steeper angle. This allows for more area for the ball to go through. The most remarkable part of Curry's shot is how quick his release is, as he releases the ball in about .4 seconds every time, allowing him to get shots off even when defenders are close. All it takes is mastering the basic physics to Curry's jump shot and you'll be able to make a ridiculous amount of three pointers like the man himself.
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Everyone has heard about a tsunami, whether that be the one that hit Japan not too long ago or some other instance. Regardless of how you've heard of these water monsters, I was interested to find out more about the physics behind these.
Tsunamis are basically a massive scale version of the waves that we've studied throughout our physics experiences. Rather than wavelengths in centimeters and periods measured in seconds, the waves of tsunamis are measured in kilometers and their periods are measured in hours. Their wavelengths have been measured to be as large as 500 km. Interestingly enough, the speed that these waves travel at is dependent only upon the water depth and the force of gravity. In the ocean, water depth can be 5000m, and utilizing the equation that the speed of the wave = sq rt(g·H), that means that waves would travel 221 MPH at a depth of 5000m.
Tsunamis caused by earthquakes, however, have wavelengths and periods that are determined by the size of the underwater disturbances caused by the earthquake.
As tsunamis approach land, the water depth decreases, thus causing the speed that the waves are traveling at to decrease. The tsunamis energy flux, which depends on speed and height of the waves, remains almost constant. As the speed decreases and the energy remains constant, this causes the heights of the tsunami waves to become much greater as they approach land. Because of this effect, known as "shoaling", tsunamis can go completely unseen at water but grow rather tall as they approach land. This is why tsunamis are often characterized by their massive waves.
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Recently I saw a commercial for a phone that said that the screen of this phone could not be cracked. This got me thinking of all the stories that people have told me about their phone cracking and what truly causes this to happen. A few times I have dropped my phone and assumed that when I picked it up it would be completely shattered, but I was wrong. Why is it that a phone can shatter on a short fall, while other times it sounds as if it were hurled at the ground and it ends up without a scratch on it?
That question can simply be answered with luck. The likeliness of a phone to crack is dependent on where on the phone makes initial contact with the ground. If the phone falls directly on the face it is not very likely to crack because the impact is spread throughout the whole surface of the face. If a phone is dropped on its corner, the force of contact with the ground is much more concentrated in one area, making it more likely that the glass screen will not be able to survive the fall. A phone that falls from a short height and lands on its corner is more likely to crack than a phone that falls from a greater height and lands directly on the face.
The strength of a phone screen is dependent upon both the surface compression and inner tension of the phone. This strength determines how many blows the screen can take before shattering. Glass only shatters if the force of an impact is greater than the surface compression. So if a phone is only dropped from a short height, it is not likely that it will contact the ground with enough force to shatter the screen. You can't really measure the exact strength of a piece of glass because that is dependent upon the makeup of the glass, but you can get a pretty good idea of how strong a glass phone screen is.
The likeliness of a phone to shatter is also dependent on the surface that it lands on. It seems obvious, but a phone is more likely to crack on concrete than on a pillow because there is a greater force applied to the phone upon impact when it hits the concrete rather than the pillow.
So if you ever drop your phone and are worried as it falls through the air that it is going to crack, just hope that it falls directly on its face. Or, better yet, buy a good case for your phone. That way you won't have to worry so much about the ability of your phone to take the force of impact with the ground.
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Something that I've been noticing since I was a little kid is that on car commercials, when they are showing the car driving, it often times looks like the wheels are spinning backwards and the car is going forward. It wasn't until recently that this concept was explained to me. What really causes this is the fact that the frames per second of the video camera is slightly greater than the rotations per second of the wheel. This makes it so that in each new frame that is recorded, the spokes on the wheels are a few degrees short of the position that they were in for the prior frame. This causes the illusion that the wheels are spinning in reverse while the car is going forward. This is known as the wagon-wheel effect.
Also less commonly but maybe a little bit cooler, the wheel can look like it isn't moving at all. This is caused by the same concept, except the spokes of the wheels are in the same position for each new frame, meaning the frames per second of the camera is equal to the rotations per second of the wheel, or that they have a perfect rotational symmetry. This effect is evident in the clip of the helicopter, as the rotor blade spins in a similar way to a wheel on a car. (for more on helicopters, look at my previous blog post)
If you haven't noticed this before, look out for it the next time you're watching a commercial or a movie. There's a good chance that you could notice the wagon-wheel effect, in effect.
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