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  1. username

    Tornadoes

    The physics of tornadoes is very interesting. It all has to do with pressure and angular momentum. When air is heated it expands causing the density to decrease. This decrease in density combined with the higher density air around it causes the heated pocket to rise. The surrounding air then rushes in to fill the void and a tornado is born. The tornado is perpetuated by its own angular momentum. To learn more check out http://outreach.phas.ubc.ca/phas420/p420_04/sean/
  2. username

    Bolas

    Bolas are another medieval weapon that have some very interesting physics aspects. Bolas consist of 3 balls attached to equal length strings joined together around a central axis. The thrower exerts a force on two of the balls causing them to rotate around the third. When the balls are released they revolve around the center axis until they impact there target. Then the rotational force is turned into linear force breaking the targets legs.
  3. username

    Mudslides

    After the devastating mudslide in Washington last month I decided to find out a little more about what causes mudslides. Mudslides occur when porous soil becomes over saturated with water and becomes to heavy for the soil beneath to support it. The mass of the soil increases as it fills with water causing a greater force to be applied to the lower layers causing the bottom of a hill to explode outward. The extra water in the soil also decreases friction causing it to slide more easily down a slope. Mudslides are most common in areas with porous soil which is usually caused by powerful storms that deposit sediment followed by dry periods in which the sediment dries. This creates a structure that is stable but is severely weakened by future rainfall. The problem is compounded if the trees in an area are cut down as seems to be the case in the Washington incident.
  4. With spring weather finally here there are lots of trees that can be seen blowing in the wind. They do this because the wind pushes air molecules against the leaves and branches exerting a force on the trees pushing them to the side. The branches bend with the force of the wind then swing back oscillating in harmonic motion to gradually return to their equilibrium position. If trees did not oscillate they would snap more often because a greater force would be exerted over shorter distance and time (meaning power increases)
  5. username

    Two-way mirrors

    Ever wonder how a two way mirror works. The concept behind a mirror that you can see through on one side but not the other is surprisingly simple. It all has to do with how light is reflected on the sides of the mirror. The most important thing to realize is that there is no difference between one side of the mirror and the other. Two way mirrors work because the observer on one side sits in a darkened room while those being observed sit in a brightly lit room. Most of the light waves from the bright room are reflected back but some get through the mirror and into the dark room. Very little light hits the mirror from the dark room to reflect back so an observer in the dark room does not see their own reflection but a dimmer image of what is going on in the well lit room.
  6. The final aspect of space fighting that I will discuss here is attacking another planet from space. Once we have destroyed or gotten past the enemies fleet an invasion force would attack the planet that they wanted to conquer. Attacking from space would be tremendously useful. It would be a simple matter to toss large aerodynamic "spears" down at the enemy. Due to conservation of energy, the gravitational potential energy the projectiles have at launch would be converted to kinetic energy in the spear causing our weapon to create devastating craters whenever they landed. Although there would be some losses to friction in the atmosphere this would be negligible. This would make it very easy to destroy a planets defenses, but actually taking control of the planet itself would be mush more difficult. Any invasion force that was sent down would have to stay there because of the difficulty in escaping a planets atmosphere. Therefore the invasion would have to happen very quickly and could involve only a small fraction of the invasion force (since most of the fleet is required to maintain control of the space around the planet and therefore can not enter the atmosphere.
  7. Another interesting question on the topic of space fighting is, What will the ships look like? Before we can answer this we must define the most important characteristics of a space fleet. First, the ships must be able to attack the enemy and have some defense against retaliation. Second, they must be maneuverable enough to dodge enemy attacks. And third, they must be in space. In predict that most of the ships will have weapons facing in all directions because turning in space is to difficult to be practical and having guns in all directions will make this unnecessary. Making the ships maneuverable is much more difficult. In order to turn the ships would need to be almost spherical and have engines on the far away from the center of mass to produce the greatest torque. The ships will likely have engines pointed in many directions so that they can accelerate in any direction. The third aspect, that the ships must actually be in space seems obvious but is important to consider. Once a ship is in space it is relatively cheap and easy to send it off into space to do battle. However getting the ship into orbit requires tremendous amounts of energy and imposes severe weight restrictions. To deal with this we could construct a staging ground where the ships could be assembled, and/or mine nearby asteroids for the materials needed to build and construct the ships on the largest of asteroids.
  8. If humans develop colonies we must plan for the possibility of armed rebellion/takeover on both sides. To prepare for this we should look at how space battles would be fought. First of all, explosives could not be used. Explosive devices, nuclear of conventional, are effective because they produce a shock wave that destroys the surrounding area. In space there is no air to push away so the energy of the explosion would dissipate harmlessly. Instead humans would likely use kinetic impactors, or lasers. Kinetic impactors are basically bullets that are shot at very high velocity toward enemy ships with the intent to pierce their armor and damage critical systems. The problem with these weapons can be seen by studying Newton's 3rd law, the energy imparted into the projectile would create a force on the attacking ship in the opposite direction which would make it an easy target for enemy ships which could predict this change in direction. An alternative weapon would be a high powered laser. Laser's have an advantage in space because they will effectively go on forever with very little diffraction. Unfortunately lasers shoot energy and therefore require large amounts of it which is hard to get in space. This means that only small lasers could be used. Also lasers create a lot of heat at the target, which is good, and the base which is bad. Without an atmosphere to distribute heat the lasers could only fire intermittently and even then would require large radiators to dissipate heat.
  9. username

    Flails

    The flail, also known as a mace and chain or morning star mace, was a late medieval weapon consisting of a short rod with a chain at one end attaching it to a heavy, usually spiked, ball. Flails were not used very often because an experienced enemy could easily step in close to a user making the flail useless. However the flail does have some interesting advantages that we can analyze with physics. First, the combination of rod and chain created a very long weapon that could create huge amounts of force since a small acceleration at the center creates a large velocity on the end. Second if an opponent attempted to block the flail and the chain hit their weapon or shield, the ball would whip around and hit them in the arm or head. This is because the momentum of the ball would not change but the radius of the circle it was moving along would decrease so it's velocity would increase. The most useful aspect of the flail was its unpredictability. Anyone not familiar with the weapon would not anticipate the strikes from behind that the chain creates. skip to six minutes to see the flail in action
  10. As we all know water changes the face of our planet in dramatic ways. Rivers can blast paths through the ground with remarkable speed making their way to massive oceans. But one of waters unique properties is even more useful in changing the shape of the earth. Unlike almost every other material water expands when it changes from a liquid to a solid. This is what causes icebergs to float. It also prevents most of the earth's surface from being covered in big rocks like other planets. This is because when liquid water seeps into the cracks in a rock and freezes it expands cracking the rock and eventually creating soil. Other planets with different liquids do not have this property and therefore have surfaces that are covered with boulders.
  11. Ever wonder why heavy snowballs fly so much further than light ones? The answer is pretty simple. First lets assume that we have two snowballs that are the same size and shape but one is twice as heavy as the other. Also we know that each will leave are hand with the same velocity since our hand can only move so fast regardless of the weight in it and the weight of a normal sized snowball will not slow it down at all. To figure it out start by drawing a force body diagram for each snowball. The forces of gravity and drag act on each snowball. Note that the force of drag is equal for each snowball since they are traveling at the same velocity. Therefore using F=ma which we will rearrange into a=F/m we can see that the force of drag (which is the only force resisting forward motion) will produce a greater acceleration on the lighter object and therefore slow it down faster.
  12. username

    Faraday Cages

    Faraday cages have a variety of uses in the modern world from repairing high voltage power lines to protecting government secrets. Faraday cages shield their contents from static electric fields. A Faraday cage is effectively a conducting shell that distributes any charge around the edges. As we can see from Gauss's law Flux = Qenc/E0 if we have a conducting shell with no charge inside their is also no electric flux inside. This means that you can put massive amounts of charge on the edge of the shell without having any charge make its way inside. This is very useful for people working with high voltages because they can completely enclose themselves in conductive materials (usually similar to chain-mail) they are able to touch charged wires without being hurt. The same principal protects people inside of airplanes and cars when these vehicles are struck by lightning. Governments use this idea by enclosing computers they want to protect in giant metal cages to protect the information they contain from radiation from solar flares and manmade EMP devices. Faraday cages can also be used to safely stand in front of Tesla Coils as seen here.
  13. With the new federal budget finally increasing NASA's funding I think its time to talk about some of the great things NASA has done and still does. NASA created the basis for many important products that we use today including memory foam, scratch resistant lenses, and water purification systems. Some people consider NASA to be unnecessary because of the advent of space entrepreneurship with companies like SpaceX sending shuttles to the ISS and putting satellites into orbit. However NASA is still relevant because they push the boundaries of what is possible, which currently means sending people beyond a low orbit to the moon and Mars. NASA will always be relevant because they are able to plan further into the future than any business is capable of doing. Currently they are working on the Space Launch System which will be the most powerful rocket in existence and are planning a manned Mars mission in the 2030s. To learn about some of the products that were created based on NASA science check out this site http://www.nasa.gov/externalflash/nasacity/index2.htm
  14. Tossing pizza dough is very important to get the proper thickness and consistency of dough to make a pizza with. It also helps with the development of better standing wave ultrasonic motors, but more on that later. Professional pizza tossers know and scientists have proven that the best way to toss a pizza from rest is in a spiral. This is because a large amount of torque is required to get the dough spinning and all the rotation it has will be created when it leaves the throwers hand. However, after the dough is spinning when the tosser wants to toss it again they should use a semi-elliptical motion so the dough flies through the air at an angle based on the condition it is in when it hits their hands. This is more risky because it is easier to toss the pizza incorrectly since each additional toss puts it further from a helical path which is why beginning pizza tossers only do one toss at a time. Pizza tossing is similar to ultrasonic motors since they both convert torque applied over a short time to continuous rotational motion. Scientist can measure details about the pizza's flight, such as the number of rotations, initial torque and angle of rotation to design better motors. Here are some really cool pizza tossing tricks. To learn more check out this link: http://phys.org/news158491566.html
  15. username

    Levitation

    Most people consider levitation to be possible only in fantasy worlds. However people can make use of the power of electricity to levitate/fly under certain conditions. To levitate there must be no net force on an object while the object is not touching the ground. On Earth gravity is always pulling down so we must find another force to counteract it and push up on the object that we want to levitate. Their are four forces in nature, gravity, electromagnetism, and strong and weak nuclear forces. Of these gravity is by far the weakest. Strong nuclear forces, fusion, provides the sun's energy and atomic bomb explosions. Weak nuclear forces are involved in radioactive decay. Although powerful, they are to deadly for levitation. Electromagnetism is also very powerful but much easier to control making it perfect for levitation. Unlike gravity electromagnetism can attract or repel meaning that by putting a charge on an object on the ground and one in the air a force can be created in the upward direction to counteract gravity (if the charges have the same sign). This means that by placing a charge on a person and on a platform beneath them we can make a person levitate. Unfortunately keeping the two objects charged is very difficult so right now it is not feasible to levitate people but if the technology develops and stronger magnets are made it could be possible to levitate in a controlled fashion for extended periods. This video shows some of what can be done now. (skip to about 1:40) If the bottom magnet could be spread out and the top one balanced without the rod the man would levitate. Obviously the magnets he uses are not nearly strong enough to get the full effect.

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