# physicsguy#1

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## Entries in this blog

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/

## 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.

## 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 slo

## Why trees sway in the wind

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 ti

## 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 b

## The Physics of Space Fights - attacking planets

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

## The Physics of Space Fights - Ships

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

## The Physics of Space Fights - Weapons

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 l

## 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

## How waters properties shape planets

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 bec

## Why heavy snowballs are better

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.

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

## We still need NASA.

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 stil

## The Physics of Tossing a Pizza

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,

## 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

## Boomerangs

Boomerangs were a highly effective weapon for the natives of Australia (called aboriginals). Today people picture boomerangs as curved sticks or peices of plastic that are supposed to come back when you throw them but never do. However the returning boomerang is likely just a creative development of the far more useful non-returning type. Boomerangs were used in hunting and warfare as an effective long range weapon and for hand to hand combat. A boomerang, effectively, is to wings stuck toget

## Atlatl!

After a few blogs studying futuristic weapons I think it's time to look at some ancient, even prehistoric weapons. One of the most interesting of the physics related weapons was the atlatl. The atlatl is believed to have been developed independantly on each of the six inhabited continents. The atlatl is a tool to throw spears further and faster than is possible by hand. With an atlatl a spear can easily be thrown at more than 100 mph and travel well over 100 yards. The atlatl was used in hunting

## Shoot Lightning?

Another weapon that is undergoing developmnt is a weapon to shoot lightning. This is the latest version of Nikolai Tesla's "Death Ray". The goal is to produce a weapon that can shoot electricity through the air at a particular target. The latest idea is that the weapon wil shoot a high power laser for a very short time which creates a path of ionized air (or plasma) which is a better conductor of electricity than normal air. The weapon then sends electricity along the path to the target. The ele

## Lasers/directed energy weapons

Militaries around the world constantly search for improvements to their weapons technology to give them an important edge over every other country. One weapon that could provide this advancement is the directed energy weapon. Directed energy weapons “shoot” energy (usually in the form of electromagnetic or sound waves) instead of projectiles. They work on the principle of firing a burst of energy in a very small diameter at a target. This generates intense heat that can melt electronics, cause p

## The Physics of Blogging

While writing a blog physics impacts in numerous important ways. The force of gravity holds me to the chair I am sitting in. My fingers apply a force to the keyboard. Newton's 3rd law dictates that every time a force is exerted on the keyboard the keyboard exerts an equal force in the opposite direction on my hand. The monitor creates photons which travel in waves from the screen to my eyes. The lights also create photons that bounce off my face strike the monitor and come back to my eyes creati

## Rail Guns

An electromagnetic rail gun, commonly referred to as a rail gun is an experimental weapon that could be used to fire projectiles at very high speeds. A rail gun is basically two conducting rails connected to a pulsating power supply. A bridge is placed between the two rails to complete the circuit. When current flows up one rail through the armature and down the other rail a magnetic field is created that pushes the armature toward the end of the rails. This is because the current creates a magn

## The physics of Statues

Statues are an excellent form of art that represent specific people. Because statues must be able to stand the sculptor must consider many important physics concepts in their creation. A persons center of mass is very high on their body so an exact replica of a person standing would fall over. For this reason sculptors usually give standing figures larger feat or legs to lower their center of mass and therefore stabilize their creation. They sometimes add other figures to lean against for the

## Popping Popcorn

Popcorn is one of the four main types of corn, the others being sweet, dent, and flint(indian) corn. Of these types only popcorn pops. This is because popcorn has a hull with the proper thickness to make it burst open. Inside a kernal of corn their is a small amount of moisture surrounded by soft starch. As the kernal is heated the moisture expands increasing pressure and eventually causing the hull to burst. This occurs when the temperture of the kernal reaches 347°F which causes the pressure a

## Elasticity in PVC powered catapults

PVC powered catapults work on the principle of elasticity. Elasticity is the tendency of solid materials to return to their original shape when contorted. This means that when the top of a PVC pipe is pulled back, an elastic force will attempt to return it to its original position. This means that if the pipe is pulled back and then released the elasticity will whip it forward launching the object. There are two main measures of elasticity, the modulus and the elastic limit. The modulus is a

## Why robots have trouble walking

When a human walks they move their center of mass out in front of their front foot then move their back foot forward to catch themselves. The faster a human walks or runs the further their center of mass is moved. Because of our previous experience we can predict where and when our back foot needs to go to catch us. This is why as toddlers we fall down so much, we don't have the experience to know how to catch ourselves. Robots have a similar problem. Because every step taken is slightly diff

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