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Gravity

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jrwalther

Week 1

This week I focused on the first three chapters of Mechanics, the introduction, kinematics and dynamics.  I focused more on dynamics as I feel that is the area I needed more work on but both were very helpful.  

 

Areas that went well included most of the projectile motion.  Describing motion 1 and 2 were also just review as I knew almost everything covered.  Circular and relative motion was a little harder but it made more sense the more I sat down with it and compared it to translational motion.  It is very similar in how you calculate and derive expressions as well as equations you use such as converting kinematic equations by just replacing certain variables with their angular equivalents.

 

There were a couple of areas that I found to be more challenging.  One being Tension as it was always an area that I struggled with.  As I went through however I began to pick up tips on this as well that would help me.  One being to establish a positive direction right away.  The next being to draw free body diagrams of all of the forces affecting the Tension of an object.  After I got these things down it seemed to come a little easier.  Calculating friction was also something that I found to be challenging.  


My keys to success would include slowing down when I am watching the educator videos.  It helped me to slow down and pause here and there in order to catch up and make sure I understand everything that has been said to far.  I used this the most during derivations as it helped me understand each step of it.    

jrwalther

I am a black belt and I always enjoyed the physics behind karate as they are often more complicated than most people first think.  When two people line up to fight, they both bring a certain amount of kinetic energy to the fight.  This is determined by their weight, height, muscle strength and also their physical health.  The main principle behind karate is to use your body to channel this energy and make maximum use of it.  It also focuses on how you can take away from your opponents with smart blocking a defense maneuvers.  We can often base the power of these punches on F=ma^2.  Since our mass is going to be constant it is important to find ways to increase our acceleration of the punch to generate more force.  When you combine this with the ability to channel and make most of your kinetic energy, you give yourself a huge advantage in any fighting situation.   

jrwalther

A golf balls dimples are often overlooked as just being a design that someone decided looked good when in fact they play a major role in the flight of the golf ball.  Ultimately, the dimples increase the drag of the ball slightly.  But another big effect is that they increase "Magnus Lift" which is a lifting force experienced by rotating objects travelling through a certain medium.  This lift is present because the ball often has backspin when it is driven with a club.  Golf balls flights are very different from most objects as they don't follow an inverted parabolic flight.  Their flight can be seen in the diagram below.   

Image result for golf ball flight

jrwalther

Bulletproof vests are becoming much more common as they are becoming very easy to conceal.  People are able to wear them under shirts and jackets and no one would ever know.  They are very widely used in the military and police and law enforcement work.  The vests are designed to disperse a bullets energy in order to minimize the blunt force trauma.  Their are a couple different types of body armor.  One of which is heavy body armor and is made of strengthened steel plates.  The only down side to this is that it is obviously very heavy and not always convenient to wear.  We are finding that today some bullets can even penetrate steel.  A more popular vest would be the light weight vests which are woven out of interlacing strands of Kevlar.  They work the same as the other vests as layers of this tough material deform the bullet and take away its energy during impact.  They are also much easier to conceal and are much lighter than hard body armor.

jrwalther

The are two main factors that affect a Frisbee during flight.  Gravity accelerates the object downward at 9.8 m/s.  In the air, lift and angular momentum act on it.  Lift is created because of its shaped surfaces while it travels through the air.  The reason a Frisbee flows so clean and far through the air is because the air flowing over the top of a Frisbee is much faster than the air flowing beneath it.  The Bernoulli Principle also describes why is maintains this flight.  It says how their is lower air pressure on top of the Frisbee than beneath it causing it to rise.  This principle is also the reason that planes take off, fly and land. So ultimately their are similarities between an airplane and a Frisbee.  While it may just look like a simple disk to have fun throwing, their is actually a lot of physics behind the creation and design of it.     

jrwalther

The water bottle flip challenge became very popular very quick but it is not just luck in getting the bottle to land upright.  When the bottle is moving through the air during its flip, the water begins to climb the sides of it.  This causes an increase in it's moment of inertia which in return, decreases its rotational speed.  This is very similar to a diver who extends his arms and legs in order to slow his spin or an ice skater.  The amount of water inside of the bottle also plays a major role in the success of it landing upright.  If the bottle is full, the water would be unable to climb the sides and it would give it a high center of mass.  That means when it lands, it would just topple over.  After experiments to determine the best height, it seems that filling it just below a third of the way produced the best results.   

jrwalther

Their are many factors that make a yo-yo spin showing they are actually more complicated than people may first think.  Gravity is an obvious force as it is what pulls the yo-yo down.  Friction is the reason that it unwinds and returns.  Without friction the yo-yo would not spin nor would it return to the starting position.  When it is at this starting position it is containing the potential energy to fall and spin.  This is then converted into kinetic energy when it starts its trip.  The yo-yo has the most kinetic energy when it is at the bottom and all the potential energy has been converted.  A major factor in a yo-yo is gyroscopic stability which is what keeps the yo-yo spinning in one direction.  it's axis of rotation does not change and is always perpendicular to the axis of rotation.    

jrwalther

The brain goes through lots of weird stages and experiences while sleeping that are very different from when you are awake.  For one, the brain waves slow down dramatically.  When awake the brains frequency is around 30hz and that drops to less than 3.5hz when the person falls asleep.  There are around 5 stages of sleep every time you go to bed at night.  The first stage includes a very light sleep while the second becomes slightly deeper.  The third and fourth stages are the deepest part of it and the fifth stage is where dreaming occurs and their is an increase in heart rate and eye movements.  Gravity also plays a role during sleep and is the force that pulls you to the bed and is the reason that sleep would be much different in zero gravity.  It would be much more comfortable as you would never have overlapping body parts and may be a way to a better nights sleep!

jrwalther

Video games are becoming more and more physics based in order to create a more realistic gaming experience.  Battlefield 1 is one of the biggest first person shooter video games out right now and they did not forget about the physics.  In call of duty sniping is very different from battlefield.  In call of duty their is no bullet drop so if you aim at someone and shoot you kill them.  That is not always the case in battlefield.  They take into account bullet drop and drag.  That means when using a sniper from long range you often have to aim above the person you are shooting at in order to account for this bullet drop.  It ultimately creates a much more realistic experience for the sniping element to the game.  It will also do this with heavy guns such as tanks and anti-aircraft weapons.   

jrwalther

I think that everyone knows how a hot air balloon works in theory but what are the basic physics behind it?  The basic concept of it is that it blows hot air into the large balloon at the top to create buoyancy which eventually causes the balloon to lift.  The air inside of the balloon is ultimately less dense than the air outside and this difference in density is also what causes the balloon to lift.  The principle behind this lift is called Archimedes principle.  This states that the upward buoyant force exerted on a body is equal to the weight of the fluid that the body displaces and acts in the upward direction.  This is the same principle that describes how boats stay afloat in the water. 

jrwalther

Push ups are probably the most common form of a workout you will see.  They are easy and can be done almost everywhere, but how good of a workout are they actually giving people?  There are different ways to do a push up but when done correctly, most people will be lifting around 65% of their body weight.  This would be when someone is doing the standard position of having their feet kicked out.  When a push up is performed on the knees instead of feet extended, we see that the amount of body weight they are lifting goes down by around 15%.  These percentages show how push ups can also be conformed around what each person wants.  Some can be putting in more of a workout while others can adjust their position in order to suit their needs or put in more reps.  

jrwalther

Physics of swimming

Humans are clearly not as well suited for the water as we are for land, just look at a human body.  We can't hold our breath for very long, and we get very tired very quickly in water.  The main reason for this is the difference between the water and the air.  The biggest difference between the two is that water is much more dense.  When a human walks on land, the main thing your body has to do is work against gravity and then friction between our feet and the floor.  Air resistance also becomes a bigger factor as wind increases or we pick up speed.  The main force opposing a human in water is drag or water resistance.  This can be controlled though by the way we move through the water.  The same way a cyclist tries to minimize surface area being presented to the wind, a swimmer wants to minimize the resistance to water they may be facing.  This is why many of the different ways of swimming are so efficient.  The different strokes used in competitive swimming and just to swim fast, are ways humans have found to effectively cut down on water resistance and drag.

jrwalther

Physics of solar energy

Solar energy is a growing demand in the United States as more funding has allowed this energy source to become much cheaper and more available to the average person.  They are converting the suns energy into electricity using solar cells.  This relies on the photoelectric effect which is the ability of matter to emit electrons when a light is shone on it.  Silicon is a semi-conductor which makes it a key ingredient in making solar cells.  Sunlight is composed of many photons and as these hit the silicon in the solar cells, they transfer the energy into loose electrons.  This knocks them right off of the atom.  After this, it is then needed to herd the stray electrons into an electric current.  They do this by creating an electrical imbalance within a cell.  Essentially a solar panel is just a big panel with lots of these little reactions going on in order to gain the electrical energy from it.   

Image result for solar panels

jrwalther

Physics of video games

Video games are constantly progressing in terms of how real they are becoming and the graphics.  Part of these games becoming more realistic is the implementation of physics into them.  The purpose of them is making everything appear more real to the viewer as if they were actually in the game.  One big part of this is ragdoll physics.  This is where bodies in video games appear more and more to have a realistic bone structure and similar joint movements as an actual human body.  This includes bodies as people are killed and fall to the floor. As we see bigger video games being made, we see lots more computing power go into these ragdoll physics.  This includes much more accurate simulations of solids, liquids and hydrodynamics.  These can then go on to represent the movements of muscles and tendons and other components of the body to make it eventually look like it is almost real life.  Soft physics is also becoming popular in video games. Soft physics is simulating individual sections of everything in the game instead of grouping them together so that each object behaves in a much more realistic, life-like way.

jrwalther

There is surprising a lot of physics that goes into a simple motorized bike.  Even something simple on it like the weight of the tires.  They are very important and in many cases can be the difference between you flying or stalling.  This is because of leverage on the bike and the wheel is basically just a round lever.  That means that the bigger the wheel and the more weight, than much more power is needed to move that wheel.  This could be needing a bigger motor as a whole or may just slow the bike down.  Another factor is the friction that goes into these bikes.  Friction drive can have both advantages and disadvantages such as ease of installation.  However it may not be able to be used in rain or wet conditions and the tires may wear done much faster.  That is where the designers of all these bikes have to decide the ratios they want or friction between all these factors that come into play.

Image result for motorized bike

jrwalther

Physics of Wind Energy

The purpose of a wind turbine is to turn the kinetic energy of the wind into electrical energy.  This is the idea of most machines as energy can only be converted, it cannot be created or destroyed.  Like any moving mass, the kinetic energy is calculated through the equation K=1/2mv^2.  For calculating the kinetic energy in a wind turbine we would use the wind speed for velocity.  The mass would be the particular volume of air.  You can also find the power in the wind a turbine is using to generate its electrical energy.  To find the power you would use the equation P=1/2 x air density x area x wind speed^3 x time.This shows us that the power of wind is dependent on 3 variables.  We see that the area affects the power showing us that location of these wind turbines will actually play a role in how much power is generated while the others cannot be controlled.  

   Image result for wind turbine

jrwalther

Paper airplanes are something almost everyone has made but most people don't really think about ways to make it better and why some are better than others.  The main factor in creating a successful paper airplane is making sure it is as aerodynamic as possible.  Limiting the amount of factors to create resistance will result in a more successful trip.  This includes making a tail that air will glide right over instead of getting trapped on.  The two forces acting against the plane in flight are drag and gravity.  Drag has to do with the aerodynamics of the plane as eliminating the factors to trap wind will help it and the way to fight gravity hurting your plane is to make it as light as possible.  The two forces helping the plane in flight are thrust and lift.  Thrust is the forward movement of the plane.  The initial thrust comes from the thrower and after that, it really just becomes a glider.  Lift is the air below the plane pushing up harder than the air is pushing down from above.  That is why the wings of planes are curved so that air moves more quickly over the top of the wing creating a upward push.

jrwalther

Physics of Catapults

Catapults are ancient weapons known for doing lots of damage from a far distance.  But how can a simple machine launch such big objects so far?  It comes down to the way the machine is built in which it creates large amounts of potential energy by either twisting a rope or flexing wood.  This potential energy is then transferred to the object when it is released.  One of the most common catapults is the ballista which is basically a giant crossbow.  In this the potential energy is stored in both the tension in the rope and the bent arms on the bow.  The tension in it acts as a spring so in can be calculated using U=1/2kx^2.  This is then converted into kinetic energy when the bow is released and that is where it is able to fire heavy objects very far.

Image result for ballista

jrwalther

Soccer shot

People who are new to soccer almost always begin kicking the ball with their toe.  It seems like the best way to shoot because of how much power you are able to gain.  What people don't realize is the control and accuracy that is lost when this happens.  The best way to hit a ball for both power and accuracy is with the inside of your foot because of the major increase in surface area you are hitting the ball with.  Kicking a ball with your toe makes it much more open to have spin that may be unwanted.  Striking the ball anywhere but the center will cause either top spin, side spin or back spin and you often have little control.  When you use more surface area with the inside of your foot you are able to get these same motions but with much more control as it becomes less likely of a miss hit. 

jrwalther

Physics of Fifa

A lot more work goes into creating a more smart life-like video game each year including Fifa.  A major break through in Fifa 14 was that they finally figured out how to make the ball sail smartly through the air. The engineers working on the physics of the game finally found the problem that was making the ball look like it was just shot in a linear path.  They found that their drag coefficient was broken.  This models air resistance  and affects the trajectory and speed of the ball when it is in flight.  In previous years the ball was violating the laws of physics by accelerating and decelerating at rates unaffected by the initial kick speed.  This fix also fixed the spin of the ball in flight.  Previously the ball would be spinning one way but would curve the other way.  With this new air resistance fix to the game, the ball now has realistic trajectory when it is kicked, a more realistic acceleration and deceleration, and a more realistic spin on the ball when it is in flight.  

jrwalther

Gravity

I watched a cool lab video on a professor giving a visual representation of gravity.  The idea of gravity has always been pretty easy for me to understand and easy to use in equations but where I begin to lose that understanding is when we leave earth and look at how it holds everything together.  How space is constantly expanding but these planets, moons and stars are constantly effecting each other.  In this video you get to see how gravity really makes these things work together to make space what it is.  The part I found coolest was when he explained and showed why all the planets are going around the sun the same way.  In this case it is clockwise and anything going the opposite way around the sun was or would be eliminated.  This was due to collisions and as he says, those going counter clock wise were not heading in the 'preferable direction'.

 

 

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