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Gravity

## Week 3

This week I focused on chapter 5 in Mechanics.   This included momentum and impulse, conservation of linear momentum and center of mass.

Areas that went well for me were momentum and impulse and conservation of linear momentum.  What helped me to really understand these two topics were first understand the graphs that went along with them.  This included Force vs. Time graphs showing the impulse to be the area under it.  These graphs gave me a better understanding of what I was solving for when I got to problems.

Center of mass was the topic I had the most difficulty with.  However plotting the points on a graph helped me with this as well.  The equation Xcm= (m1x1+m2x2).../m1+m2... really helped me understand finding the center of mass of different points.  Finding it for other objects such as rods however was still quite challenging.

My major key to success this week was working more with graphs.  Once I understood graphs whether it be just plotting point or graphs such as Force vs. Time, they all helped me get a better understanding of the topic I was working on.

## Astroids

Throughout my life I have heard many rumors of asteroids hitting earth or the moon but I've always wondered what kind of damage an asteroid could really cause.  The size of the explosion would be most impacted by the kinetic energy of the object that caused it.  This would mean that the mass and the velocity of the asteroid would be the main factors in the damage.  The average speed for asteroids approach either the earth or the moon is around 17km/hr.  Now that we have the speed, how can we find the mass of an asteroid traveling that fast through outer space?  Mass is calculated through the density and diameter of the asteroid.  The typical diameter for these objects are around a few hundred miles and the densities range for 3-8g/cm^3.  We can then find the kinetic energy and the angle at which the asteroid will strike the surface to determine how much damage any given asteroid will cause.

## Firearms

When put into its simplest terms, guns are not very complex machines.  The goal is to deliver the maximum destructive energy with the minimum amount of energy to go to the shooter.  Better more expensive guns will do a better job at accomplishing this task.  However, conservation of momentum is true in guns as well.   That means that the momentum delivered to the target still has to be equal to the momentum felt by the shooter.  This is felt through the recoil of the gun.  That is why bigger more powerful guns will have a bigger kickback on the person shooting it.  The goal of a firearm is also to use energy efficiently and that is dependent on  its construction.  The two main factors to this energy efficiency are the caliber of the gun and it's barrel length.

## Clouds

The physics behind clouds can actually be a whole profession.  It turns out clouds are much more complicated then most people may think.  At the base of it, clouds are made up of microscopic water droplets and or tiny crystals of ice.  These droplets are initially formed from condensation onto the nuclei then the air is supersaturated.  This happens when the air exceeds a critical value of condensation known as the Kohler Theory.  These condensation nuclei are a big part and are necessary for cloud droplets to form.   In warm clouds, larger cloud droplets fall at a higher terminal velocity; because at a given velocity, the drag force per unit of droplet weight on smaller droplets is larger than on large droplets.

## Popcorn

Popcorn has lots of physics behind the little pop.  Until recently, popcorn had only been studied for it's chemical properties and never the physics behind why it pops the way it does.  It comes from the fact that their is water in the kernel.  When it is heated above 100 degrees Celsius, the water turns to steam and expands inside the kernel.  It continues to expand until the shell can no longer support the pressure and it eventually pops.  As soon as it pops, the starch cools it down and ultimately turns it into the white flake of popcorn.

## Mafia 3

Mafia 3 is a new open world game on the market and is featuring some pretty cool physics.  One of the main focuses for the developers was the driving.  It is crazy to see how far video games have come and Mafia 3's driving is a great example of that.  The game takes crashes into account when the player is controlling the car.  Crashes now have a big affect on the handling of cars.  The game also offers two modes of driving, arcade and simulation.  Arcade is similar to most video games in which driving is very easy and unrealistic.  Simulation however is basically a driving simulation in which players will struggle to keep control over their car.  On top of all of this their are four camera options when driving to make it look much better from which ever angle you choose.

## Physics of bball

Marcus has been wondering why I always win in our 1 v 1 basketball games and their is lots of physics behind it.  The first part of my success is how high I am able to jump.  There are horizontal and vertical components to jumps and being able to shoot and or block shots during the top part of the flight plays a major role in winning.  I also am able to jump higher giving me the ability to have a longer hang time.  This increases the time during the top part of my flight.  The equation to calculate my time during the top period of the flight is d = V1t — 0.5g(t)2

## Waves

Waves have a surprising amount of physics behind them, and not the waves at football games.  The simplest definition of wave motion is that it moves energy from one point to another.  Waves are an oscillation of energy that travels through a medium.  Their are tow main types of waves, one being mechanical waves.  Mechanical waves travel through a medium and are then restored by restoring forces to reverse the work done.  The other type of waves is electromagnetic waves in which the main difference is that they do not require a medium.  They consist of periodic oscillations of electrical and magnetic fields generated by charged particles,

## Javelin Throwing

Javelin throwing as it can be implied is largely dependent on the throwing angle.  While it seems as if it should be like any other activity where 45 degrees is the optimal firing angle, it is not that case.  Wind speed and direction have a huge dependence on choosing this angle.  The strength and speed that the thrower can release with is also a huge factor.  When studied it was found that some of the best javelin throwers in the world were actually releasing at a angle lower than 45.  The optimal angle with average strength and wind speed factored in came out to be around 30 degrees.  At this angle the thrower is able to hold onto the javelin for a longer period of time than at a higher angle and that gives them the ability to generate a much higer initial velocity.

## Week 2

This week I studied chapter 4 which included work, energy and conservative forces, conservation of energy, and power.  I found however that I spent the most time learning and working on conservation of energy.

Areas that went well for me included work and power.  Work was mainly review and it was good to go back and solidify my knowledge on the topic.  This was the same for power as I found I didn’t take many notes.  Most of it was review and the questions seemed fairly straight forward.

The topics that were more challenging was energy and conservative forces and conservation of energy.  What I struggled with at first was the ability to start a question.  I was struggling to understand how the energy of a system was being affected and putting it into an equation.  However, once I practiced that more and more and was able to do it, the rest of the question came very easy.  I would then just substitute in the formulas and would continue with the question.

My keys to success are very similar to last weeks as I followed my own keys to success and found they worked very well.  I paused a lot more during videos to make sure I was keeping up and understanding every that was happening.  I also answered the examples on my own first and then would either compare my answer or get help if I was stuck.

## 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.

## Physics of Karate

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.

## Dimpled Golf Balls

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.

## Bulletproof Vests

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.

## Physics of a Frisbee

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.

## Water bottle flip

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.

## Physics of a yo-yo

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.

## Physics of sleeping

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!

## Physics of battlefield 1

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.

## Physics of a hot air balloon

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.

## Physics of a pushup

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.

## 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.

## 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.

## 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.

## Physics of motorized bikes

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.

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