Net Force Sample Problem Walkthrough

Suppose the tank below has just fired a projectile. Assume that the tank stays stationary during the whole process (besides the obvious barrel movement due to the recoil. Disregard that).

Please click on the two images below and follow the walkthrough and then ask me any questions you still have about using Newtons second law, F=ma.

What questions do you have? What was confusing about this problem? What emotion card would you hold up if we were in class and you just saw this walkthrough?

Speed of Light

On Thursday, September 22, 2011, it was reported that European researchers had detected neutrinos traveling faster than light. If this discovery proves to be valid and true, then this is an amazing milestone in physics.

The speed of light is approximately 186,282 miles per second and is said to be the fastest speed that any particle in the universe can travel. I think all of you should take a look at the article posted below and give your opinions on whether you think anything is faster than the speed of light.

http://news.yahoo.com/faster-light-discovery-raises-prospect-time-travel-204403395.html

Hope you enjoy,

Walter Hill

Hey Everyone
As we all eat good food and watch a great Monday Night Football game, shouldn't we know how physics plays a roll in football. Here is a ESPN sports science clip with one of the best QBs in the league, Drew Brees. Everyone comment and let us know who your favorite NFL team is. Some trash talking allowed!


http://www.youtube.com/watch?v=c6EguTZFK5s

Phil and I am a Eagles Fan

Awesome Projectile Motion Video!!!

Below you'll find a video showing a tank doing some target practice. It's awesome because you get to see it in a bunch of different angles and in slow motion!

Alrighty, all you aspiring engineers, this one's for you (although if a Chemistry major or NROTC student could solve this I'd be really impressed!).

So, let's say you knew that the tank stood 500 meters from the target. The tank and the target are on the same ground level vertically, but the barrel of the gun on the tank is 2 meters off the ground. It takes 3 seconds total for the target to be hit. Suppose that the barrel of the gun was angled at 30 degrees (theta = 30) with respect to the (+) x-axis.

WHAT IS THE INITIAL VELOCITY OF THE PROJECTILE?

By the way, this is a classic problem you would find in Dr. Sayar's Dynamics class!

BONUS:

YOU'LL NOTE THAT THE ABOVE PROBLEM WAS TOO EASY BECAUSE I GAVE YOU SO MUCH INFORMATION. NOW, I'LL AWARD A CANDY BAR OF YOUR CHOICE TO THE PERSON WHO CAN FIND INITIAL VELOCITY WITHOUT KNOWING THE ANGLE OF THE BARREL (THETA = ???) . YOU'LL HAVE TO USE 2 EQUATIONS TO FIND THE TWO UNKNOWNS. ALL YOU ENGINEERS SHOULD DO THIS SINCE YOU'LL HAVE TO DO IT EVENTUALLY IN DYNAMICS!!!

Trajectory with drag

I mentioned today in class that Halliday, Resnick, & Walker's diagram of a projectile trajectory under the influence of air drag was mistaken. I've created an Excel spreadsheet (just click on "File" and then "Download" to view on your computer) that illustrates what I meant. As you can see from the graph in the Excel spreadsheet, also shown here...

...a major difference that drag imparts is that the trajectory is not symmetric across the maximum!

Try changing the input values in Row 2 of the spreadsheet. How does a change in each input value impact the shape of the trajectory?

If you're really feeling adventurous, take a look at the formulas that are set up to calculate the motion! How does it work?

Brain Surgey, No Big Deal

Deep Brain Stimulation
Deep brain stimulation also called (DBS) is a way for people with a movement disorder to decrease as much undesired movements as possible. DBS was approved by the FDA in 1997 for tremors, in 2002 it was made available for patients with Parkinson’s disease, and in 2003 the treatment was expanded to people with dystonia and other movement disorders. Since this is a pretty new practice of medicine, the results of patients are measured and are used to further advance this practice. DBS helps these movement disorders by sending electric stimulating pulses deep into to brain, helping to control the stimulations that travel through the brain to the rest of the body, which controls every movement a person makes.
Deep brain stimulation is usually done in two separate surgical procedures. In the first of these, the patient is totally wake and responsive. During this surgery, the patient is given local anaesthesia to numb the head. A halo is screwed into the patient’s head. This metal ring is then screwed to the OR chair. This prevents the patient’s head from moving in anyway. The basics of this surgery is to first drill a hole into the patient’s skull and then insert the stimulating lead down into the patient’s brain. The surgeons have to determine the best place the insert the lead into the brain. A MRI helps locate and map out, the best possible angle for the lead to be inserted into the patient’s brain. While in surgery the surgeon finds the best depth for the lead and screws the electrode in place and tucks the extra wire between the patient’s skull and scalp. The doctors turn on the stimulator to make sure they receive a response from the patient, letting them know they have everything perfect. If everything in the surgery goes correctly, the patient will be released from the hospital the morning after the surgery. The patient is monitored overnight to make sure there are no neurological problems related to the surgery.
The second surgery is much less dangerous and is done in an outpatient procedure. The surgeon has the patient put under general anaesthesia, so the patient is asleep for the length of the surgery. The doctor next takes the wire connected to the electrode and runs it behind the patients ear and down behind the collarbone. There is a battery that is connected to the wire and it is placed under the collarbone. The battery is what sends the electric pulse to the brain. In recovery the doctor sets the device to low settings so the voltage is pretty minimum.
One battery and one electrode only affect one side of the body because the two different sides of our brain each control the opposite side of our body. So if the electrode is planted in the right side of a patient’s brain, the left side of the body is affected by the stimulation. The technique for the timing of when to do these surgeries varies between doctors and patient. Doctors can implant two electrodes, one on each side of the brain, at once and then put in both batteries a week or two later or they can decide to see if they get any benefit from one side before they do the opposite side at a later date. Doing the surgeries one at a time lowers the risks of complications with the surgeries. Then the batteries would also have to be put into the patient’s body on two different dates.
After a week or so of having the battery tied in with the electrode, the patient returns to the doctor to receive programming. This programming is done to find the best setting for the patient. The settings of the stimulator can be changed and adjusted with a wireless external controller. The doctor can change the voltage amplitude, the frequency and pulse width of the stimulator. The stimulator on each electrode has four different contact points where the stimulation can be sent to. The stimulator can be set either to a single contact point or to two contact points. When the current is sent to dual contact points one sends out a positive stimulation and the other sends out a negative pulse. This makes the pulse half way between both contact points because the positive and negative pulse attract. Several programming sessions are needed to optimize therapy for each patient and may take up to six months to finalize the programming settings. Over time, as the disease progresses, the stimulation continues to control tremor, stiffness and slowness. After the programmer finds the best settings for a patient the only further medical treatment is the replacement of the battery. Depending on the settings of the stimulator the battery life is between 2-5 years.
There are some complications and risks with going in to the brain surgery. One of the biggest worries for this surgery is the risk of a patient’s speech getting worse, which is about a 3% risk. Another risk is infection which most likely would require the removal of the DBS hardware and another surgery. As with any of the best technology mankind comes up with, the hardware can stop working correctly. The electrode can get dislodged and move. These risks are very rare and with the benefits high, most patient’s trust in the doctors to give them a better life. As with most medical procedures younger patient have a lower risk of complications then older patients
Most patients see some difference in their movement ability immediately. Patients with Parkinsonism can expect a great, positive, change in movement control immediately. People with dystonia and other movement disorders may not see immediate or drastic results. With dystonia there is a much slower progression of improvement to movement control and with time DBS can extremely helpful for every move a patient makes. DBS surgeries also are starting to be found beneficial to people who have OCD and other mental disorders.

Physics in Movies

Physics is used in many popular movies today. Iron Man, Fast & Furious, and Transformers are a few top box office movies that utilize physics concepts.

Iron Man uses physics when Tony Stark, the creator of the Iron Man suit, creates an arc reactor to go inside his chest to survive a chest injury. In this movie the arc reactor was a energy source and used electromagnets.

The Fast & Furious series of movies explores the relationship between physics and street cars. The characters in the movies modify engines to achieve maximum speeds, and explore the concepts of force, motion, and electrical systems.

The Transformers movies also relate physics to the real world. The uses of weaponry and fast cars in the movie both relate to physics.

My challenge to you is to think of some of your favorite movies and how they may use physics concepts. I am very interested to see your responses!

Walter Hill

Gravity's effects on chemical reactions

Kyle Bosanko posed a GREAT question on my article last week about mapping out g on the moon. (My only regret is that I didn't get around to reading it until today! Sorry!) Here's Kyle's question:

I just finished up some chemistry homework and was wondering how much gravity [a]ffects chemical reactions. Would a reaction differ it were on the moon. I am particularly interested in reaction rates.

I'm not as familiar with gravity's impact on chemical reactions (though I suspect it's minimal), but I DO have a neat simulation to show you about a similar problem!

Click to Run

This simulation (Just click it to run!) shows the behavior of an ideal gas, which is where gas particles roam freely until they bump into each other or the walls of the container. There's a slider that will allow you to adjust the strength of "gravity" (really, our g) to see what effects different levels of gravity have on the gas's behavior!

Enjoy!

D-Day and Turning Tides

Who likes to fish? Do all you fishers know about tides? When's the best time to fish, high tide or low tide? Knowing how the tides rise and fall is important to a fisherman. There are numerous Physics concepts behind why and how tides work. Gravity and the centrifugal force are just two of these key concepts.



You may be surprised to know that tides also played a key role in the World War II D-Day invasion. German leaders suspected an American invasion long before it happened. They knew it would be an invasion by sea, and they even suspected that the invasion would come during high tide. At Normandy, when the tides were low, German commanders caused millions of obstacles to be erected in the sand in preparation for the Allied attack. They stood at the ready to beat back the American surge.



Why would German commanders have anticipated an American invasion at high tide as opposed to low tide? Why would they have built all the obstacles?

Don't know? Read the whole fascinating tale at http://dx.doi.org/10.1063/PT.3.1257 .

BONUS:
A FULL SIZED CANDY BAR OR SIMILARLY-PRICED TREAT OF CHOICE WILL BE AWARDED TO THE FIRST PERSON TO POST A COMMENT EXPLAINING, ACCORDING TO THE ARTICLE, HOW GRAVITY AND THE CENTRIFUGAL FORCE INTERACT TO CAUSE HIGH AND LOW TIDES.

Hi Guys

Next week I will be coming to your class and showing a presentation on how physics apply in a car crash.

Here is a video about the new smart cars and how safe they are. It is shocking how safe they where able to make such a small car.

http://youtu.be/ju6t-yyoU8s

I want you guys to tell me about your experiences, either in a car crash or witnessing an accident.

Thanks guys

Phil

Warm-up Assignment #6 responses

I’ve finished reading your great questions on Warm-up Assignment #6. I apologize it took me so long to process them, but I think you’ll find the discussion worth the wait! Below, I’m pasting in anonymous responses that I received, followed by my commentary for each.

“I'm currently taking Calculus 2, so my question for you is are we going to be using derivatives and integration alot during physics? I'm pretty good with derivatives but I'm not that strong yet with integration.”

A great question, especially since we haven’t done too much calculus yet!

PHYS 151 assumes that you’re in Calculus II right now. That means our textbook and assignment problems assume that they can throw derivatives your way without having to give you a refresher. (That may be a bad assumption, so see the links in response to the student quote below!) The textbook uses a lot of derivatives in its mathematical manipulations—for example, in turning Delta x / Delta t (the average velocity) into dx/dt (the instantaneous velocity). The problems will use derivatives in a more subtle manner. For example, a number of problems are going to ask you for “the least amount of force necessary” to accomplish some goal. When you see “least,” you should think “minimum,” which should lead you to a first (and likely second) derivative test to find the minimum. (What should you be differentiating with respect to? That depends on the problem…)

The assumption that you’re in Calculus II right now also means we’re not doing integrals—yet. We’ll first introduce integrals in our unit on energy (coming in October), which gives you lots of time to solidify your understanding of integrals.

PHYS 152, on the other hand, will use integrals a lot!

“I'm a little foggy when it comes to all the rules of derivatives.”

Aren’t we all! I’ve found a number of helpful resources at

http://www.mathwords.com/d/derivative_rules.htm (see also the links at the bottom of this page)

http://en.wikipedia.org/wiki/Differentiation_rules (contains some good explanations; be sure it matches what you know, though, as Wikipedia can be edited by anyone!)

http://math.arizona.edu/~calc/Rules.pdf (short and sweet!)

http://www.math.brown.edu/help/derivrules.html  (contains interactive sample problems and explanations; click on the “+” buttons to view the hidden information)

The rules that I see students missing the most are the product rule (some of you missed this in the damped harmonic motion functions in the most recent Graphing Project) and the chain rule (just keep taking derivatives until you multiply by dt/dt).

“I dont have any misunderstandings, just still trying to adapt to physics and what each means, like velocity is position over time and so and so forth. I am very new in this material and trying to kick my butt to do good in this course.”

That is a difficult transition to make! There are lots of study techniques you can use to help you internalize the meanings of physical properties. Some students keep a running equation list of the most important equations in the textbook so that they can view the most important concepts at a glance. Other students like to transcribe their notes to another notebook or electronic file after each class meeting to make their notes more organized and to reinforce the material in their minds. Many students also find it helpful to form an out-of-class study group with classmates to meet weekly over pizza/coffee/ice cream/a favorite TV show to work problems, check each other’s work, and ask each other questions.

Announcement

For those of you that are interested in engineering, there is an NSPE (National Society of Professsional Engineers)/ FES (Florida Engineering Society) meeting on Wednesday, September 14 at 12 pm in Nelms 1.

Mapping g on the moon

http://www.npr.org/2011/09/10/140361610/nasa-launches-probes-to-study-moon describes a recently launched unmanned NASA mission to the moon to map out the moon's gravitational field. What is the gravitational field? It's quite simply the acceleration due to gravity ("g" as we've been calling it in class) as a function of position around the moon!

On the surface of the earth, g is a pretty consistent 9.8 m/s^2, but it does vary depending on your position on the planet, since Earth is not a perfect sphere. And once you start to get out into space, g begins to diminish drastically, dropping off like 1/r^2, where r is the distance between you and the center of the earth!

The moon's acceleration due to gravity behaves much the same way. On the surface of the moon (at least the parts we've been to!), it's about 1/6 of our g on earth (so about 1.7 m/s^2, give or take), and also drops off like 1/r^2 (where r is the distance between you and the center of the moon) as you leave the surface.

These probes will measure these variations in the moon's g as they orbit on opposite sides of the moon! By the way, the GRACE mission (http://www.csr.utexas.edu/grace/) did the same thing on earth! Here's a map of the results, depicting the difference between the local g and the average g: http://www.csr.utexas.edu/grace/gallery/gravity/03_07_GRACE.html, where the red regions represent a higher value of g and the blue regions represent a lower value of g (measured in units of "milligals," which are named after Galileo; 1 gal = 1 cm/s^2).

High Speed Railways

Here is a physics research paper i wrote on High Speed Railways (bullet trains). Take a look at this paper for background information because I will be making a presentation to your class on bullet trains on Friday, September 16.

-Walter Hill

High Speed Railways

High Speed Railways (HSR), better known as “bullet trains,” have revolutionized transportation over the past half century. They use innovative technology ranging from electromagnetic devices to linear motors to allow passengers and cargo to travel efficiently and safely at high speeds. These bullet trains are being improved using Magnetic Levitation technology and propulsion systems to enhance their productivity and capabilities.

The bullet train was born in Japan in October of 1964 with the Shinkansen. The first train the Tokaido Shinkansen ran about 320 miles from Tokyo to Osaka. The early bullet trains ran with speeds up to 125 miles per hour (mph) (Railway-Technology). Since the Shinkansen bullet train, technology has improved to allow for higher speeds and to travel longer distances. Today, in Japan bullet trains run over 160 mph, over 200 mph in China, and are used to carry mail in France. HSR are also used for various purposes in the United States of America, mainly in Northeast cities like Baltimore, Washington DC, New York, and Philadelphia. HSR also offer many advantages over automobiles and airplanes. Bullet trains can carry more passengers than both modes of transportation and travel at faster speeds, and are more environmentally friendly. According to an article in the New York Times, HSR leave a significantly smaller carbon footprint than airplanes and automobiles (Glaeser).

The bullet train has an effective design to allow for the travel of long distances at high speeds. To be aerodynamic and minimize wind resistance, the bullet trains use a streamlined body design to allow travel at high speeds. The front cars of bullet trains resemble power noses similar to the nose of airplanes because they are extremely aerodynamic. The front car of the bullet train feature dome canopies that allow drivers extended forward vision. Bullet trains also have specialized technologies that allow passengers to have comfortable transportation. The cars of bullet trains sit on top of flatcars that use air springs to compress air and absorb wheel vibrations from the track. This technology does not allow wheel vibrations from the track to reach passenger and cargo cars. The cars on the bullet train are also soundproof so passengers will not hear track vibrations and wind resistance. (Web Japan).

To ensure safety on HSR, railways are carefully designed and have technology to allow travel at safe speeds. The railways of HSR are made of steel that are mounted on concrete blocks. Bullet trains use wide gauge tracks and do not feature any sharp curves for high speeds and maximum carrying capacity. The speeds of bullet trains are controlled by Automatic Train Control (ATC). ATC transmits information about speed from the railway to the driver to maintain travel at designated speeds. To prevent congestion and control HSR traffic Centralized Traffic Control (CTC) is used. CTC manages the time and distance between trains for safety. Another safety precaution that allows safe and smooth travel is that trains never cross tracks at the same level. (Web Japan).

To improve bullet trains in the future, Magnetic Levitation (Maglev) technology is being tested. Maglev uses electromagnetic fields to levitate, suspend, non-contacting vehicles. Two options for Maglev are electromagnetic suspension (EMS) and electrodynamics suspension (EDS). Major advances in electronic control systems have paved the way for EMS. It is an attractive force levitation system where electromagnets on the bullet train would interact with the railway. EMS will maintain air gaps between the train and railway preventing unwanted contact between them. The changing magnetic fields created by EMS will compensate for errors in air gaps caused by differences between weights on the bullet train and the railway. EDS is a repulsive force levitation system that would use magnets on the moving train to induce currents on the railway. The repulsive forces produced by currents would create stable vehicle support because of increased magnetic repulsion forces as the air gap decreases. The only complication with EDS is that its repulsive magnetic forces would not work until the bullet train is in motion. EDS has progressed because of advances in cryogenics and magnet technology. (Ferguson).

Advancements in linear motors are another future improvement for bullet trains. Today linear synchronous motor (LSM) and linear induction motor (LIM) are being tested as future propulsion systems for bullet trains. LSM, also known as “long stator” propulsion, uses winding on the railway to attain high speeds. LIM, “short stator” propulsion, uses onboard winding. While LSM is faster than LIM it is more expensive because of the construction needed with the system. On the other hand LIM would generate less revenue because of higher operating costs. Other alternatives motors in the works are a gas turbine or turboprop systems. (Ferguson).

High speed railways are an innovative and interesting mode of transportation. Their unique design makes them a safe, efficient, and fast. They are also more economically and environmentally friendly than automobiles and airplanes. With future improvements coming for their motors and the Maglev technology, bullet trains could soon become the most reliable transportation available around the world.

Works Cited

Ferguson, L Joe. "Maglev Technology." The Enterprise Center. 30 March 2011. http://www.theenterprisectr.org/high-speed-ground-transportation/maglev-technology.html.

Glaeser, Edward L. "How Big Are the Environmental Benefits of High-Speed Rail?" 12 August 2009. New York Times. 25 March 2011. http://economix.blogs.nytimes.com/2009/08/12/how-big-are-the-environmental-benefits-of-high-speed-rail.

"Shinkansen High-Speed 'Bullet Train'." Railway-Technology. 4 April 2011. http://www.railway-technology.com/projects/shinkansen.

"Train Technologies." Hi Tech Bullet Train. 31 March 2011.

http://web-japan.org/kidsweb/hitech/shinkansen/shinkansen02.html.

Solution to Avg Velocity Prob

Below you'll find the solution to last week's sample problem. I hope many of you attemtped and completed the problem on your own.

If you had trouble with this problem, please go through this step by step solution to enhance your understanding. It is VERY IMPORTANT for this course and for your life that you understand how to harvest information out of a paragraph of text and manipulate what is given in order to find the answer that is called for.

Kudos to Elemon who was the only person to submit a correct response before the deadline. Good luck on your coursework in the coming week!

The Dames Point Bridge

You may not realize but the longest cable suspension bridge in the United States is just miles away from our JU campus. This bridge is right over two miles long, going over the Saint Johns

River. The central span of the bridge deck between the two tower is 471 feet above the water. These towers go 80 ft below the water's surface to make sure the bridge has a steady foundation. The steel cables are sheathed within a steal pile. The cable starts at 65 feet long and at the highest point the cables are 720 ft long, totalling into 21 miles of steal cable. This bridge is most noticable because of how steep it takes you, over 40 stories high in one horizontal mile. It is definitely one of the prettiest and scariest bridges that I have seen, I personally always have a fear of bridges. This is the big challenge for the designers of bridges. Not only do they have to design the bridge sturdy and safe but the city wants a structure that adds beauty to their skyline.

What are some beautiful bridges you have seen in your life and what in paticular makes them pleasing to you?

Phil

Nuclear Energy

Nuclear power uses nuclear fission and fusion to generate power. It accounts for about 15% of the world’s power and is relatively safe. Nuclear propulsion is used on Navy submarines and aircraft carriers. Nuclear energy can also be used in weapons, which are very dangerous and has lasting effects on areas affected. The most famous example of nuclear warfare is when the US dropped an atomic bomb on Hiroshima during World War II. In all, nuclear energy is a source of energy for the future and has many uses.

Here is a link if you want more information on nuclear energy:http://library.thinkquest.org/3471/nuclear_energy.html

For those of you that are interested, below is a link to US Navy website. It lists many jobs that are associated with nuclear physics. This is a very good paying job opportunity after college and can also earn you money while in college.

US Navy careers with nuclear physics: http://www.navy.com/careers/nuclear-energy.html

Also attached is a poster for the Naval Nuclear Propulsion program:

Walter Hill

Week 2 In-Class Problem picture

I brought my camera to class today, but was engrossed with all your wonderful calculus, I forgot to take any pictures of your work!

Here is the one picture I did get, from Semira, VonHayes, and Antonella's group. Much appreciated. :-)

Sample Problem: Average Velocity

One of the most challenging parts of Physics is the story problems! These problems force you to take a paragraph of written information and convert it into a math problem, with all the information properly inserted into the appropriate formula. So here is a problem to give you some practice at developing that very important skill. It is a fairly simple problem. The challenge is to get it into a simple form.

To make this challenge a bit more appealing, I am offering a full size candy bar to anyone who properly sets up the problem and comes out with the right answer. I want you to show all your work.

You have until next Wednesday to answer the problem for the candy bar. You can hand me your worked out solution in class on either Monday or Wednesday. Next Friday I will post a worked out solution. Good luck!

PROBLEM
A Navy battleship embarks from the Naval station in Mayport on its way to Afghanistan to shore up defenses there. Assume that its destination is 5000 kilometers away. Assume that the ship left harbor at 9am on August 25, 2011, and arrived at its destination this morning, September 2, 2011 at 9am. What was the ships average velocity during the voyage? Give your answer in miles/hour.