The Physics of Rugby

 As a rugby player, I have been really curious as to how physics relates to passing and kicking during the game. After taking physics 111, it seems that kinematics and forces can be used to explain the motion of the rugby ball during a pass and a kick, as well as the motion of players during a scrum and tackle. During passing, the key is to get the ball to your teammate as fast and as straight as possible. 

Newton’s First Law of Motion states that an object at rest will remain at rest and that an object in motion will stay in motion unless acted upon by an unbalanced force. Newton’s First Law of Motion is seen in Rugby when a player kicks the ball. Before a player kicks the ball, the ball is at rest and will remain like so until an unbalanced force (the players foot) acts on it. Once the ball is kicked, it will go up into the air until an unbalanced force acts upon it, which in this case is the force of gravity which will cause the ball to come back to the ground. The horizontal speed of the ball will remain constant as only gravity acts constantly upon the ball (assuming air resistance is negligible), but the vertical velocity will change. Additionally, forces are involved when a player catches the ball. When a ball is kicked and a player is in position to catch the ball, they will apply a force that is equal and opposite to the ball. Lastly, Newton’s First Law can be used to explain the forces that occur during a scrum (see above photo for reference of a scrum). During a scrum, two sets of players will push against each other usually with the same amount of force. Thus, the scrum would not be moving and would be at rest. The scrum will remain at rest until one side of the scrum pushes the other players with a greater amount of force to push the other team backwards. 

Newton’s Second Law of Motion is also seen in rugby when a player tackles an opponent. Newton’s Second Law of Motion states that force is equal to the mass times the acceleration. Thus, when a player runs towards an opponent, they have a certain mass times acceleration (F=ma). This means that the larger the player’s mass is, the larger the force they will have. If a player has a greater force as a result of their large mass, they will be able to hit their opponent with greater force and will be able to tackle their opponent. Additionally, the faster the player’s acceleration, the larger the force they have. Thus, it is important to be both heavy and fast in rugby if you want to make good tackles. 

 

References:

https://pdfs.semanticscholar.org/204d/e75fab5746a27948662c6274b7afdc67865e.pdf

 

Dr. Erin Kara

 

     Erin A. Kara is an assistant professor of physics teaching in the department of physics at MIT. Professor Kara has been teaching at MIT since July, 2019. Erin Kara earned her B.A. in physics with a minor in art history at Barnard College in NYC. After obtaining her B.A in 2011, Professor Kara traveled to the UK and obtained her master’s and a PhD at the Institute of Astronomy at the University of Cambridge. Fascinatingly, Professor Kara also had the opportunity to conduct a fellowship at NASA’s Goddard Space Flight Center! Professor Kara is an accomplished physicist, obtaining the Murdin Prize for best graduate student paper at the University of Cambridge (2013), and the Postdoctoral Scientist Prize for Excellence at University of Maryland’s’ department of Astronomy. Additionally, in the short time Ms. Kara has been a professor, she has already contributed significantly to the field of astrophysics, with five different publications.  

            As an observational astrophysicist, Professor Kara’s research primarily focuses on supermassive black holes and X-ray reverberation mapping. In fact, Professor Kara herself progressed this new X-ray reverberation mapping technique. This new technique allows astronomers the ability to map the gas that falls onto black holes so they can measure how curved spacetime is affected. In her most recent research paper, “The corona contracts in a black-hole transient” (2019), Professor Kara explores X-ray observations of the transient black-hole (MAXIJ1820+070). Interestingly, the results of the paper show that the time lag reverberations between corona and the irradiated accretion disk are 6-20 times shorter than had been previously determined. 

 

References:

https://web.mit.edu/physics/people/faculty/kara_erin.html

https://www.nature.com/articles/s41586-018-0803-x

 

The Physics of The Biles

    Simone Biles is an incredible gymnast, who continues to shock the world with her ability to seemingly defy the laws of physics! I have always been fascinated by the world of gymnastics and how they are able to do such incredible movements with their bodies. Thus, when I was looking to investigate some physics phenomenon I was immediately drawn to gymnastics. When beginning to look into this I noticed a movement that seemed to draw on multiple concepts of the physics we have discussed this semester, a movement named after no other than Simone Biles. The Biles is a double half-layout with a half twist and a blind landing. This move is so shocking because at first glance it appears that Biles is actually gaining angular momentum, which we know is impossible because of the Law of Conservation of Momentum. In this movement she flips twice and then still has enough momentum to complete a turn and land facing the way she was running. In this movement, Biles utilizes everything from torque, to momentum, to kinetic energy and moment of inertia. Thus, I decided to look over the physics of this motion with the help of Sheffield Hallam University’s John Kelley and Cairan McInerney who analyzed Biles movement in 2016 after she successfully performed the move in an international event. 

     The first part to think about in this move is the idea of angular momentum, which is angular velocity times the moment of inertia. Thinking about this expression we known that the momentum must be conserved throughout the movement, thus if Biles wants to complete two flips with the same momentum she must theoretically increase her angular velocity in order to spin faster. Yet, spinning faster means she would need to decrease her moment of inertia in order to conserve momentum. In order to do this, similar to the ice skater problem we did in class she would need to decrease her radius. She does this by creating an arch in her body, decreasing her radius in the y-direction, as well as bringing her arms to her hips, which decreases her radius in the x-direction. 

 

    Another interesting thing to look at in this problem is looking at her energy.  On the floor gymnast are able to build up energy by running diagonally such that they can turn their horizontal kinetic energy into vertical and rotational energy. However, the sprung floor also plays a critical role in how gymnasts are able to utilize physics as because of Newton’s 3^rdLaw, which states that two objects will exert equal and opposite forces onto each other. This is because as the gymnast applies a force, by doing a cartwheel or flip, the sprung floor will provide, and equal and opposite force back up on the gymnast by over a greater duration of time. Thus, the gymnast’s force as well as the spring force will be store then released onto the gymnast to allow her to complete such incredible motions.

 

    In the article that I read, John Kelley and Cairan McInerney, also look at the amount of energy and force that Biles needs to exert in order to complete the movement and while the math and process is a little to long for this blog post the results are incredible. The ability to calculate these things provide Biles and trainers with valuable information about how she must execute the move in order to succeed. As I talk about in my other posts this is the work of sports engineers who use the power and understanding of physics and apply it to performance. This work continues to amaze and fascinate me and I hope to see more defying of physics by the Women’s US Gymnastics team in the upcoming Olympics! 

Works Cited: 

https://www.inverse.com/article/19429-2016-rio-olympics-simone-biles-gymnastics-physics-medal

https://plus.maths.org/content/simone-biles

Professor Steve Haake- Sports Engineering

     Steve Haake is a Professor of Sports Engineering and the Director of Engagement at the Advanced Wellbeing Research Centre at Sheffield Hallam University (Sheffield Hallam University). Professor Haake has his undergraduate degree in physics from the University of Leeds and a PhD from the University of Aston, where he was sponsored by the Royal and Ancient Golf Club of St. Andrew for his work on golf balls on golf greens (Durrani). Haake found an interest in combining his knowledge of scientific mechanisms with his passion for sports and found that it was widely appreciated by the sports community. Haake works as both a lecturer of mechanical engineering as well as the supervisor of a sports engineering research group that offers assistance to sporting associations worldwide. Haake also is the founder of the Advanced Wellbeing Research Centre at Sheffield Hallam which works to use sports mechanics as a way to help people become more active. Through his publications of books and multiple journal articles as well as his teaching and research Haake has made a name for himself at the forefront of the science of sports. By combining physics and engineering, Haake attempts to understand the mechanics of sports such that he can improve performance and efficiency. 

    Professor Haake has worked on numerous projects through his research group’s consulting program but one that I found extremely interesting was his work, A New Measure of Roughness for Defining the Aerodynamic Performance of Sports Balls.In this journal article Haake and his team discuss how the performance of balls, such as soccer, tennis, and golf, were determined by the roughness k/D. Yet, this measurement was unable to predict the ball’s change from laminar flow to turbulent flow. However, in this paper they hypothesize that through a new statical measurement, one commonly used in tribology, they were able to analyze the full aerodynamic motion of the three different types of balls. This paper has since then been cited in multiple other journal articles that look at contrast swinging in a cricket game or the first serve of a tennis ball. Thus, it is clear that Professor Haake’s work translates directly into the game itself as his analytic techniques and conclusion are used to enhance the play of so many athletes. Professor Haake represents the beginning of an interesting new subfield of science that directly connects performance and physics and engineering. His work is a testament to the interconnectivity of our world and physics! 

Works Cited: 

https://stevehaake.com/research/

https://journals.sagepub.com/doi/10.1243/0954406JMES414

https://www.shu.ac.uk/about-us/our-people/staff-profiles/steve-haake

Dr. Jennifer Dionne

 

    In a lab at Stanford University, Dr. Jennifer Dionne (left) and Loza Tadesse (right) are diligently studying how to use surface-enhanced Raman spectroscopy to identify bacteria in their natural habitat. Dr. Jennifer Dionne received her Ph.D. in Applied Physics at the California Institute of Technology and B.S. degrees in Physics and Systems & Electrical Engineering from Washington University in St. Louis. Her research focuses on developing nanophotonic methods to observe and control chemical and biological processes as they unfold with nanometer scale resolution. This year, she was promoted to Senior Associate Dean of Research for Platforms/Shared Facilities at Stanford. Loza Tadesse, one of Dr. Dionne's students, is a Ph.D. candidate in bioengineering. Before attending Stanford, Tadesse was a medical student at St. Paul Hospital Millennium Medical College in Ethiopia. 

   When using surface-enhanced Raman spectroscopy (SERS), researchers place a bacterium near a metallic surface. Then they shine a laser on the surface plasmons in the metal. The resonant interactions increase the Raman scattering from the bacterium’s cellular material. The boosted scattering signature allows the researchers to identify the bacterium and its molecular structure. This technique has been confirmed for dry samples, which requires the samples be prepared; however, bacterial cells live in water. Tadesse and Dr. Dionne, along with their colleagues, have developed a protocol for liquid SERS measurements. This may allow for real-time testing of the susceptibility of bacteria to various drug treatments. A technique such as this one could speed up the time it takes to create and perfect antibiotics.

https://physicstoday.scitation.org/do/10.1063/PT.6.1.20201002b/full/

https://profiles.stanford.edu/jennifer-dionne

https://profiles.stanford.edu/loza-tadesse

Barrel Racing with Newton

  Whenever I think of physics around me, I often think of horseback riding. I have grown up around horses and have spent many hours of my life riding. While I currently no longer compete, I still enjoy watching my friends compete in various areas of the sport whether it be show jumping, cross country, or even barrel racing. I have never competed in barrel racing, as I do not ride western, but one of my friends travels around the country (pre-covid) following the rodeo circuit and competing in barrel racing. 

    Barrel racing is one of the events seen at a rodeo. In this high speed event, a horse and rider attempt to run a cloverleaf pattern around barrels in the fastest time.  The video below shows Chayni Chamberlain, a 10 year old girl from Texas, competing with her horse. 

    All three of Newton's Laws of Motion are present when barrel racing. Newton's First Law of Motion is observed when the horse takes off out of the gate. When a horse moves forward, the rider is thrown backward slightly. Newton's First Law states that an object at rest will stay at rest unless acted upon by an outside force. In this case, the horse is an outside force to the human. If the rider does not continually adjust her balance to stay with the horse, she will be left behind. Newton's Second Law, F=ma, describes the effort needed to come to a stop. Heavier horses require more force to stop as do horses traveling at faster speeds. I find it remarkable how quickly horses can stop or change direction based on their size and speed. Newton's Third Law of Motion states that every action has an equal and opposite reaction. The horse exerts a force on the ground which exerts a force back on to horse. Additionally, as the rider sits in the saddle, she (and the saddle) exerts a force on the horse's back which exerts a force back on the rider. If the horse hits one of the barrels, it applies a force to the barrel that applies an equal and opposite force on the horse. 

    Other concepts in physics found in barrel racing include friction and centripetal force. Friction exists between the horse's hoofs and the sand. Without friction, the horse would slip and fall. Friction is also present between the rider and the saddle and between the rider's legs and the side of the horse. When the horse travels around the barrel, the centripetal force can be calculated by multiplying the horse's mass by its squared velocity and dividing it by the radius of the path. 

https://www.youtube.com/watch?v=WE4Nvvacbnw

Trampolines: Fun with Physics

 

Although trampolines appear as solely a fun activity, it is actually a complex system involving physics to allow this “fun” to happen. Bouncing on a trampoline perfectly demonstrates conservation of energy-  Kinetic and Potential energy. Additionally, motion on a trampoline is able to demonstrate all three Newtons Laws of Motion. 

In order to understand why we are able to bounce on a trampoline, we must first look at the Law of Conservation of Motion. Potential Energy (PE) and Kinetic Energy (KE) are what allow us to jump much higher on a trampoline, than we would on the ground- hence the “fun”.

Several equations that help to explain trampoline motion:

E = PE + KE + Q

PE = mgh

PE = ½ KX2 

KE = ½ mv2  

F = -kx (Hooks Law) 

Once an individual has “bounced” on the trampoline, much of the Potential energy store in the trampoline springs (PE = ½ KX2) is converted to Kinetic Energy (KE = ½ mv2).  This KE allows the individual to eventually reach a maximum height, at which then all KE is converted into gravitational potential energy  (PE = mgh), which is eventually converted back into PE of the trampoline springs. 

However, it is important to note that our ability to “bounce harder” aka reach a higher height is dependent on our ability to transfer maximal energy.  Should be obvious - spring specifications (the spring constant, spring length, and number of springs attached) largely impact the trampoline's ability to project an individual upwards. Additionally, it has been noted that an individuals’ strength (ability to produce maximal efficient force on the trampoline) has an effect on the “bounce” height. 

Diana Carver

 

Diana Carver, Ph.D., is currently an assistant professor of Radiology and Radiological Sciences at Vanderbilt University. Diana Carver has a lengthy history of Physics education in a variety of fields. She received a B.S from the University of Texas in Physics, Astronomy, and Geophysics. Then received; an M.S from the University of Arizona in Planetary Science, an M.S from Vanderbilt University School of Medicine in Diagnostic Medical Physics, and finally a Ph.D. from Vanderbilt University in Physics. Carver completed her dissertation in "Pediatric Red Marrow and Organ Radiation Dose Estimates in Computed Tomography from Monte Carlo Simulations". Lastly, she completed residency in Imaging Physics at The University of Texas MD Anderson Cancer Center. More recently, in 2017, she joined Vanderbilt University for Radiology and Radiological Sciences. Carver also is also board certified in Diagnostic Medical Physics by the American Board of Radiology. Carvers’s more recent publications involve quality control of radiography via use of medical physics. 

https://wag.app.vanderbilt.edu/PublicPage/Faculty/Details/42640

https://www.vumc.org/radiology/person/faculty/carvede1

Dr. Powtawche Valerino

Dr. Powtawche Valerino

Dr. Powtawche Valerino is a guidance engineer who works for Aerodyne Industries, an aerospace engineering and information technology services firm based in the NASA-Marshall Space Flight Center in Cape Canaveral, FL. Additionally, she works as a navigation engineer at NASA’s Jet Propulsion Laboratory. She obtained her undergraduate degree in mechanical engineering from Stanford University and both her masters and doctoral degrees in mechanical general engineering, with a concentration in aero-astronautics, from Rice University. 

She helps in planning and designing maneuvers for unmanned spacecraft missions that travel into deep space. She helps to determine whether specific changes need to be made or maneuvers performed to maintain the trajectory of the spacecraft. She is among a handful of scientists that helped to report on, and maintain, the Cassini Mission to Saturn well beyond its original timeline (was supposed to be 4 years but ended up lasting 17). Most recently, she worked on the Parker Solar Probe, the closest man-made spacecraft to ever approach the Sun. It is expected to get as close as 4 million miles (1/10th the distance between Mercury and the Sun) and is to analyze the outer atmosphere of the Sun and its contents. In total, after eventually using Venus as a speed brake, it will complete 24 revolutions around the Sun before the mission is set to end in 2025.

https://www.nasa.gov/feature/powtawche-valerino

https://www.linkedin.com/pulse/meet-powtawche-valerino-jpl-navigation-engineer-who-personifies-chen/

https://www.nytimes.com/2018/08/11/science/parker-solar-probe-launch.html

The physics of the rocket launch

With the recent revival in popularity of space travel and exploits, either planned or already achieved, space tourism has become a recent buzzword of newer pioneering space enterprises such as Virgin Galactic and SpaceX. The seeds of a nascent space tourism industry had already been planted but appear to have started growing thanks to the efforts of companies such as these. Over the past 15 years, prices for tickets on rocket launches have risen from around $250,000 to $55 million. Additionally, each night spent on the ISS during the trip would cost an additional $35,000 per astronaut. Despite all this, Virgin Galactic has received enough interest to begin launching flights in the very near future.

With all that, the question is presented: what are the physics behind launching into space?

The launch

The most important concepts describing rocket launches are momentum and impulse. When a rocket is launched, a chemical reaction occurs within its boosters that then produces a force that acts in the direction of the rocket’s nose cone. The rocket’s weight acts as a force in the opposite direction of the boosters’ exhaust fumes. 

This is a basic diagram showing the vectors involved in the launch: 

These equations best explain what is happening.

At the point before launch, the force of the launchpad (normal force) is equal to the force of the weight rocket (and their velocities are zero). Thus momentum is zero at the moment before launch. After the fuel is ignited and the exhaust gas pushes downward (force acts in +y direction because of Newton's third law of motion). This introduces a new constant force, creating an impulse and thus an imbalance in the conservation of momentum equation. In conserving momentum, the rocket must then increase in velocity in the opposite direction of the force (-y direction) because the momentum of the exhaust gases is extremely high. Despite fuel being burned and the mass of the rocket reducing with time, this change in mass does not fully account for the force of the exhaust gases after a certain time period of being applied constantly (which explains the brief period between ignition and launch). Thus, the rocket must accelerate until its momentum ‘catches up’ to the total impulse resulting from thrust (this generally only being achieved by the complete depletion of the fuel tanks)

https://www.cnn.com/videos/tech/2020/11/17/space-tourism-miles-obrien-anderson-cooper-acfc-vpx.cnn/video/playlists/anderson-cooper-full-circle/

https://www.bbc.com/news/business-50929064

The physics of pulling in a swimmer while white water rafting

 One of my family’s favorite things to do is go white water rafting. One of the most important things you need to know is how to pull someone back into the boat if they fall out. The technique that is used for this begins with dunking the swimmer under the water by their life jacket straps then leaning back onto the boat to pull them up on top of you. The physics concept this mechanism relies on is the buoyant force. When the swimmer is pushed all the way under the water, more volume is displaced which increases the buoyant force. Since the buoyant force can be written as Fb= ρfluidVg, the greater the volume displaced, so the more of the swimmer’s volume that is submerged, the greater the buoyant force is which allows for the rescuer to apply a smaller force and still pull the swimmer out of the water

The best thing about this technique is that it allows for smaller rescuers to pull up bigger swimmers. In this instance, if the swimmer starts at rest and ends at rest, we can approximate the amount of force a rescuer needs to exert to pull a swimmer up enough to pull them up out of the water. 

If this is the system:

The force the rescuer needs to apply is:

Once the swimmer has been pulled out of the water, the second part of the mechanism, where the rescuer leans back on the boat and rotates about their feet, pulls the swimmer over the horizontal distance of the tube on the boat. This portion of the mechanism relies on the torque the rescuer generated by rotating backward, pulling their center of mass from directly over their feet to a more horizontal position. Since the torque is not constant, the angular acceleration is not constant, and thus the amount of work done by the rescuer can be approximated by finding the area under the graph of the torque as the angle changes. 

In this portion of the mechanism, you can find what speed the rescuer and the swimmer hit the surface of the boat by examining the energy:

In reality, these two motions are completed at almost the same time, but by breaking them down into components, this mechanism can be approximated by the physics we have learned in this class.

Robert Spreeuw

Robert Spreeuw has been an associate professor of physics at the University of Amsterdam since 1996. He earned his PhD in physics at Leiden University in 1991, and he did postdoctoral research at NIST Gaithersburg and then at University of Konstanz. Professor Spreeuw has made significant contributions to the field of physics, as he has been published 125 times, and his research has been cited in thousands of other research papers.  Spreeuw was on the research team for a 1992 paper on donut-modes of laser beams, Orbital angular momentum of light and transformation of Laguerre Gaussian Laser modes, which was recently chosen as a “Classic Paper” by the Physical Review Journal. Their paper was given another honor when it was included in the journal’s 50^th Anniversary Milestone Collection, which selects papers that have made a significant contribution to the field of atomic, molecular and optical physics and quantum information. 

In a more recent paper, “Off-Axis Dipole Forces in Optical Tweezers by an Optical Analog of the Magnus Effect” published December 1^st, 2020, Spreeuw et al. showed that the Magnus effect, which causes spinning soccer or baseballs to curve, also applies to much smaller objects such as atoms or anything else that has a dipole moment. If the atom moves through a beam of light, then the light will exert a pressure on it, as air does for a soccer ball, resulting in a sideways force. One practical application of this discovery is that it allows physicists to be more precise when using optical tweezers which are used to move individual atoms because the optical tweezers experience the Magnus effect, and this knowledge can help them better predict how the atoms will behave. 

References 

 

https://www.miragenews.com/robert-spreeuw-s-donut-mode-paper-in-milestone-collection/

https://www.researchgate.net/profile/Robert_Spreeuw/2

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.233201

https://phys.org/news/2020-12-photonic-curveball-real-world-examples-soccer.html?deviceType=desktop

https://nl.linkedin.com/in/robert-spreeuw-b242197?trk=people-guest_people_search-card

Tree Branch Falling

  On Friday we had a snowstorm that resulted in about 4 inches of very wet heavy snowfall. At some point during the evening, we heard a crash that we first thought was just snow falling off the roof but when we looked out the window, we saw that a large tree branch had fallen- barely missing our car and lamp post in front of our home. So, I was curious about the force of the snow on the branch that made it fall and what would have happened if it had landed on the car instead of next to it. 

To get an idea of what forces were at play, I measured the tree branch, 5.6 m long and 18 cm diameter, and used those numbers plus some research into the density of a typical poplar tree, 385 kg/m³, to find the mass of the tree branch, (Volume x r density = mass) 73.11 kg.  Then I did some research on the density of the snowfall we received that night, 615 kg/m³, and used that to find the weight of the snow, (Volume x r density = mass), 20.99 kg. Next, I calculated the force of the tree branch without the snow, (Force =mass x gravity) 716.5 N, and then the additional force of the snow, 303.8 N. Next, I estimated how far the tree branch fell, about 24 ft or 7.3 m, and use that to find the velocity at which the tree branch fell, (v_f=v_o+at) 11.96 m/s, and use that calculation to find the kinetic energy, (KE=1/2 mv²) 7,446 J. Finally, I used the kinetic energy calculation and guessed how far windshield glass can bend, 0.01 m, and the pressure glass can withstand and found that if the back windshield had been hit, it most certainly would have broken as the tree would have hit it with 29.8 MPa and the glass can only withstand 6.89 MPa. Lucky for us, the tree landed on the lawn!

The physics behind Long Jumping and Hurdling In Track & Field

For nearly 7 years, Track and Field was part of my daily routine. While I mainly stuck to running, I was still given the opportunity to attempt other events such as pole vault. However, two of my favorite events to watch were always hurdles and long jump. Taking this course consequently piqued my interest in understanding the physics behind these events. 

In a hurdling event, many of the concepts we have learned can be applied. During this race, a person will run over a certain distance, jumping over hurdles in the process. Typically, this person’s body can be seen to be “tucked in” as they jump over the hurdles. This is a form most commonly used and seen. With beginners, it is a technique that is often taught very early on. In hurdling, it is most ideal to have a center of mass that is just above the hurdle so that the runner can reach the ground faster after clearing the obstacle. Therefore, the “tucked” position, which is better described as a lean, can be understood to help accomplish this. In addition, to be able to clear the jump, Newton’s second and third laws of motion must come into play. His second law, which states that the sum of the forces is equal to mass times acceleration (ΣF = ma), relates the mass of an object to the net force acting on said object. Taking this relationship into account, a person of a bigger mass must exert a greater force on the ground in order to effectively clear the hurdle. This also has to do with Newton’s third law, which simply states that for every action there is an equal and opposite reaction. Right before a jump, the forces acting on the runner in the Y-direction are that of gravity (FG) and the Normal force from the track (FN). To jump, the hurdler must exert a force on the track that will then equal a force exerted by the track on the runner. Conclusively, the more force exerted on the track by the runner, the easier it is for them to jump and clear the hurdle. Finally, one of the most obvious physics concepts observed during hurdling is that of projectile motion. On a day with minimal wind (and therefore air drag), the runner, while in the air during a jump, becomes influenced almost exclusively by the force of gravity. As a result, their horizontal velocity remains almost constant and their path taken is best described as a parabola. 

As expected, the same physics concepts are observed in a long-jumping event in which a person runs a given distance, gathering speed before jumping a seemingly parabolic path into a pit of sand. Other concepts, such as that of momentum which occurs right before the jump, can also be observed.

Sources: 

https://sites.google.com/site/thelongjumpproject/the-science-of-long-jumping

http://lsakelseyc1.weebly.com/newtons-law.html

Dr. Renzi and the Physics of a Single Cough

Dr. Emiliano Renzi from Loughborough University in the UK is a Senior Lecturer in Applied Mathematics who recently created a mathematical model that can analyze the motion of droplets resulting from sneezes and coughs. Dr. Renzi gained his Ph.D. in Environmental Engineering with Fluid Mechanics from the University of  Rome Tor Vergata in 2006. He then worked as an ENI-MITEI Energy Fellow at MIT for several years before working as a postdoctoral research fellow at the University College Dublin. At this university he eventually moved into the role of PI on an AXA Research Fellowship until 2015 when he took his role at Loughborough as a professor. 

His recent research- which he carried out in his bedroom do to the Covid-19 pandemic- is very applicable to recent recommendations regarding the spread of coronavirus, as he has taken to using his mathematical model to look at the distance that droplets from sneezes and coughs can travel with or without a mask. He determined that the trajectory of the droplets, the motion of which is initiated by a phenomenon known as buoyant vortex, is greatly affected by how people tilt their heads at the moment they project these droplets. This buoyant vortex is essentially the motion that occurs as a result of the hot and dense air that the droplets are combined with as they leave our mouths. He also found that larger droplets can travel horizontally over two meters and smaller droplets can be given some vertical velocity as a result of this vortex, contradicting previous studies which are informing social distancing regulations today. From these surprising results, Dr. Renzi is suggesting that people cough facing downwards in addition to using masks and maintaining adequate social distancing, as his model has shown the smallest displacement of droplets with these measures in place. 

https://phys.org/news/2020-12-mini-atomic-regularly-meters.html

https://www.lboro.ac.uk/departments/maths/staff/academic/emiliano-renzi/

The Physics of Moving a Car

 

Last night my sister packed up and tried to drive home, only to discover that she left a light on in her car, effectively killing the battery. One would expect the story to end here with an easy jumpstart and my sister on her way in under thirty minutes. However, there was one roadblock; the tree on my front lawn. My driveway is long and thin, slopes downhill, and consists of many loose stones. Because it is roughly the width of one car, one car cannot pass by another without going on the grass. My sister had conveniently parked in between two trees, making it impossible to pass her with my dad’s car in order to get their engines close enough to jumpstart her car. My dad decided that this left us with only one option: we must push the car up our driveway. 

Originally my brother and I had questioned this, wondering why we would not push the car further down the driveway. Surely the force of gravity would help us in pushing the car, effectively lessening the work we would have to do. This is because if we are pushing the car down the hill, the force of gravity in the x direction will be pointing in the same direction and will also contribute work in the same direction of our force. Pushing the car up the hill would be applying a force against both friction and the force of gravity, requiring more work (or a larger applied force) on our part to combat this and initiate movement. 

However, the important component we did not consider is that distance plays a role in the work done on a system. All other elements the same including friction, applied force, and force due to gravity, there will be some instance in which a larger distance required of the downhill push will make it less advantageous with a larger net work required. Because of the location of my house right after the trees, we would have had to push the car 20 meters into my backyard as opposed to 5 yards up my driveway.  

Setting net work equal to 0 J because this is what the work would be just before we push the car into motion, we can solve for the applied force necessary to move the car in each instance. Given that the downhill journey would require work for about 20 meters and the uphill journey would require work for about 5 meters, the downhill journey requires an applied force of 19000 N in comparison to the uphill applied force of about 3000 N. 

https://www.engineersedge.com/coeffients_of_friction.htm

https://hondanews.com/en-US/honda-automobiles/releases/release-3f07e0920c854addbd2284bad4720cee-2018-honda-fit-specifications-and-features

Nitroglycerin as a Heart Medication

 

    Nitroglycerin was discovered in 1847 by Ascanio Sobrero. Each molecule is composed of three nitrate groups bound to a chain of carbons, and the nitrate groups are powerful oxidizing agents that contribute to the compound's explosive properties. In 1864, Alfred Nobel discovered a process for making nitroglycerin more stable so that an explosion could be set off with a detonator. This creation was called dynamite. Despite its role as a deadly explosive, nitroglycerin also had important medical properties. Workers in dynamite factories noted that nitroglycerin eased chest pain. Scientists during the time were using amyl nitrite to dilate blood vessels and lower blood pressure, which increased the flow of oxygen and blood to the heart. By the 1880s, doctors realized that nitroglycerin was even more effective than amyl nitrite for treating chest pain. Scientists finally discovered in the 20th century the mechanism by which nitroglycerin relieves chest pain. The body converts nitroglycerin to nitric oxide which relaxes blood vessels and lowers blood pressure. We can examine how the velocity of blood changes as the diameter of blood vessels increases using the equation A1V1=A2V2. . When the diameter of the blood vessels increases, the area increases which increases the velocity. Bernoulli's equation shown below can be used to calculate the change in blood pressure.

Using the blood density and the two velocities of the blood from the previous equation, the change in blood pressure after blood vessel relaxation can be calculated to be a negative number, indicating that the blood pressure decreases. Nitroglycerin thus serves to relieve chest pain by relaxing blood vessels, which lowers blood pressure and increases oxygen and blood flow to the heart. Thus the heart does not have to work as hard to pump blood through the body. 

Sources

https://www.labroots.com/trending/videos/10322/nitroglycerin-a-life-saving-explosive

How can smaller animals brush off seemingly dangerous high velocity impacts?

 

Lately, our family welcomed a pair of kittens into our home. They've been a joyous bunch bouncing off of the walls playing until they're dead tired and curl on top of each other. When they play, they play hard, and often times when going full sprint for a toy they lose all sense of self-preservation and come crashing into the wall hard, or fall off of the table with a gleeful sense of abandon. Many times we audibly shudder, and my parents have wondered how they can shrug off such high-velocity impacts that if we were to experience would leave us bruised and in pain. Well, luckily this was something that physics could answer. The law of conservation of momentum states that the total momentum before a collision is equal to the total momentum after a collision. While this doesn't exactly translate into an inelastic collision with a wall, the principle holds true. Momentum can be broken down into mass x volume. If we were to impact a wall at a high speed, and a cat was to impact the same wall at the same speed, we would experience a greater momentum than the cat as our mass component of the momentum would be many magnitudes greater (a cat weighs generally around 9 pounds while the average American weighs generally around 160 pounds). As the collision with the wall greatly reduces our velocity we experience a change in momentum that's felt through the wall exerting momentum on us which usually results in a lot of pain. This change in momentum is so much less for a typical cat that they can just keep going whereas we would need a moment to recover.

Dr. Alison Saunders

Alison Saunders is an experimental physicist working at Lawrence Livermore National Laboratory. She graduated from Reed College with a Bachelor of Arts in physics, and went on to attain a Ph.D. in the subject from the University of California. Her research focuses on high power laser experiments measuring the conditions of dynamically compressed high energy density materials. This includes things such as radiation transport modeling, particle accelerator operations, and molecular dynamics modeling. One of her recent publications looks at how microjets are afster than speeding bullet which has implications in spacecraft shielding and planetary impacts. Another of her recent publications looks at ejecta interactions with regards to high power lasers rather than high explosive or gas gun sources. While these studies were a lot more complicated than the physics we were dealing with this semester I thought that the idea of particle accelerators and high impact collisions seemed really cool to study. 

Sources: 

https://aip.scitation.org/doi/10.1063/5.0028147

https://aip.scitation.org/doi/abs/10.1063/12.0000816

The Physics of Curly Hair

 A major problem in animation is accurately depicting the movement of curly hair. Seeing as only in recent times there has been a representation of diverse hair textures, animators and physicists are tasked with creating models that account for the mechanics of curly hair. From a physics standpoint, different degrees of curliness of a hair need to be described mathematically and how the properties of the curl change along the arc length of a hair.

Using lab experimentation, computer simulation, and theory, a team of researchers identified the main parameters for curly hair and simplified them into two dimensionless parameters for curvature (relating to the ratio of curvature and length) and weight (relating to the ratio of weight and stiffness). Given curvature, length, weight, and stiffness, their model will predict the shape of a hair, steel pipe, or Internet cable suspended under its own weight.

As a strand of hair curls up from the bottom, its 2-D hook grows larger until it reaches a point where it becomes unstable under its own weight and falls out of plane to become a 3-D helix. 

A curl can change phase — from 2-D to 3-D local helix to 3-D global helix, and back again — if its parameters change. Because a strand of hair is weighted from the bottom by gravity, the top of the strand has more weight under it than the tip, which has none. Thus, if the weight on a hair is too great for its innate curliness, the curl will fail and become either straight or helical, depending on the strand’s length and stiffness.