Lava Flow Physics

    Last weekend, I was able to travel to Syracuse with my Volcanology Class to conduct two experiments about lava flows using “man-made” lava. Lava is awesome, and is an excellent example of the relationship between chemical and physical qualities of materials and their physical behavior. 

    

    The velocity and style of a lava flow is primarily dictated by the lava’s viscosity, meaning resistance to flow. Viscosity is a function of multiple factors, specifically “the [lava] temperature T, the volume fraction of crystals [within the lava], and, to a lesser extent, the size and shape of the crystals” (Griffiths, 2000).  This is due to the nature of fluid flow, which is related to shear and strain. Shear stress is the force per unit area acting on a fluid, and strain rate is the rate of deformation experienced by a fluid when a load stress is applied (Harris, 2013). If the resistance to flow is high, more shear stress is required to achieve the same amount of change in strain rate than at low viscosity lavas (Harris, 2013). The relationship between stress and strain for lava (a Bingham fluid) is shown in the chart below (Harris, 2013).

    In our experiment, the beginning of the flow, when it was very hot, had a decreased viscosity and therefore a much higher velocity. As the lava flow traveled down the slope, its temperature cooled and it became more resistant to flow, eventually coming to a stop. 

    One goal of this experiment was to learn about lava tree formation. We didn’t quite succeed in creating lava trees (due to the scale of the experiment), but were able to make some interesting energy transfer observations. We set our lava to flow through two types of tree branches - a “wet” forest and a “dry” forest. We were curious to see if the hydration conditions of the wood had an effect on their ability to form lava trees. Something we didn’t even think about when designing the experiment was the effect the different trees may have on the flow itself. While watching the flow and when revisiting footage, we noticed that it seemed like the “wet” side of the flow took longer to catch fire than the “dry” side. Furthermore, the wet side had a decreased velocity compared to the dry side after exiting the “forest”. As a result, the wet side lava traveled less far than the dry lava. 

    This result can be explained by the conservation of energy. While fluid flow is more complex than linear kinematics, and this isn’t quite an inelastic or elastic collision, the law of conservation of energy can still be applied. When the lava passed through the wet forest, it required a greater amount of energy to ignite the trees than it did in the dry forest. So, more kinetic energy was lost and transformed to heat energy, and as a result the velocity decreased more. Then, kinematics can be used to explain resulting displacements. The lava with a greater initial velocity had a greater displacement before coming to rest, as explained by our kinematic equations (assuming they had equal accelerations). 

vf2 = vo2 + 2aΔx

0 = vo2 + 2aΔx

(-vo2) / 2a = Δx

Works Cited

Griffiths, R. W. (2000). The dynamics of lava flows. Annual review of fluid mechanics, 32(1), 477-518.

Harris, A. (2013). Lava flows. In S. Fagents, T. Gregg, & R. Lopes (Eds.), Modeling Volcanic Processes: The Physics and Mathematics of Volcanism (pp. 85-106). Cambridge: Cambridge University Press. doi:10.1017/CBO9781139021562.005

Physics of Diving

 

A Medical Application of Physics - Blood Pressure

I’m sure many of us in class are familiar with the inflatable cuff put around our bicep at the doctor's office that is used to measure blood pressure, also known as a sphygmomanometer. This device helps to distinguish between diastolic (low pressure) and systolic (high pressure) within a blood pulse, which make up the blood-pressure measurement in units of millimeters of mercury. However, this measurement can be confounded in certain situations and is often not taken frequently enough for individuals with certain conditions, even with all the smart technology many people wear on their wrists daily. In order to fill this blood-pressure data gap, Roozbeh Jafari, Deji Akinwande, and their colleagues have created a seemingly weightless and unobtrusive blood-pressure sensor that can be carried around everywhere. How did they do this you might ask? Well, they designed a temporary tattoo that is made of graphene and protected by an ultrathin polymer film shown in the image below. 

V = IR (Ohm’s Law) 

The 6 graphene electrodes, that stick to the skin through Van der Waals forces alone, are placed over the radial artery (and 6 on the ulnar artery) and measure the bioimpedance in the wrist which is converted blood pressure measurement through a machine learning algorithm, where bioimpedance is the resistance of tissue to an alternating electrical current. It takes the blood pressure of someone without even directly measuring pressure! Blood is rich in ions and serves as a great electrical conductor. As it pulses through a particular spot, the impedance drops which can be seen in the graph. The electrodes introduce a tiny current into the wrist and the induced potential measurement is proportional to the impedance. Additionally, the amount of time it takes for the pulse to propagate is correlated with the blood pressure of an individual (faster = higher BP), however, this isn’t so simple and involves a specifically curated algorithm. 

While we haven’t fully covered these topics in class, forces are definitely at play within this product, including the forces of the blood pushing against an artery or vein and the equal and opposite force suggested by Newton’s third law. This device takes into account many aspects of biophysics like biochemistry, fluid flow, pressure, and electrical currents, and I find this interconnectedness fascinating and pertinent to my personal study of physics.  

https://physicstoday.scitation.org/doi/10.1063/PT.3.5076

Why is it harder to walk up the hill to class?

 Why is it harder to walk up the hill to class?

Like the majority of the Colgate population, I find it harder to walk up the hill to get to class than to walk back down when going home. Walking up the hill to get to class when running late is not the most enjoyable part of my day, thus the process of leaving my dorm, walking up the never-ending series of stairs that exist on Colgate’s campus to get to my class all the way up the hill is therefore quite the feat.

But as a physics student, I wondered whether there was perhaps a mathematical and physics-related explanation for why the journey of walking up to class feels as if it is harder and longer than the walk back to my dorm.

As I live in 113 Broad Street, part of my walk to class includes walking up the hill. Assuming that my path is “ideal” and represents a straight walk up a slope, an analysis of the forces on me can be done.

When I am walking up the hill, there are two forces acting on me - the force of gravity and the force of friction. Assuming that I realize I am desperately late for class, I gradually increase the pace at which I am walking, thus my acceleration is greater than zero. Thus, as I exert acceleration  in the +x direction, both gravity and friction exert force in the -x direction, resulting in an overall decrease of acceleration than my own acceleration.

When I am walking down the hill, there are still two forces acting on me - the force of gravity and the force of friction. Assuming I am excited to race back to my room, I gradually accelerate the pace of my walk. This time, as I am walking in the -x direction, gravity is acting upon me in the -x direction as well (while friction acts in the +x direction). Thus, the magnitude of my overall acceleration is increased when walking down the hill, as I no longer have two forces acting in the opposite direction of my velocity (and acceleration), and instead only have one. 

Thus, the reason why it seems like a more difficult journey to walk up the hill to get to class is because there are forces acting in the opposite direction than the direction I am moving in, thus slowing me down and requiring a longer walking time!

Professor Ariel Schwartzman

 

Dr. Ariel Schwartzman is a professor of particle physics and astrophysics at the SLAC National Accelerator laboratory at Stanford University. Professor Schwartzman earned his Ph.D. in Experimental Particle Physics from the University of Buenos Aires. He then worked as a R. H. Dicke Fellow at Princeton University and a Panofsky Fellow at Stanford University before achieving the title of full professor at the SLAC National Accelerator laboratory in April of 2022. The Schwartzman lab encompasses undergraduates, graduate students, and postdoctoral fellows who collaboratively work to develop new detectors, machine learning programs, and statistical analysis methods. The lab is engaged in two large-scale collaborative research projects. The first is the ATLAS Experiment at CERN, where the Schwartzman lab develops machine learning algorithms to investigate pattern recognition and ultrafast-timing detectors. His lab also participates in the MAGIS-100 Experiment at Fermilab. This experiment aims to use the most advanced atom interferometer, a device using two light beams to make precise measurements, to search for a particular kind of dark matter called ultralight wave dark matter. The MAGIS-100 Experiment also seeks to advance the study of quantum mechanics by increasing the precision of measurement and improving particle collision technology. In particular, the Schwartzman lab is developing a 3D imaging system for this experiment focused on integrating atomic control and calibration technology. 

Professor Schwartzman’s most recent work was published in the Journal of Instrumentation, titled “Novel light field imaging device with enhanced light collection for cold atom clouds.” Schwartzman and his colleagues at Stanford University constructed a precisely arranged dome of mirrors to optimize ultra-low light photography at the atomic level. Using strontium atoms, the researchers sought to improve the clarity of atomic cloud imaging by first shining a laser on the atoms, which is a standard technique. However, an intensity too high will prohibit viewing the clouds in detail whereas too little light will not generate a clear image at all. The researchers cleverly realized that carefully arranging mirrors to reflect light that had already traveled through the cloud back into the lens would enhance the detail and simultaneously provide additional image angles of the atom. Members of the Schwartzman lab seek to create a smaller version of this mirror imaging system to develop a technique to generate precise 3D images of atomic clouds. 

https://www.sciencedaily.com/releases/2022/08/220819142947.htm

https://iopscience.iop.org/article/10.1088/1748-0221/17/08/P08021

https://sites.google.com/stanford.edu/schwartzman-lab/home?authuser=0

https://atlas.cern/about

https://magis.fnal.gov/

https://www.linkedin.com/in/ariel-schwartzman-0544b72/

Understanding and Improving Kick Drum Technique

For over eight years, my brother and I have enjoyed playing and writing music together. As I strum chords and pick an array of notes on the fretboard of my guitar, my brother is working tirelessly behind the drum set. As he is a true hard rock/metal drummer, it always amazed me how quickly he could play the kick drum with his feet. 

Not only do drummers like my brother have to keep a fast tempo throughout the song, but they have to play complicated rhythms with their feet using a double kick drum pedal (shown below). Each hit of the kick drum should strike the drum with a significant and similar impact compared to other hits; playing the kick drum too quietly loses its punchy sound, and this is particularly noticeable while playing quickly as softer hits become difficult to distinguish. 

(Image of a double kick drum pedal)

The force exerted on the kick pedal by the drummer should ideally be the same between hits. As the beater (the circular piece that makes contact with the drum) strikes the kick drum, it exerts a force on the head of the kick drum. By Newton’s third law, the drum head exerts an equal and opposite force on the beater. The equation for force is shown below: 

F = ma

Here I ignore the force of friction and assume that all kinetic energy is transferred from the pedal into the beater that strikes the kick drum (therefore treated as the same direction of motion). The mass of the drummer’s foot and leg also remain the same. Therefore, in order to hit the drum with the same force, the acceleration of the beater, and therefore the acceleration of the drummer’s foot and leg, must be the same between hits. To calculate the work done on the kick drum by the beater, the equation for work can be used as illustrated below: 

W = F||d

Because the displacement of the beater remains constant, the force exerted by the beater is directly proportional to the work done on the drum head. The net work is equal to the change in kinetic energy as shown below:

Wnet = delta KE = 1/2m(vf^2-vo^2)

Similarly, in order to do the same amount of work on the kick drum, the final velocity of the beater must be the same given that the initial velocity is always zero (resting position of the beater). 

To connect these ideas together and translate them into a practical application, we need to investigate the nature of acceleration, which is shown below:

a = delta v/delta t  

As already established, in order to exert the same force and do the same work on the kick drum to maintain a pleasant and punchy sound, the acceleration and change in velocity must be equivalent between hits. Therefore, the drummer must extend their legs in the same time interval to maintain a steady acceleration with the same change in velocity. This becomes particularly challenging while playing quickly. If the drummer's legs extend more slowly, the acceleration will decrease and less force will be exerted on the kick drum, making a quieter sound. This decrease in force translates to less work done on the drum head, also corresponding to a slower final velocity of the drum beater. Consequently, as more experienced drummers practice and improve their kick drum technique, they are able to increase the rate at which they can return their foot and leg to rest position after striking the kick drum. This permits drummers to strike the kick pedal with a near-maximal force for each hit in rapid succession. Using this information, if drummers notice that their kick drum playing sounds inconsistent, their legs are not accelerating at the same rate between hits. They should work to strengthen their muscles to increase the acceleration of the pedal and kick beater while improving the time they can return their legs to rest position, allowing them to exert a similar force shortly after striking the kick drum.

Physics in DNA Mechanisms

How Physics Plays a Role in Genetic Mechanisms

The Use of Spider Silk to Support ICF Targets: Research by Mark Bonino

 When looking for someone doing physics research that I find interesting, I didn’t have to search very far! My father, Mark Bonino, is the target production manager, and is in charge of a group of assembly technicians who build 2600 targets each year at the University of Rochester Laboratory for Laser Energetics. Besides that, he does metrology and characterization using SEM, AFM and optical microscopy. He received a Bachelor of Science degree in Physics from St. John Fisher College in 1994, began working full time at the University of Rochester Laboratory for Laser Energetics in 1995, and completed his part time graduate studies in Materials Science in 2003. 

 

In general, Laser Lab employees support experiments in nuclear fusion (using the OMEGA Laser system – a system as big as a football field!) in order to find alternative energy sources. As interesting as this whole process is, I wanted to instead highlight a specific part of it using the research Mark did as he was working towards his Master’s degree - it more closely relates to what we have been talking about in class!

 

Mark focused his research on the implementation of spider silk to support direct-drive inertial confinement fusion (ICF) targets used in the OMEGA laser system, specifically because of the silk’s physical properties like stiffness, elasticity, tensile strength, and energy to break. The elastic properties of the silk are helpful when it comes to this application, because the capsule needs to remain stationary while at cryogenic temperatures before it is shot.

 

Looking specifically at the strength of the silk, tensile tests were done where samples were placed between two grips and pulled by a crosshead. This is where our class work relates, as Hooke’s law directly relates to this test (F_s = -kx)! The modulus of elasticity is analogous to the spring constant (k), F is the force applied, and x is the displacement. As we have learned, there is a linear relationship between the applied force and displacement, but Hooke’s law only works for small deformations. Large deformations leads to a non-linear relationship, and the law no longer applies. The point where the slope changes from linearity is called the yield point. It is here that the material is being strained beyond its elastic region, and any deformation after this point will not allow the sample to return to its original length. From the tensile test, three regions were identified: (1) the elastic region, (2) the inelastic region, and (3) the region after maximum loading. In the elastic region, the data follows a linear curve defined by Hooke's law.  

 

It’s so interesting to understand a part of the research that I have heard about for years on end, and exciting to see some of the concepts we have learned about in our class being applied to upper-level research in the field of Physics!

 

If anyone is interested in learning more about this materials science research, Mark’s thesis is linked below.

 

https://www.lle.rochester.edu/media/publications/documents/theses/Bonino.pdf

Apple Picking

This weekend I went to an apple orchard. Last year, I got to pick off the apples directly from the tree but this year they were all on the ground. 

I began to think of this situation in terms of forces, and how the tension force holding up the apple may decrease as it gets colder or with time (a lot of biological assumptions are being made). Assuming the apple is 0.15kg, what is the tension force at which the apple will fall?

Forces	x	y
FT	-	FT
FG	-	-mg
Total	-	may

may=(0.15kg)(0m/s2)=0N

0N=FT-mg

FT=mg=1.5N

Once the tension force is less than the force of gravity, the apple will fall from the tree. 

Though in reality, there are additional forces acting on the apple. In this next scenario, I will consider wind (6.5 N) and an angled tension force (30o). What is the tension force at which the apple will fall? (If the wind accelerates the apple by 0.5 m/s).

Forces	x	y
FT	-FTsin(30o)	FTcos(30o)
FG	-	-mg
FW	FW	-
Total	max	may

FW-FTsin(30o)=max

6.5N-FT(0.5)=(0.15kg)(0.5m/s)

FT=12.9 N

The tension force of the apple is much greater with an angled tension and the force of wind. This conceptually makes sense because the force of tension is working against the additional force of wind. For the apple to fall, Fw > FTsin(30o), and/or FG > FTcos(30o).

NASA Smashes Into An Asteroid

    Hi everyone! Last week, NASA launched a new planetary defense tactic: asteroid smashing. NASA deployed a Double Asteroid Redirection Test (DART) to hit an asteroid to test its ability to protect Earth from extraterrestrial threats. Although this sounds like the premise of a sci-fi movie, it really is real life. And the superheroes who defended Earth on this mission are none other than Johns Hopkins physicists! 

Credits: NASA/Johns Hopkins APL

    Two asteroids about 7,000,000 miles from Earth (over 112 million kilometers!) were the targets in this situation in order for NASA to see if they could successfully detect and destroy any potential threats by using the DART. They completed this mission by using the physics we have seen in Physics 111! 

    NASA guided the 570-kilogram box-shaped spacecraft into space, but things got intense through the final 90, 000 kilometers of space when the DART came into the orbit of the bigger asteroid, Dimorphos. The DART's velocity increased until 6268 m/s when it crashed into the asteroid and slightly slowed the asteroid’s orbital speed. Smashing an asteroid was as easy as solving a high speed projectile motion problem! 

https://www.nytimes.com/2022/09/26/science/dart-nasa-asteroid-dimorphos-contact.html?smid=url-share

How Water Effects Friction When Walking Downhill by Ethan Riggs

The past few days here on Colgate's campus have been very dreary and full of rain. Since I and many others live down the hill we have to deal with the slippery slope that comes about due to the rain. On one of these fateful thunderous nights, the rain was coming down particularly hard as I approached the hill leading past the library to Willow Path. As I walked down the hill I could feel just how slippery the asphalt was when water was on it. I remember testing it out by swinging my leg and having it slide right across the ground with little resistance.

What is happening here? It seems that when it rains the water makes the asphalt more slippery because of a lower friction force between my shoe and the ground. If we think back to the equation Ffr = 𝜇k FN we notice that the coefficient of kinetic friction is directly related to the force of friction. We learned in class that the coefficient of friction is a number that is specific to the two materials in contact. When comparing the force of friction between my shoe and the asphalt it can be concluded that Ffr is greater when there is no rain and lower when there is rain. Since the normal friction does not change, we can then make the assumption that when rain is present on the asphalt the force of friction between my shoe and the asphalt is lower than without the rain. This supports what we talked about in class about the coefficient of friction being specific to the two materials interacting and can change when one of the surfaces is altered.

I have had fun thinking about how physics affects my daily life and will continue to see the world differently while also being safe when walking down the many campus hills.