# Physics End of the Semester

• Updated July 18, 2021
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Now that we are at the end of the semester, I have to say that I enjoyed this physics class a lot more than my previous one taken in high school. That being said physics is not my favorite subject but I realized it has to do with everything present in our lives and that I should probably pay attention in this class. Even though I disliked the tests and struggled with some of the material learned in this class, I can say that I slightly like physics if it doesn’t deal with driving off multiple cliffs and then landing in the ocean.

## Definitions

### Force

A force is defined as a push or pull on an object by either contact or a field force that causes a change in motion. Force is a vector, represented by Newtons, N, and can be found multiplying mass times acceleration. The acceleration is directly proportional to its applied force with mass and acceleration being inversely proportional.

### Momentum

Momentum is dependent upon mass and velocity and can be found using the equation: p=mv. Momentum has the SI units of (kg x m/s) and refers to the movement of an object mass. The change in momentum of an object uses force and refers to Newton’s first law ‘an object in motion stays in motion, an object at rest stays at rest unless acted upon by an external force’. Momentum also equals impulse.

### Torque

Torque is something I have trouble understanding but I define it as the force that causes angular acceleration and can be found by using Torque= rF, where r is vector length and F is force acting to move the object.

### Inertia

Inertia is the resistance to the change of motion. Inertia deals with Newton’s Laws of Motion that is defined as ‘an object in motion stays in motion, an object at rest stays at rest unless acted upon by an external force’. An object with greater mass has more inertia as it takes more force to move the object using the equation: Force= mass x acceleration.

I was early and present for every physics lecture which gave me extra preparation before class if we had a test or a quiz. I also did the practice problems given and read over my notes after lectures to see if I understood the material and if not I looked in the book for more help or found online videos. The times I would be confused during lectures was when I would leave to the bathroom and come back to extra equations, which in return I took to Blackboard to read the lecture notes you posted. I did not go to tutoring for this class but I feel like it would have been to good benefit if I did.

Ultrasonic waves produce small images using its high frequency, greater than 20 kilahertz, and short wavelengths by the reflection of two materials of different densities and absorption of the waves. Ultrasounds use transducers to send sound waves into the patients body, with the waves (or echoes) bouncing off different tissues in the body and returning to the transducer to be processed into a black/white ultrasound image of the internal organs. The mechanical waves that propagate through the tissue generate the sound waves that are transmitted and received by the transducer.

The mechanical waves are produced using the piezoelectric effect that uses electrical contact to opposite faces of a crystal, causing the crystal to vibrate and emit a sound wave; this effect of the crystal is reversible to generate and receive ultrasonic waves. The accurate transducer must be selected to have adequate frequency and better resolution with deep structures using low frequencies and more penetration for deeper structures and higher frequencies for better resolution of shallow structures. Shallow structures reflect first and will be displayed at the top of an image while echos from deeper structures take longer to return and displayed at the bottom of an image.

To compensate for deeper structures, an increase in time gain compensation must happen to product images in real time and brightens the visibility of the structure. Gel is used as a coupling agent or a medium so that the sound can travel through the body. The gel is the contact between the body and the transducer, where the tight bond traps air between the two to reflect and transmit sound waves to the tissue that needs to be imaged. The percent of sound wave intensity reflected can be calculated using the formula: PR=((pipt)/(pi+pt))2×100; with pi the materials density and pt the material it strikes density.

1. Ultrasound waves are used to measure reflectivity and absorption of tissues to produce sound waves and a small image.
2. Ultrasound waves have short longitudinal wavelengths and high frequencies that are greater than 20 kilahertz. A longitudinal wave is when the particals move in the same direction as the wave.
3. An image is produced when a transducer probe, containing piezoelectric crystals, has a voltage/current applied to it which causes the element to expand and contract creating a pressure wave to propagate through tissue in the body. The echos reflected from the tissue returns causing the crystals to vibrate, and return to the transducer elements to be converted to an image. This method of transforming electrical energy into mechanical energy is the piezoelectric effect.
4. The pulse-echo method (Beta Mode) produces pulses of the ultrasound waves and are used to produce an image.
5. Shallow structures reflect first and displayed at the top of an image while echos from deeper structures take longer to return and are displayed at the bottom of an image. This process is done rapidly enough and displays moving images in real time.

When I first learned of there being a presentation instead of a final, I was happy because there was no test but then I realized I would have to speak in front of the class. This made me nervous because I would have to present for 10 minutes in front of mostly complete strangers at that time. Another inhibition I came across in the beginning and currently was that if someone asked me a question or to explain something my mind would go blank and not know how to answer it and explain it to the best of their knowledge. The other inhibition I thought I was going to face in while working on this presentation was the motivation to not work on it when I had finals to study for instead.

Throughout the semester, our class became closer where we got over the awkward stages and began communicating more to each other. The increase in communication with everyone has made me feel more comfortable and confident enough to be able to speak in front of everyone. My inhibition with being confronted with questions, I have asked my roommate to ask me some but I know her personally so I will have to see how I do when I present next Wednesday. My lack of motivation in the beginning with the presentation was just pure laziness until I realized that this is a good portion of my grade and could influence my grade up by a letter grade if I do well on it.

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