Physics Class Review

Physics is the study of the relationship between energy and matter. It's basically a study on why everything in the world acts the way it does. Through physics, you learn all about how light works, why objects move/rest the way they do, and so much more.
I thought this class was super fun! I was dreading the six hour classes that we had,  and I was terrified of the idea of having to spend six weeks with a boring teacher. While the classes were a bit unbearable at times, Mr. Blake definitely made class more interesting, with his joking around while still managing to get the points across. We always had interesting lab demos, which provided a hands-on learning process as well as much appreciated breaks from sitting still for so long. Everyone in the class seemed to get along well, and because of that, the class atmosphere was always laid back and comfortable.

We learned so much in this class! I'm not very confident that I'll remember everything we learned in a few months from now, but we covered so much in the past six weeks.  
Unit 1 was all about introducing ourselves to physics. We didn't really learn anything actually physics related, but we did learn a bunch of stuff anyway. We learned about the different graph shapes and the relationships the x and y axes had with each other, as well as the difference between accuracy and precision. Accuracy is based on how close you are to a certain value, while precision is based on the consistency you have of hitting the same value.  Besides that, we reviewed scientific notation and how to do conversions.  
Unit 2 is where we actually began learning actual physics concepts, and this unit was all about kinematics, or the study of motion. We learned how to make motion maps, and the differences between scalar and vector quantities. Scalar quantities, are measurements that have magnitude (muchness), while vector quantities have both magnitude and direction. We also learned a lot of vocabulary words and their definitions, such as position, distance, displacement, velocity, speed, and acceleration. We also began using graphs more, learning how to draw position vs. time graphs, and velocity vs. time graphs, as well as the three graphing rules: 1) the slope of a position vs. time graph is velocity, 2) the slope of a velocity vs. time graph is acceleration, and 3) the area under the "curve" of a velocity vs. time graph is the distance traveled.
Unit 3 focused on acceleration. We learned how to draw acceleration vs. time graphs, just by looking at a velocity vs. time graph. We also learned the three equations that became very useful for not only this unit, but many after. They were d=1/2at^2+Vot (d,a,t), V=Vo+at (v,a,t), and V^2=Vo^2+2ad (v,a,d). With these equations, we learned how to solve word problems, and the process on how to solve word problems effectively.
Unit 4 was all about projectiles, which was confusing, since we started having to pay attention to two different axes that were independent of each other. Because the axes were independent of each other, we had to use multiple equations for the problems, which sometimes became confusing, but was manageable after a while.
Unit 5 was about forces in equilibrium, which involved vectors and using trigonometry. We had to draw many diagrams of vectors in this lesson, and learned a method for finding whatever it was we were looking for, by using Mr. Blake's patented bureku technique, which involved breaking up the diagonals of vectors. We also learned about force, which is a push or a pull and is a vector quantity. We learned Newton's three laws of physics, as well as how to draw free body diagrams, which provided us with a better understanding of the problems we were doing.
Unit 6 was kind of the same thing as unit 5, since it was pretty much entirely based on Newton's second law of physics, which stated that acceleration was equal to the net force of an object divided by its mass (a = fnet ÷ mass). We learned about pulleys, which change the direction of force, and drew a lot of free body diagrams in this unit as well, which was helpful.
Unit 7 focused on momentum and collisions. We learned that momentum was mass times velocity (p = mv), as well as the law of conservation of momentum, which, as the title hints at, stated that momentum, in a close system, is always conserved. We also learned what impulses are (changes in momentum), how to find them (impulse = force x change in time), as well as a new graphing rule, which was that under the curve of a force vs. time graph, the area is equal to impulse.
Unit 8 was all about energy and work. We learned the Law of Conservation of energy, which states that energy cannot be created or destroyed, it only changes form. We also learned about the different types of energy: there is kinetic, which is the energy of motion, potential (gravitational) energy, and spring potential energy. We also learned about work, which is the change in energy, and Hooke's law, which helps you find the force of a spring.
Unit 9 was based on waves and sound, which was both confusing and interesting. We learned about vibrations, which are wiggles in time, waves, which are made up of vibrations in space, and media, which is the stuff that carries the waves. We also learned about different parts of waves, like the wavelengths, amplitudes, periods (amount of time it takes for one complete cycle to occur), crests, troughs, nodes, and anti-nodes.

Unit 10 was one of the hardest units, and it was all about light behavior. We learned about what light was, the speed of light (3x10^8 m/s), and what a light year was. We also learned the differences between opaque and transparent, as well as what the electromagnetic spectrum was. We learned about different types of reflections, such as specular reflections and diffuse reflections. Besides that, we learned about white light, which is light that carries all the frequencies of ROYGBIV, and what the color wheel of light was. Not only that, but we learned about why the ocean and sky are blue, and how rainbows are made. The Law of Reflection was also a big topic, as well as what refraction is and how to find the angles of incidence, angles of refraction, and what the index of refraction was. Lastly, we learned about parallel rays and focal rays, and how to find the image of an object in a reflection.

I think what I liked the most about this class (I talked about this earlier), was the overall atmosphere of the class. Despite the grueling hours everyone spent in class, we all seemed to have fun in class. The labs were fun and entertaining, and Mr. Blake always had an energetic personality, and his energy was infectious. I think the only thing about the class that I would improve, is by giving us maybe a few more breaks in class, since two breaks isn't enough. Either that, or take 10 second breaks to just stretch and jump around a bit. Other than that, I had a really fun time in class this summer, and I would actually be willing to take a class like this again... I also had really awesome table partners, so they just made this class even more fun.

Physics Unit 10 (Part 3)

Today we learned more about refraction, which was incredibly confusing, in my opinion. Refraction is the changing of wave speeds due to changes in wave media, and is dependent on how optically dense the medium is. The main thing we focused on was Snell's Law, which stated that the index of refraction of a ray of light before it changes media, multiplied by the sine of said light's angle of incidence would be equal to the index of refraction of the light when it changes media, multiplied by its angle of reflection (did that even make sense?). The equation for Snell's Law is n1sinθ1 = n2sinθ2 (θ = theta). In order to find the index of refraction, you divide the speed of light by the speed of light in the medium ( n = c÷v). Also, if you have the index of refraction of a medium, you could use the equation to find the speed of light in the medium (v = c÷n). For example, you were trying to find the speed of light in glass, you would take the speed of light and divide it by glass' index of refraction, which is 1.5. So you would do 3 x 10^8 ÷ 1.5, to get 2 x 10^8 m/s. We also learned about critical angles, and how to find them with this equation: sinθc = n2 ÷ n1. With your knowledge of what the critical angle is, you can find what the total internal reflection is, which is when the light's reflecting inside the medium.

When the ray of light changes from a fast medium to a slow medium, the light will bend towards the normal (perpendicular to the surface). However, when the ray of light moves from a slow medium to a fast medium, the light will bend away from the normal.

We also learned the differences between diverging lenses and converging lenses. A diverging lens is when multiple lights are being shined into a lens, and they are all refracted away from each other. A converging lens is the opposite, and when multiple lights are shined into them, the rays of light refract and converge at a focal point. Lastly, we learned about two types of rays. The first ray is a parallel ray, which is from the object being parallel to the optic axis through the focal point on the other side. A focal ray, is from the object through the focal point on the object's side through the lens, then parallel. 

Physics Unit 10 (Part 2)

 We learned a lot in class today, which, in all honesty, was pretty painful. We learned a lot more about lights and reflection, which was both interesting and incredibly confusing, so please bear with me as I attempt to explain everything.

 First of all, there's this type of light called white light. White light has all frequencies of ROYGBIV, which means that it has the frequencies of all the colors of the rainbow. When an object is a certain color, that means that the object is reflecting the color that you are seeing, while absorbing all the others. Also, black absorbs all the colors while white reflects them, so if you are ever planning on walking around in a desert, make sure you're wearing a white shirt when you do so. Wearing a white shirt will keep you a lot cooler than if you were wearing a black shirt. Now that you (hopefully) understand white light, let's move on to colored lights (because I am unbiased like that). So, in the pictures on the left, you can see my teacher, Mr. Blake, standing in red light and green light, and even though it might be hard for you to determine, he's wearing a red shirt. So, since his shirt is red, you know that it is absorbing all other colors except for red, which is being reflected. When he's standing in the red light, his shirt is going to look red, because it is still reflecting red back. However, when he is standing in the green light, his shirt will look black. The reason his shirt looks black, is because there is no red light for it to reflect at all, which causes it to look black instead.

The picture on the left is of the Color Wheel of Light, which has the primary colors, also known as the main colors of light. It also shows what color two lights make when they are shining into each other, as well as the complimentary colors, which are colors on the opposite sides of the wheel that, when added together, make the color white. Unfortunately, you can't think of the color wheel of light as anything other than related to light. I know that it's confusing, and you want to think of it with the same concept you would paint, but when you mix the colors together, they make white, not brown.



 This next picture, show my Mr. Blake's three shadows, which are the results of shining three different lights at him, a red light, a green light, and a blue light. As you hopefully noticed, those are the primary colors that I listed above. The order of the lights from left to right were green, blue, and red. You can tell, because the shadow on the left is cyan, which means that it had the lights green and blue on it, while Mr. Blake blocked the red light. The middle light is yellow, which means that green and red were shining together to create that color while Mr. Blake blocked the blue from interfering. Lastly, there is magenta, which is made up of red and blue, with Mr. Blake blocking the green light. You can also see that the sort of square around the shadows is white-ish, which is a result of the three primary colors mixing together.



A common misconception people have is why the sky and ocean are blue. Most people think that they're blue because they are reflecting each other, but that is actually wrong. The sky is blue (actually more of a violet color, but we can't really see that), because blue wavelengths are scattering in the atmosphere due to nitrogen. The ocean is blue because the water absorbs the ROY in ROYGBIV, leaving the green, blue, indigo, and violet to be reflected. Also, a really cool fact that Mr. Blake told us today had to do with why fish are red, since you'd imagine they would want to be darker and not draw attention to themselves. In actuality, because the red, orange, and yellow frequencies are being absorbed in the water, there is no red light to reflect off of the fish. This means that the fish appears to be black in the water, and keeps it safe (isn't that awesome?!).

 We learned one of the Laws of Reflection, which stated that an angle of incidence equals the angle of reflection (works for all mirrors). Also, all angles are relative to the normal, which is perpendicular to the surface. This means, that when you shine a light at a mirror and you imagine a perpendicular line coming up from where it hits the mirror, the angle the light is reflecting at will be the same as the angle of the original light... if that made any sense at all. If you look at the picture to the left, you can see Mr. Blake shining a laser at a mirror. The light that is coming out of the laser is the light with the angle of incidence. The point where you can see that the laser hit the mirror is where the normal would be. You can see where the light reflects off the mirror, which is the angle of reflection. Relative to the normal, both angles will be equal.

Lastly, we learned that while you can't see light normally, when it is foggy, you can. This is (I believe) because of the light reflecting off the little droplets, which then go into your eyes, allowing you to see them (doesn't the picture on the left look amazing, they're kinda like extremely long, narrow lightsabers!!).

So, if you can only take one lesson out of this whole blogpost, let it be this: next time your car breaks down in the middle of an incredibly foggy forest at night, instead of heading into the woods to inevitably find the creepy cabin and get yourself killed, pull out your laser and have a lightsaber battle with your friends until morning (or the fog goes away, whichever happens first).

Physics Unit 10

The picture above, in case you didn't know, is a picture of the sun. Now I know everyone who is reading this is asking themselves "why is there a picture of the sun?", and I, being the incredibly generous person that I am, will tell you. In this unit, we are learning all about light behavior (woohoo, light behavior!!). In class, we pretty much spent the whole time learning a lot of vocabulary, as well as all about the electromagnetic spectrum.

First of all, light is a transverse, electromagnetic wave, and doesn't need a medium. This makes sense, since light travels through space. The speed of light, when written as a variable is a lowercase c, and is 3 x 10^8 m/s. In other words, the speed of light is 300,000,000 m/s. A light year, on the other hand, is the distance light travels in one earth year. An interesting fact to think about, is that the only reason you can see anything, is because light is reflecting off the objects and going to your eyes. If the light didn't reach your eyes, you wouldn't be able to see anything.

Two important terms that we learned today are opaque and transparent. When something is opaque, that means that the object is impenetrable by light. Transparent, is the exact opposite of opaque, which means that it is penetrable by light and other electromagnetic waves. An example of the two terms is saying that glass is transparent to visible light, but your eyelids are opaque. In other words, light can go through glass, but can't go through your eyelids (thank goodness for eyelids!). 

Lastly, we learned about the electromagnetic spectrum, which is the range of different wavelengths based on types of known waves. The electromagnetic spectrum is based on ROYGBIV, with red as low energy, and violet as high energy. Frequencies, wavelengths, and energies govern the different wave properties. While I'm not going to go into detail of the amount of hertz each category has, I am going to list them in order from highest to lowest energy rays instead. First, with the highest energy rays are gamma rays, which are responsible for nuclear reactions and cosmic rays, not to mention The Hulk. After gamma rays, there are x-rays, which are high energy waves that can cause mutations in cells, skin burns, and cancer. X-rays are opaque to bones and transparent to skin and muscle, which is why we used to use them whenever we had to see if we had broken bones. After that, there are ultraviolet (UV) radiation, which is beyond the visible region of the spectrum. After UV radiation, there is the visible spectrum, which has frequencies that are visible to humans. This is a very small portion of the spectrum, however, and it makes me wonder about all the things that we aren't seeing (oooh, spooky, right? Nah, not so much, actually...). After that, there is infrared, which is in the region with frequencies just below the red. Infrared gives off heat energy and radiation, and its frequencies are most absorbed by water. After infrared, there is the energy that comes from microwaves. Microwaves have the same energy is used in speed guns, and wireless transmitters. Lastly, but definitely not least, we have the waves that come from radios and televisions, which give off the least amount of energy rays out of everything else. 

I thought I'd put another picture, because who doesn't like pictures of sunsets?

Physics Unit 9 (Part 2)

We learned more about waves and sound in class on Friday. The picture above is an illustration of the range of human hearing (please excuse my bad drawing). As you can see in the picture, humans can hear sonic frequencies, which are between 20 Hz and 20,000 Hz. Animals such as whales and fish can hear infrasonic frequencies, which are from 20 Hz and down. On the other hand, elephants, bats, and dogs are a few animals that can hear ultrasonic frequencies of 20,000 Hz and more. (all of my information about animals came from the internet...)

Through a lab that involved tuning forks (I keep calling them pitch forks in my head, it's a problem), a graduated cylinder almost completely filled with water, and a tube of some sort. The purpose of the lab was to learn how to find the speeds of waves. First, we would hit the tuning fork on something harder so it would vibrate and create a pitch due to its natural frequency. Once the tuning fork is creating a sound, we would put it over the tube, which was submerged in the water, and then lift it slowly until the sound of the tuning fork was made by the rest of the graduated cylinder. When that happened, we were able to find the wavelengths of the tuning fork was making, by measuring the length of the tube from where it came out of the water to the bottom of the tuning fork, then multiplying that by four. Once we found the wavelengths, we were able to find the wave speed by multiplying the wavelengths by the frequencies of the tuning forks.

In class we also learned more vocab words, such as:
Refraction = the bending of waves due to changes in the medium
Reflection = the bouncing of waves
Dispersion = the spreading out of waves
Standing waves = waves that look like they're not moving
Natural frequency = the frequency of an object wants to vibrate at after an external disturbance
Resonance = the increase in amplitude of a system exposed to a force at an object's natural frequency
Sound = a vibration that causes a longitudinal wave
Pitch = the frequency of sound
Speed of sound in air = 331 + .6(Tc)

• 331 = the speed of sound in dry air at 0°C
• Tc = temperature in celcius    

Physics Unit 9

We started Unit 9 today, which was both interesting and incredibly painful. This unit is focused on waves and sound, although we haven't really covered much of sound yet. We pretty much spent the whole day learning about waves, how to graph them, the different parts of them, and so on.

The picture on the left is a wave. A wave is a vibration in space, and a vibration, is pretty much a wiggle in time that moves back and forth between points. Anyway, there are many different parts of a wave. There is a thing called a loop, which is pretty much the curve of the wave. In this picture, there are three loops. There is also the crest, which, as shown in the picture, is the top part of the loop, while a trough is the bottom part. Both the crest and the trough are antinodes, which are the parts of the wave that move. A node, on the other hand, is the part of a wave that doesn't move, which is located in between the loops of a wave. Next, there is the amplitude. An amplitude is the distance between a crest and the equilibrium point of the wave, or the trough and the equilibrium point. Lastly, there is a thing called a wavelength. A wavelength, is measured from two identical portions of the wave. As you can see in the picture, the wavelength starts at an equilibrium point and ends at the next equilibrium point where the wave is travelling in the same direction, in this case, down. An easier way to find the number of wavelengths a wave has, is to count the number of loops the wave has, and divide it by two. In this case, there are three loops, so there are only one and a half wavelengths.

Here is some more important vocab we learned:
Medium = the thing that carries the wave
Period = the amount of time it takes for one complete cycle to occur
Frequency = ƒ = how many cycles pass in a second. Unit = Hertz (Hz) = 1 cycle ÷ second
Transverse waves = when the wave energy moves perpendicular to the wave velocity
Longitudinal waves = waves in which the energy moves parallel to the wave velocity
Principal of Superposition = says multiple waves can exist in the same space
Constructive Interference = if waves collide with each other and are both positive or both negative, they will create a loop twice as large as their original size. However, if a positive and a negative wave collide, their opposite forces will cause a flat wave.

Water Bottle Rocket

The picture above is of Rachel and my whole rocket, including the cone and parachute. As you can see by the picture, we made the cone by folding paper into a cone shape and taping it up for durability. The parachute was made out of a garbage bag, which we cut into a circle. We then poked four holes into the bag on opposite sides after putting tape on it first, so the string wouldn't rip the bag if anything happened to it. After tying the string through the holes, we threaded them back to the rocket, where we tied them around the neck of the bottle. When launching the rocket, we folded the parachute into the cone, and then put the extra string from the parachute into the bottle of the rocket, so they wouldn't get in the way or open prematurely. The rocket itself was made out of two two-liter bottles. We cut off a fourth of one of the bottle's bottoms, so we could fit the bottles together, since longer rockets work better. At the bottom of the rocket, we had four fins, which were made out of cardboard that we had cut into triangles and then taped up afterwards.


The picture on the left shows our two cones. The cone on the right was our original cone, but we had taped a rock into the top of the cone, and when we tried getting it out, ended up ripping the paper a bit. We had to leave the tape in there so we didn't have to make a new cone (we did anyway), but the tape ended up sticking to the parachute, so the parachute wouldn't work. We then made a new cone, which was, as you can see, taller and skinnier. The cone being skinnier was actually a good idea, because it didn't really fit on the bottle, so it came off a lot easier. We also didn't put any tape on the inside of the cone this time, so the parachute had an easier time coming out. The first time we used the new cone, the parachute came out easily and helped the rocket land easier. Our rocket was able to stay in the air for 9.1 seconds, which was still a lot better than I was hoping for. Unfortunately though, after that one launch, our parachute didn't work after that, which might have been because of the cone getting squished a bit, or because Rachel and I got worse and worse at folding the parachute and putting it into the cone.
However, besides our mishap with the cones, everything else worked out pretty fine. The fins didn't break off, which was a big relief, and they, along with the cone, stabilized the rocket when it was in the air, making it a lot less wobbly.

Rachel and I found that filling the bottom bottle of the rocket halfway was the optimal amount of water.  Too much water means that there is too much mass, so the rocket wouldn't launch very high. Funnily enough, if you don't have enough water, you get the same results. Our psi, when launching the rocket, was always somewhere between 60 and 80.

Some of the physics I learned was that one side of the rocket couldn't be too much heavier than the other side. If the bottom was too heavy compared to the top, then when launched, it would be really wobbly. I also learned that it was better to have a cone rather than not, especially when you have a parachute. If you use a cone, it also acts as an extra weight for the top of the rocket, but also makes the rocket more aerodynamic. Also, if you didn't use a cone when using a parachute, the parachute would just add drag to the rocket when launched, so it wouldn't launch as high, resulting in less time in the air for the rocket.

Overall, I had a lot of fun with this project. Rachel (she's the one on the right in the picture) and I worked well, and we are both really happy that our rocket didn't break, although the head of the rocket got dented every time it nose-dived into the ground. We're really happy with our nine seconds, and had a lot of fun while building our rocket and launching it.