Physics Class Review

Physics is all around us. I was surprised when I first started noticing concepts I learned in physics class pop up in every day life. It is the science that describes how our world works. I think physics is what moves us forward. It constantly helps us discover new idea and concepts that helps improve our way of life. So, I guess I would define physics as the study of how the world/universe behaves.

In all honesty, I really enjoyed the class. Sometimes, I even felt excited before class started to learn the new concepts. The class moved at a fast, but still comfortable pace for me. I always ended the day feeling like I had learned a lot but never really felt too overwhelmed. before I started the class, I wasn't looking forward to 4 or 7 hours a day in class 5 days a week, but after finishing the class, it feels like it passed by really fast. The classes were very hands-on and interesting, rather than listening to a teacher lecture and give out worksheets.

Now that I look back, I have learned A LOT of information that I had never even dreamed of knowing before this class. We began in Unit 1 which was basically an introduction to physics. Our major focus in Unit 1 was to learn how to analyze and collect data from labs and experiments. We learned a lot about graphing and graph relationships, as well as scientific notation and SI units. Unit 2 is the start of kinematics. Kinematics is the study of motion. We focused on different types of quantities, scalar and vector, like distance, displacement, speed and velocity. We also learned the three main graphing rules for d/t graphs and v/t graphs and how to analyze them. This lesson taught us a lot about interpreting motion through words. Then, in Unit 3 we began uniform acceleration. This lesson is basically like what the title describes it to be. Acceleration is change in velocity/unit of time or m/s over s or m/s^2. Then we learned the relationship between d/t graphs, v/t graphs and a/t graphs. Acceleration is a curved distance vs. time graph and a sloped velocity vs. time graph. We also learned the three kinematic equations, DAT, VAT and VAD (d=at^2+vot, v=vo+at, and v^2=vo^2+2ad). Another important thing we learned is how to organize solving problems; we used the order of d, a, t, v, vo for the givens. Next, in Unit 4 we began projectile motion. One important idea to remember is that axes are independent. We learned that when vertical and horizontal movement is combined, it creates a parabolic motion. This is the unit with lots of word problems. We used trigonometry, like sine, cosine and tangent, to solve some of the problems. Unit 5, we did forces in equilibrium. In this unit we learned a lot about forces and how they act upon each other and other objects. Most importantly we learned the bureku technique, taught by Mr. Blake himself! We also used trigonometry in this unit to solve the diagonal problems we encountered. The bureku technique taught us to break up any diagonal into x and y vectors, and then use trigonometry on the right triangle you just created. We also learned Newton's three laws. The first law is the law of inertia, the second is the law of acceleration and the third law, is the action-reaction law. We also learned that one Newton (N) = kg*m/s^2 and weight = mg. An important thing to remember is that a normal force is the force perpendicular to the surface. This unit focused a lot on balanced and unbalanced forces. In Unit 6, we focused on friction. There are two main types of friction, static friction and kinetic friction. Force of friction is represented like this Ff which is equal to the M*N. Next, in Unit 7, we learned about momentum. Momentum (p) is mass (m) x velocity (v). The units for momentum is kg x m/s. The law of Conservation of Momentum is: In a closed system, momentum of a system is always conserved. Force = change in p/ change in t. The change in p is the force x time or the Impulse. Also, the pfinal - pintial = F x change in time. We learned concepts on how momentum is always conserved and elastic and inelastic collisions. Then, in Unit 8 we learned all about work and energy. The Law of conservation of mass is: Energy cannot be created or destroyed, it can only change forms. With this in mind, we learned different types of energy, kinetic and potential, and how to find the work. There is also spring potential energy which deals with energy of springs. We also learned some graphing rules with force vs. distance graphs. power is the rate at which work is done. The units for power is joules/sec or watts. In Unit 9, we work on waves, YAY! We determine the difference between transverse and longitudinal waves, we see how medium affects waves, and find the relationship between velocity and frequency and wavelength. We learn superposition and how waves interfere, as well as resonance and pitch. Unit 10 we learn the speed of light, which is 3x10^8 and the difference between sound an light waves. We learned opaque and transparent, and the whole spectrum of electromagnetic waves, from low frequency things like radios, to high frequency light like ultraviolet, and x-rays and gamma rays. Specular is a smooth surface and diffuse is a bumpy surface. White light is a light with all frequencies of light, ROYGBIV. We learned how to mix light colors and that objects reflect certain colors and absorb others.

I really liked this class because Mr. Blake made it a very hands-on and interactive class. I am a very visual and hands-on person, so when I get to experience the concepts of physics first hand, I really understand the concepts better and it is WAY more enjoyable for me. I liked the review sessions we had because it touched up on very important things and allowed me to ask questions that I never thought of before. It was great that they were right before the test. I also liked that Mr. Blake gave us progress reports because it let me know how I was doing in the class. I know I said that visual learning and hands-on experiences were important to me, but so was the packet. The packet was very useful for practice problems and when I needed to look back for a quick review or look back what we did. I sincerely enjoyed the class a lot more than I thought. I took this class to find out if I would be interested in these types of sciences, and I certainly am! I look forward to maybe pursuing more of this interest.

Something the class could improve on was having more field trips to places outside of Punahou. Also, I think it would be fun if we had more projects to do instead of tests, wink wink.

Thank you Mr. Blake for being so helpful. You really did make learning fun and interesting with your jokes. Your interactiveness and fun personality made it easy for me to ask questions and really get into physics, thanks! Kamehameha is really lucky to have you.

Unit 10: Light Properties (refraction)

Today was all about refraction. Refraction id the bending in waves due to change in media. For example, when light shines through a pool, the light doesn't shine in a straight beam, it looks like its bent. This is refraction because it bends form the change in the material the light is in. One major rule for refraction is that when moving from a fast medium to a slower medium, light will bend toward the normal. The normal is the force perpendicular to the surface.

In the picture above, the laser is moving through a fast medium at first, then the medium changes to a slower medium, causing the laser to bend. Then the laser moves back into a the faster medium again and is going at the same velocity and angle as it was before. As you can see, the laser wanted to continue going in the same direction after hitting the different medium, represented by the dotted green line, but the laser bends in the slower medium toward the normal (N) force, which is represented by the dashed blue line.

Different colors bend at different rates. Red bends less and blue bends more.

Another important rule to remember is Snell's Law which is: n1sinθ1 = n2sinθ2. "n" is the index of refraction, which is a ratio, so there are no fractions. n = c/v. "c" is the speed of light in a vacuum, and "v" is the speed of light in the medium. Here are some common ones:

nvacuum = 1

nair ≈ 1

nH2O = 1.33

nglass = 1.5

ndiamond = 2.42

All angles are relative to the normal. When the light is moving from a fast medium to slow medium, the light bends toward the normal, whereas when the light moves from a slow medium to a fast medium then the light bends away from the normal.

We also learned about lenses. Lenses can be either concave or convex. When light goes through either of them, the image created can either be real or virtual, inverted or right-side up, and reduced or enlarged.

In the picture above, I am holding up paper and a magnifying glass because in class we used convex lenses to create a focal point with the sun's light and burn paper. That is why the paper I am holding up has holes in it.

hehehe.

Unit 10: Light properties (reflection)

Today we learned a lot about reflection. The two main types of reflection are specular reflection and diffuse reflection. Specular is when the surface is relatively smooth compared to the wavelength of the wave. Diffuse is when the surface of the object is bumpy/rough when compare to the wavelength of the wave. This means when light reflects off of a specular object, the light reflects off of a mirror-like object in a single direction and when light reflects off of a diffuse object, the light reflects in all different directions. This is because of the law of reflection. The law of reflection states that the angle of incidence is equal to the angle of of reflection, relative to the normal. The normal is a force perpendicular to the surface, so when the surface is smooth, there is on normal, but when the surface is bumpy there are many different normals, and therefore many different directions the light is reflected.

Today we also did a lot of work on color and color mixing. This is not the same type of color mixing you do in art class, because that is with pigments. This type of color mixing is using light. here is the basic color chart to follow.

Complimentary colors (colors on oppos. sides) create white.

White light is light with all of the frequencies or, in other words, ROYGBIV. Objects reflect certain colros and absorb certain colors. For example, a blue shirt that you own is blue because the shirt was made to absorb all of the other colors and reflect blue. When there is a shadow, there is an absence of light because all of the colors are absorbed and therefore it is black. That is why, when you wear a white shirt, you reflect all of the colors, but when you wear black, you feel hotter because it absorbs all of the colors.

 Here are two pictures (above and below) of when we used blue, red and green projectors in class to mix the lights and make shadows. The picture above is of Mr. Blake and the picture below is of me.

The picture below is when we used lasers to experience how light reflects. You can only see the beams if the air is junk, so we sprayed stuff in the air so that we could see the laser beams. cool.

Extra Credit - Parents Show and Tell

Me and my dad :)

Unit 10: Light and Color

Today we learned about light and color.In the last unit we learned that sound is a pressure wave, but in this unit we learn about light and that it is a electromagnetic wave. The electromagnetic spectrum is a range of all electro magnetic waves. Electro magnetic waves are transversal waves that are perpendicular to each other. Some things we have to know before I talk about the range, are vocabulary. Opaque means light cannot pass through and transparent is when waves can go through.

The lowest frequencies in the spectrum are radios, TVs and cellphone. Theses range anywhere from 500 KHz to 1000 KHz. Next level is microwaves. The frequency of microwaves is the resonance of water. The next level is infrared. Infrared literally means "below red". Infrared light is heat energy and radiation. This is used to sometimes detect people through walls for police. Then comes the visible spectrum, which means the RAINBOW! This includes ROYGBIV. The only light visible to humans is between 4x10^14 to 7x10^14 Hz. Red starting as the lowest frequency and longer wavelengths to violet, which is higher frequency with shorter wavelengths. red has the lower energy while violet has higher energy. After visible frequencies is the ultraviolet (above violet). This is also known as UV and has different types like UVA and UVB and this is given off by the sun. Ultraviolet is opaque to the ozone layer and glass. And finally, the highest frequencies are X- rays and gamma - rays. These can go through just about everything except bones.

As you can see in the picture above, I use Neutrogena sunblock with SPF 55 when I go out and play tennis. I use it mostly because it smells better than other sunblocks and isn't oily but that is besides the point. The main purpose for this is to protect my skin. Luckily for me I have a higher melanin in my skin because I don't burn as much, I just get really tan. Like it says on the bottle, it has UVA and UVB protection. The main use for sunblock is to literally block the sun. It makes your skin more opaque to ultraviolet light. COOL.

Unit 9: Sound and Waves continued

In continuation of unit 9 we learned more about sounds and waves. Sound is the longitudinal wave from vibrations. We learned the range of sound for humans. Humans range of hearing usually is around 20Hz to 20,000Hz. Ultrasonic sounds, sounds that are over 20,000Hz are very high pitched and are what bats and dogs hear. In fact, bats use ultrasonic sounds to communicate. Infrasonic sounds are sounds that are below 20 Hz and are used by elephants to communicate. These types of sounds are so low pitched that we can't hear it. That is why animals can sense things happening, like natural disasters, before they actually happen. So, if I ever see my dog going nuts, I will run for my life (I'm just being dramatic).

We also learned that refraction is the bending of waves due to the change in medium and reflection is the bouncing of waves. Resonance is the building up of energy and dispersion is the spreading of waves. we also learned that sound travels fastest in solids, next fastest in liquids and slowest in gases.

In class, we did a lab using tuning forks. We filled a graduated cylinder with water and had a tube inside. We then jolted the tuning fork so that it would begin to vibrate. Then we held the fork over the tube while moving the tube up and down to find the perfect length of 1/4 of a wave. Each tuning fork has a specific note that it makes when vibrating. After finding the 1/4 of a wave we multiplied it by four to find the length of one whole wave.

In the picture above, I am making music with the wine glass with water in it. I am making the glass vibrate so that it creates a sound with different pitches depending on how full the glass is of water. Pich is the frequency of sound Unfortunately, I just lied to you because the wine glass in the picture is made out of crystal and doesn't have the same effect.

Unit 9: Waves and Sound

Today we learned all about waves and sound for unit 9. We learned that a wiggle in time is vibration and a wiggle in time and space is a wave. So when you are "waving" to some one, you cannot be standing still because that wouldn't be waving, it would be vibrating. Here is a diagram of what we learned about waves:

One whole waves length includes the up loop and the down loop. It is measured from two identical places in the wave. The crest is the top of a wave and the tough is the bottom of a wave. The dotted line is where the wave is at equilibrium. A wave is just an energy flowing through a medium. A medium is the material the wave is in. Wave length can be represented by a lambda symbol.

Amplitude is the distance from equilibrium point to highest/lowest point in the wave. Period (T) is the time is takes for one whole cycle to occur and frequency (f) is how many cycles pass in a second. the unit for frequency is Hertz (Hz) or 1/sec. An equation for this is T= 1/f. Also to fin the velocity of a wave, you use the equation v = wavelength x frequency. Wavelength and frequency are inversely related. Only tension and medium affect the velocity, but the wavelength and period are directly related.

A transeverse wave is wave energy that moves perpendicular to wave velocity. A longitudinal wave is wave energy that moves parallel to wave velocity.

In this picture I am blowing a whistle. This is a rape whistle so it makes a very loud and high pitched noise. It is very high pitched because it has a really high frequency.

Water Bottle Rocket Analysis

Our rocket included, two 2-liter bottles, card stock for the cone, duct tape, cardboard for the fins, and string and a plastic bag for the parachute. Then we named the rocket Rocky Jr. and wrote its name on the side for some flare. We first cut the bottom of one of the bottles and attached the open side to the bottom of the other bottle with a hot glue gun and duct tape. This way, there were openings on either side. Next we cut out four fins from cardboard and then glued and taped them on evenly spaced. Next, to add more time to our launch, we cut out a circle from a trash bag and then cut four small holes on the edges of the circle to tie string in. We then tied the other ends of the four pieces of string to the bottle's neck. Also, we took the card stock and formed a cone and used duct tape to make it sturdier. We taped a rock to the inside tip of the cone to add weight.

The picture above is what we started with today. At the start of class, both Joy and I took out our rocket to launch. We launched about three times and could not get up to 7 seconds. We knew it was because we needed our parachute to come out, because all three tries the parachute didn't come out and our rocket nosedived to the ground even when we tried to adjust the position of the nosecone. Each time the launches squished the nosecone even more. After the third try, we decided to take the rocket back in and redo the nosecone because the it was squished and the parachute wasn't deploying.

After watching other groups succeed at deploying their rockets we decided to try a new approach to our nosecone. Instead of adding weight to the tip, we tossed the rock-at-the-tip idea and when for a more lightweight approach. We used the same card stock paper, and a lighter tape. Also, I left a small 3mm hole at the tip of the cone because the groups that succeeded used a funnel, which has a hole at the tip.

Then we went out again to launch some more and the first try we got 9.1 seconds!!!!! YAY! The cone fell off and the parachute deployed. We found it worked best with the bottle filled about halfway and pumped to 60 to 80 psi. Not only did our bottle go very high, which it usually did, but the rocket also came down a lot slower with the parachute.

But, after the first launch, the next couple of launches did not do as well. Either the parachute did not deploy or the launcher fell sideways. I think it might be because after the first time, the cone was still a little beat up.

I learned that there needs to be balanced mass on either side of the rocket but also not TOO much mass because then it will weight too much and won't accelerate. Also, its better when weight is distributed evenly and for the rocket to be longer because then it will be more stable. The closer the fins were to the back of the rocket, the farther back the center of gravity would be which makes it more stable. When there was around 60-80 psi, the rocket had just enough pressure to shoot, but not too much where it would explode. I also learned to be persistent because we kept trying over and over again until we got it right and until we could no longer launch our rocket. Also, I learned that sometimes watching others succeed can help you succeed too.

Overall, I am really happy that our rocket was pretty sturdy and well built because even though our rocket hit the ground hard almost every time, the fins, bottles, tape and parachute all stayed perfectly intact. YAY!

Here is Joy and I with Rocky the rocket.
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Water Bottle Rocket Engineering

The picture above is the finished product. Our rocket is made up of two 2-liter bottles, card stock for the cone, duct tape, cardboard for the fins, and string and a plastic bag for the parachute. Then we named the rocket Rocky Jr. and wrote its name on the side for some flare. We first cut the bottom of one of the bottles and attached the open side to the bottom of the other bottle with a hot glue gun and duct tape. This way, there were openings on either side. Next we cut out four fins from cardboard and then glued and taped them on evenly spaced.

Our rocket unexpectedly did better than we thought when we tested it without the parachute and cone. Both times we shot the rocket we got over 6 seconds. We found it worked best with the bottle filled about halfway and pumped to 60 to 80 psi. The went pretty straight up and only swiveled a bit, but I expect that is from the lack of weight on the tip of out rocket.

To fix that and to add more time to our launch, we cut out a circle from a trash bag and then cut four small holes on the edges of the circle to tie string in. We then tied the other ends of the four pieces of string to the bottle's neck. Also, we took the card stock and formed a cone and used duct tape to make it sturdier. We taped a rock to the inside tip of the cone to add weight.

At one point, we thought of cutting off the top of the connected water bottle to add the rock to the inside of the water bottle and then tape it back on. We not only found out that it is really hard to tape or glue the water bottle top back on, but it is also not a good idea to put the rock inside the bottle because after adding the cone, the weight would be closer to the center of the rocket, which is not good.

We hope tomorrow, our parachute will deploy and the weight from the cone will add stability. We made the parachute strings long so hopefully that will work well. Tomorrow, we just have to figure out how to connect the cone to the bottle, but that won't be too hard.

Unit 8: Energy and Work Continued...

Today we continued learning and reviewing about energy and work. We also learned about power. Power is the rate at which work is done. Power is equal to the change in energy divided by the change of time or work over time. The units for power is Joules divided by seconds or watts (w). So, if you get a word problem containing force (N) and distance (m) and time (sec), you can find the power because Force x Distance equals work and then you can divide work by time. There are also many variations of the example that I just gave.

1.2.

3.4.

As you can see in the pictures above, a green object is falling from my desk to the ground. In the picture 1, the green object starts at the top of my desk and has gravitational potential energy. As it falls in pictures 2 and 3, the object loses gravitational potential energy and gains kinetic energy because gravitational potential energy and kinetic energy are inversely related. In picture 4, when the object is right about to hit the ground, the object has a kinetic energy equal to the original gravitational potential energy in picture 1.

Unit 8: Work and Energy

In this unit we focus a lot on energy and the different types of energy. There is Kinetic energy (KE), Potential energy (PEg) and Potential spring energy (PEs). As Kinetic energy increses, potential energy decreases, and vice versa. This shows that KE and PE are inversely related. We also learned the equations and how to find the different types of energy of an object.

KE = 0.5 x mass x (velocity)^2 = 0.5mv^2

PEg = mass x gravity x change in height = mgh

PEs = 0.5 x spring constant x (distance spring stretched or compressed)^2

The units for energy is newton meter or joules (J). Energy is a scalar quantity, which means it only has magnitude and not direction. Work is the change in energy or Force x Distance. We also learned a very important law, which is the Law of Conservation of Mass: Energy cannot be created or destroyed, it only changes forms.

In the picture above, I have potential energy because I am raised above the ground and the force of gravity is pulling on me.

In this picture, I am jumping off my couch and while I am in the air my kinetic energy is increasing while my potential energy is decreasing.

Egg Drop Lab

I think that our capsule will work because we have crumpled paper, stuffing and air to provide a cushioning from the impact. These will increase the contact time for the capsule, will therefore decrease the force.

For the Eggrop lab, Brent and I used a plastic bag, slightly crumpled recycled paper, a paper plate, two rocks, cardboard, a plastic cup (with a lid) and stuffing (like from a plushie). We crumpled up the paper so that it wasn't dense, but it had some spring in it. We took the cup and filled it with the stuffing so that the egg was packed snuggly in the cup when we closed the lid. We filled the plastic bag with air and the crumpled paper and then placed the cup resting on the top and then tied the plastic bag shut. On the bottom of the bag, there is a plate glued flat with rocks glued to the plate, and then another piece of cardboard glued and taped over the rocks and paper plate. Our capsule's dimensions were 22cm x 21cm x 29cm.

The paper cushioning inside the bag and the stuffing inside the cup work as a crumple zone for the capsule, which increases the contact time for the egg. Increasing the contact time will reduce the force the ground puts on the capsule because time and force are inversely related. The rocks are at the bottom to make sure the whole system falls upright. Even though this adds to the mass, which will ultimately make the capsule fall with more acceleration and the momentum, but it forces the whole system to fall in the position we intend it to fall. We used a paper plate so that it would be easier to secure the rocks to the bag and we put the cardboard over the rocks make the bottom flat so that when it does hit the ground, it doesn't roll to the side. The awkward shape of the capsule will also hopefully increase air resistance.

Here are two force diagrams, the first showing the capsule in free fall and the second diagram showing the capsule as it hits the ground. As you can see the capsule is condensed because of its crush zone. The forces acting upon the capsule in free fall is the weight of the capsule and the air resistance. Since the weight is more than the air resistance, the capsule is accelerating downward, except when the capsule reaches terminal velocity, then the capsule will have balanced forces and will not be accelerating. The second diagram shows the capsule as it hits the ground. The forces acting upon are its weight and the force of the ground. Since the capsule is coming to a sudden stop, it is accelerating in the opposite direction so the force from the ground is greater than the weight of the capsule.

Luckily, our capsule was very successful  it did just as we hoped. The capsule properly crumpled in the right places, fell upright and kept the egg safe. The paper cushioning inside the bag and the stuffing inside the cup work as a crumple zone for the capsule, which increases the contact time for the egg. Even though we were successful, we still could've done some things to make it better. I had the idea of twisting the bag as it fell to keep it even more stable. Also, I think we should've had a rock hanging from a string on the bottom instad of rocks just glued to the bottom to be even more stable.

Unit 7: Momentum, impulse and collisions

Today we worked more on momentum. We learned that momentum always wants to go in the same direction and stopping momentum takes more force. In the picture above we did a lab using the air track two carts, and a photogate to measure velocity. We used a nerf gun to hit the cart and push it through the photogate, so we could find the velocity of the whole system, which is the carts and the dart all together. From that we could find the cart/dart final velocity and total momentum. We coud also find the initial velocity for both the carts and the dart. To do this we used a series of equations, like Change in momentum is equal to force x time, which is equal to mass x change in velocity. This lab also helped us understand how momentum is conserved.

Today we also worked on word problems with impulse and collisions. The more mass an object has, not only does it has less acceleration, but the object will have less momentum. To reduce impulse (change in momentum), you have to decrease the contact time. We also learned that the area under the curve of a Force vs. TIme graph is the impulse.

Unit 7: Momentum, Impulse, and Collisions

Today we learned all about Momentum. Momentum (p) is a vector quantity and can be defined as mass times velocity. Its units are kg x m/s or kilograms-meters per second. The law of Conservation of Momentum (p) states that in a closed system, momentum of a system is always conserved, which pretty much means that momentum will not change over time in a system. We also learned about Impulse. Impulse is the change in momentum of the object or Force x Time. Therefore, force is equal to the change in momentum divided by the change in time, which makes Force and the change in time, inversely related.

The lab we did today used the air tracks and photogates once again. This time we attached rubber bands to the ends of each cart to study their collision. This type of collision is called, elastic collision. We used the photogates to detect the velocities of both carts before and after they collided and in different scenarios to understand collisions and momentum better. After collecting data, we used the different equations to find the total momentum for each cart in each scenario.

We also learned how airbags come out with a lot of force. That old lady showed him...