Light and Optics

During the  past week of physics we have been learning about how we see objects because light rays enter our eyes after bouncing off other surfaces. We also learned how that light behaves in a very predictable pattern. The picture below is a basic summary of what we did in class and it also helps describes the basics to reflection. 








































When you look at yourself in a mirror, whether its convex or concave( curved inwards or outwards), what you see is the image that's produced when light bounces off of your face, off of the mirror, and comes back to you. If you're looking into a flat mirror, the light will come straight back to you without bending at all. But a curved mirror will bend the light differently. 

When the light bounces off of your face and then off of a curved mirror, it won't come straight back at you, but will go off at an angle. For example if you bounced a ball off of the ground it it would come straight back but if you did it at an angle - it wouldn't come straight back at you; it would go off at the same angle as it hit the ground. That is part of the reason why when you look at a concave mirror, your image is upside down.

 The reason you end up looking upside-down on  concave mirrors  is that the mirror bends inwards so much that bottom of the mirror ends up pointed towards your forehead and the top of the mirror ends up pointed towards your chin or your neck! This means the image you see reflected is bent and unusual too. Your chin or neck is reflected at the bottom and your forehead is reflected at the top and there you go,you’re upside down!

Magnetism

Standard 6.1: How is electricity generated by moving magnetic fields? Provide an example.

Electricity generation is based on the principle of electromagnetism, a scientific law that was discovered by British scientist Michael Faraday and American scientist Joseph Henry. The principle states that when an electric conductor, such as a copper wire, is moved through a magnetic field, an electric current will flow through the conductor.Faraday and Henry found that a moving magnet (kinetic energy)  can generate an electric current which can be transformed in to electric potential energy.

For example when a copper wire passes through a magnetic field (anywhere near a magnet) the coppers electrons all start moving in the same direction. This will be one of two directions, depending on which end of the magnet is closer. As the magnet goes by the wire, electrons are attracted by the magnet and flow down the copper wire,  creating electrical power. Say we only one side of the magnet goes by the copper wire over and over, these electrons will only move in one direction. This form of power is called direct current (Electrons are flowing only one way). If the magnet rotates, the electrons will move in both directions. This is what you get from your wall and is called Alternating current (AC). Tesla is the man responsible for this concept and much of the modern power systems.

This is an example of an Alternating Current

In our world today there are many generators that use this idea of kinetic to electric potential energy such as a Fossil Fuel Generator. A fossil fuel generator produces electricity by burning coal in a boiler to heat water in order to produce steam. This steam is then built up in order to create a tremendous amount of pressure that will flow into a turbine which spins a generator to produce electricity. After the steam is then cooled, condensed back into water, and returned to the boiler to start the process all over again.

Fossil Fuel Generator

Voltage

During class this week, we started our unit on Electricity. We learned about voltage, charges, electric potential energy, and  Van de Graff Generator. We also conducted a Lemon Battery Lab which helped us understand how the flow of electrons generates energy to power certain devices like the Ipad.

The picture below is the battery for an Ipad. The ipad consists of a Lithium ion battery which allows the  the device to be more efficient and last longer. This battery has helped Ipad draw in many consumers and satisfy many customers with the long lasting battery. Little do customers know though is how it works. 

The lithium ion battery has a positive and negative side just like any battery and since we know that lithium atoms can gain and lose electrons, it is safe to assume that there is a steady flow of energy or Electric potential energy being experienced. Just like in class, the charges are going up a hill and moving from the positive side of the battery to the negative side creating a reaction which results in  electric potential energy. Charges cannot do this alone though they need voltage in order to move from one place to another. In essence, that is why we plug in chargers to recharge our batteries. You would think that the chargers add charges,  hence the name, but it actually does not.  Chargers add voltage and allow a reverse flow of charges creating the same reaction as before to make electric potential energy, moving the charges from negative to positive now.

http://electronics.howstuffworks.com/everyday-tech/lithium-ion-battery1.htm

Forces in 2D

BIG QUESTIONS:

1. What does it mean to analyze forces in 2D? 

In 2D, analyzing forces means breaking up the forces into two dimensions: an X-component and a Y-component. Next we have to solve for the x and y components using Sine( to solve for Y) or Cosine( to solve for X) also known as SOH CAH. Lastly we solve for the net force for the x and y components by adding up both all the x components and y components SEPARATELY.


Lab:
In a few of our practice problems during class we solved for the x and y components just like in the picture below. Once we solved for the x and y components we added all of them up to calculate the Fnet-x and Fnet-y. During these practice problems I learned that the x and y components can be negative or positive depending on what direction they are going in.


Reminder: 
- When solving for the x and y components remember they are vectors so they can be POSITIVE and NEGATIVE lines
-In a 2D problem we are dealing with TWO FORCES so we have to solve for both of them SEPARATELY

2. How do forces cause objects to move in a circle? 

During the hover disc lab, we swung the disc around in a circle making ourselves the center and applied a centripetal force using a rope. Centripetal force is a force that is necessary to keep an object moving in a curved path and is a force directed inward toward the center of rotation. This means that the hover disc is accelerating at a constant speed, but in a different direction. If we were to let go of the rope, the hover disc went in a straight line tangent to the previous circle it was moving in. To help explain why this happens we refer back to Newton's First Law: an object will stay at rest or keep moving at a constant speed unless there is a net force applied.

3. What does it mean to be in orbit? How do satellites orbit planets and how do planets orbit the sun? 

To be in orbit means to travel in a circular path around another. The satellites orbit planets with the same idea as the hover disc, centripetal force. The satellite is being pulled toward the Earth just like in the hover disc lab. The Earth is the center of this circle and the satellite is circling or orbiting around it. Same thing goes for the planets, the planets are orbiting the sun just like how the satellite orbits earth and how the hover disc orbited us except on a bigger scale. The sun is applying a centripetal force on the earth to keep it moving in a circular path and not crash into other planets. Now if the sun were to disappear the Earth and every other planet orbiting it would travel in a straight line tangent to the previous circle it was traveling in.

This picture illustrates the circular path that the planets travel in around the sun or how the planets orbit the sun.

Newton's Laws of Motion

Over the last week or two, our class covered all Three of Newton's Laws of Motion. We learned about his laws by performing two in class labs, doing a ton of practice problems, and from in class notes.

Our first lab was the HOVER DISC lab. In this lab we went down into the  gym foyer and performed several different scenarios using a hover disc. In groups of three we looked at these different scenarios to see what kind of forces  were taking effect. The picture below is an example of what my group and I did in the gym foyer. Also the two diagrams are the forces taking effect in this specific scenario. This lab allowed us to examine Newton's Third Law of Motion. This law states that when two objects interact, they exert equal and opposite forces on each other.

Interaction Diagram
   An interaction diagram, like the one below, allows us to analyze ALL the force on MANY objects. For example Person 2 is pushing the disc, meaning that Fn( Normal force) is taking place and there is Fg( Gravitational Force) between the disc, person 2, person 1, and the Earth.

Free Body Diagram
  A free body diagram, like the one beneath the interaction diagram, allows us to take analyze ALL forces on ONE object. In this free body diagram we are looking more closely at the disc and the types of forces being applied on it. A free body diagram allows us to show the magnitude and direction of the forces being applied, which really helps when your trying to solve an acceleration problem.

After we performed another lab, a Fan Cart Lab. In this lab our goal was to find the relationship between mass, acceleration, and force. We did this by turning on  a Fan Cart and letting it hit against a piece of aluminum on a force probe in order to get a constant force of about 2N( newtons). 

Next we used the logger pro program on the computer to get a time vs velocity graph. This graph gave us the slope of the change in velocity over the change in time which happens to be acceleration. 

Then we added a series of weights on the fan cart to help us find the relationship between acceleration and mass. We realized that mass and acceleration are  inversely proportional then we asked ourselves " what if we multiplied these mass and acceleration together," so we tried it out.

 Once we multiplied them together we were shocked to find out that it equaled the constant force we got during the beginning of the lab which as 2N. This helped us derive and equation the relates mass, acceleration, and force which is:

Force = (mass) (acceleration)

Later as we took notes in class, we found out that the equation above is also Newton's Second Law of Motion.  We can also understand Newton's First law of Motion by looking back at both of these labs. His first law states that an object at rest or traveling at a constant speed will continue to do so, unless a net force acts on it. Now just to recap everything we learned and sum it up,the picture below describes all three of Newton's Laws of Motion.

~Real World Connection~

A real world situation where all three of Newton's Laws take place could be a soccer game.

Newton's First Law of Motion:  A soccer player could kick a ball and it will keep going straight unless another player hits it or the friction between the ball and the earth reduces the ball's acceleration.

Newton's Second Law: Just kicking the ball itself could be an example for this law but to make things interesting soccer could also demonstrate how mass and acceleration are inversely proportional. If it were to rain the soccer ball would get heavier( increase in mass) making it harder for a soccer player to kick the ball farther or faster (decrease in acceleration)

Newton's Third Law: If a soccer ball hits a soccer player they would both exert the same but opposite amount of force. The reason why the ball bounces off the soccer player though is due to the difference in mass between the two.

Impulse Lab

BIG QUESTION:
What is the relationship between impulse, force, and time in a collision?

 Newton once claimed that  " For every force there is an equal opposite of force."

Lab:

In this lab we made a collision between a sonic probe and a cart, both with an aluminum ring attached to help us see how time manipulates force.

After we collected our data we found out that the change in both force and momentum( Impulse)  were relatively close. We got this by finding the change in momentum and also by finding the area of a force x time graph. As you can see in the picture below J ( impulse) =-.319 is pretty close the area of the graph T(F)= -.3768.

Because these two are really close ato being the same data this means that a force x times graph  represents the impulse .

The next part of our lab we observed a collision between two carts, one weighing more than the other ( blue cart weighing more) . We later found out that these two carts both bent the same amount even though one cart( the blue cart) weighed more. Now you can conclude that  NO MATTER WHAT THE MASS THERE IS AN EQUAL  AND OPPOSITE FORCE.  

Recently Asked Questions:

Why does the red cart fly back farther than the blue cart?

• The red cart flies back due fact that the blue cart has a bigger mass which means there will be a bigger difference in momentum between the red and blue cart.
• The aluminum rings doesn't affect why the red cart flies back because it doesn't change and it will have the same amount of force as the blue cart

Why do both the aluminum rings bend the same amount?

• They bend the same amount because the only thing that changed was the mass which doesn't affect the force or time in this situation

Real Life Connection

Rock climbing is the best way to think about an impulse lab for me. In rock climbing when a climber comes down a cliff, they use a rope to help INCREASE the amount of stopping time  and DECREASE the amount of force. This is a really big deal to climbers because if they couldn't increase the amount of stopping time then the force could be great enough to kill them. I think climbers really appreciate physics every time the choose to go climb.

Collisions Lab

Big Questions:
1. What is the difference between the amount of energy lost in an Elastic vs. Inelastic collision?
2. What is a better conserved quantity? Momentum or energy?


In this week's lab, our main goal was to try and find out whether momentum or energy is better conserved and why. We started this lab by doing an elastic and inelastic collision to see how momentum and kinetic energy changed.   

First we did an inelastic collision. An inelastic collision is when one object collides with another and they both travel in the same direction. After we performed an elastic collision. An elastic collision is when to objects collide and they both travel in two separate directions. During both these collisions we used a sonic range finder that measures sound so we could find the velocity before and after the collision.

Once we collected all our data, we then figured out the percent difference which is the change in energy or momentum. Looking at the percent differences of both inelastic and elastic collisions, made us realize that momentum has a lower percent difference, meaning that momentum is better conserved during any collision no matter elastic or inelastic.

Inelastic Collision's Percent Difference

Elastic Collision's Percent Difference

Real World Connection
 A good real life connection would be golf. Golf is a well known sport and is watched by tons of people around the world. This would be a great example for an elastic collision. During golf the golf club hits a golf ball, energy is then transfered from golf club to the ball. In the process though the ball loses some energy due to factors such as wind.