Light and Optics

We learned about light and optics this week and understand that light also bends.  The key idea is that light follows the path of least time.  The path of least time is traveling from one medium to another and the path is bent.  This bent path is known as refraction.  When light passes through a medium and changes its path it undergoes refraction.  For every object that light projects at there is a reflection ray that follows as well. To measure the refraction of light we use Snells Law: n1(sin1)=n2(sin2).  N1 stands for the initial material from index of refraction.  Sin1 stands for the measured angle from the initial ray.  N2 stands for the index of refraction for the 2nd material.  Finally sin2 stands for the measure of angle from the refracted ray. 

Magnetism

First what I learned was that magnets and metals have charges or electrons.  The big idea is that Moving Charges Create Magnetic Fields.  The earth also has this kind of reaction within it.  Withing the outer and inner core of the earth there is a lot of metals.  All of these metals are being melted by the outer core and when heated move faster.  Due to the movement of the charges it creates magnetic fields.  This magnetic field starts at the south side of the earth and comes up to the north side of the earth.  The way to determine which way the current went was with the right hand rule.  By placing your thumb in the direction of the current with your fingers out.  Then you have to curl your fingers above the wire as well as below the wire.  If your fingers are pointed away from you and your palm is facing the page then current is traveling away from you.  If your fingers are pointed towards you and your palm does not face the page then the current is coming toward you.

Electricity

Lemon Lab:
In this unit we learned about electricity which had to deal with voltage and charge.  Voltage is to electricity as  height is to gravitational potential energy.  Electric potential is voltage and electric potential energy is the charge times the voltage.  What we learned is that the higher the voltage, the higher the charge equals a greater electric potential energy.  In our lab we made a lemon battery that charged an led light.  Basically we used the lemon as a battery to produce the voltage and copper pennies inside of the lemon.  We then transferred the charge through alligator wires onto the pennies to the side of the led light.  The led light converted the electric potential energy and lit up with light.

Class Connection:
For our IPads it uses an internal rechargeable lithium-ion polymer battery.  The voltage varies from about 2.7V to about 4.23V (when fully charged.) The battery is claimed to provide 10 hours of video and 140 hours of audio playback.  As a lot of people know the ipad cannot be charged with an iphone charger even though they look a lot similar.  This is because it requires 2 amps using the included 10W USB power adapter and a USB cord with a USB connector at one end and a 30 pin dock collector at the other.  That means that the iphone charger is too weak to charge the ipad battery because of its low voltage. 

Projectile Motion

This week in our lab we learned about projectile motion which is analyzing an object in motion.  An important fact is that the object while in the air is only pushed by  a force of gravity called parabolic trajectory.

   In class we went down to the basketball gym and took videos of us shooting in the baskets with our Vernier Video Physics App.  There we then plotted our points and analyzed our data of the video we took.  From our data we then made graphs to show the direction of the x and y components over time and velocity over time.  In determining the data we found the equation is y=mx+b. Y stands for the acceleration, m is slope also velocity, and x is time.

This is a picture of our x component graphs.  The top picture shows the x component of the object over time.  Change of time over change of position equals slope and also the velocity.  Here we concluded that the slope was constant and same for the velocity.  The bottom graph is x velocity over time which equals acceleration.  Because the slope is 0, there is no acceleration on the x component.

This is a picture of our y component graphs.  The top graph shows the y position over time.  Here the change of time and change of position is not constant which means that it accelerates.  In the bottom graph the y velocity time over velocity crosses over the x axis.  This makes the y values become negative for the x values thus showing it has reached it's top height to which it goes down due to gravity.

Forces in 2D and Circular Motion

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

   What we think two dimension is flat and pixelated.  To analyze forces in 2D we must measure the x and the y components in a diagonal line.  When we split the x and the y they are defined as two dimensions.  To calculate these two dimensions we use sin, cos, and tangent.  With that we can determine the Fnet for the x and the y.


2. How do forces cause objects to move in a circle?
  In class we had a hover disk attached to a string and circled it around us.  This force we used to pull the hover disk toward us is called centripetal force.  As we are pulling the hover disk there is acceleration, but it is at a constant speed and accelerates through changing directions.

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

  To be in orbit means to constantly circling something.  Just like in the hover disk, satellites are pulled through centripetal force circling the planet in gravity.  Planets orbit the sun through a centripetal force of gravity and the satellites orbit the planets.  If the sun was not there scientists say that our planet would go out of orbit and randomly fly off into space.

Impulse Lab

Big Question: What is the relationship between impulse, force, and time during a collision?

• The purpose of this lab was to understand momentum by using the relationship between impulse, force, and time in a collision.  We first pushed a cart with an aluminum loop into another aluminum loop on a force probe.  From there we conducted our data from the computer and measured the velocity of the cart before and after the collision.  With this information we can find the impulse witch is momentum before minus momentum after.  

• Momentum before(f): -.127
• Momentum after(i): .133
• Impulse: .3kg *m/s

Conclusion: We learned that impulse is a change in momentum in this lab.  Force is equal and opposite.  The time increases, the force decreases, and the impulse remains constant in a collision.  

Real World Connection:

   In tennis the players follow through when hitting the ball which is a collision between the racket and the ball.  The act of the serves increase the time which causes a change in momentum witch applies to impulse.  The force depends on how hard the player hits the ball.  By increasing the time on the swing it also increases the velocity which can determine how good your hit is.  

Collisions Lab

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

In our lab we first set up the two carts, each with a mass of .25kg. After connecting the two range finders to the laptop and matching each one up with the corresponding cart, we began collecting data.

After creating an Elastic Collision, and an Inelastic Collision, we measured the speed of each cart before and after the collision in m/s. Then we calculated the momentum (kg x m/s) and energy (J) of the carts before and after the collisions.

• We then had to collect all our data to get the exact amount of results. 

• This percentage lost in the inelastic collision.

• The percentage lost in the elastic collision.

In our inelastic collision, less energy was lost than in the elastic collision

We also understand that more momentum is conserved than energy because a lot more energy looses sound and friction. 

 

Real World Connections-

 

For a real world connection I think of when i'm playing basketball for collisions.  When I shoot the ball I am aiming for the backboard and the ball collides with it.  There is also momentum because the ball is moving toward at a certain velocity aswell.  When the basktetball collides with the backboard it will continue collide onto the gym floor until it is at rest.