Light an Optics Unit

For the last couple of weeks, we were learning about light,mirrors and lenses. One main idea was about refraction which is a change in direction due to a change in medium.

Key Ideas

• Path of Least Time: light will find the quickest route to an endpoint
• If there is one medium/material, the path of least time will be a straight line from start to finish.
• If there are two mediums/materials (2 velocities), the path of least time will be at the point that the medium changes which is ultimately refraction.

Snell's Law

This law allows us to find the straw's angle of refraction from air to water. As you can see from the picture above, the pencil looks like it's bending when it changes medium.

Air: index of refraction=1

Water: index of refraction=1.33

Magnetism

STANDARD 6.3

Explain how objects like the Earth and metals can be permanent or temporary magnets

To determine if a magnet is temporary or permanent, it has to do with domains=groups of aligned magnetic fields.

Permanent Magnetic Materials

All the domains or fields line up in these objects which make them permanently magnetic. Some of the most common permanent magnets are nickel, iron, and cobalt.

Ever wonder why the Earth is a magnet? Well, the core of the Earth consists of metals. As we all know, metals contain moving charges. This means that the Earth is pretty much a giant magnetic field.

Temporary Magnetic Materials

From our lab in class, we know that paperclips are temporarily magnetic. Why? Because once the domains are in the presence of an atom, they line up. Without it, the domains are scattered in different directions.

Non-Magnetic Materials

Last but not least we have non-magnetic materials. They do not have any magnetic domains. Unlike the first 2 examples, this material will do nothing in the presence of a magnetic.

Electrostatics

Big Question: How is electricity generated and employed to do useful work?

This past week, our class was introduced to electrostatics! In class, we experimented with a lemon battery and a Van de Graaf generator. Both of these experiments taught us about voltage, charge, affinity, and electrical potential energy.
REMEMBER!
-Protons NEVER move, only electrons
-Opposite charges attract (+)(-), Like charges repel (+)(+) and (-)(-)
-Through friction, we transfer charge
-If there is a neutral object, only attraction. Never repelling

As you can see in the picture above, we used a lemon battery to help us learn the lessons. The battery (lemon) had a neutral charge from the penny (-)and the zinc nail (+). We connected each lemon with wires. The wires would connect the lemons by touching the opposite charges (penny to zinc nail) or vice versa. Later, we were challenged to make an LED bulb light up. To do this, we needed a lot more materials! Once the voltage was at about 3, we connected the bulb to the circuit and it lit up! Why did this happen? We made the lemon "do work" with the acid chemical reaction within the lemon. The wires, pennies, and zinc nails helped us complete the electrical circuit.

This concept is used in our IPad batteries! An IPad is shaped because of the battery used to power it. The battery is made of lithium-polymer. When we charge our IPads, the ions move from the anode to the cathode. When the battery is dead and not charging, the ions move back to the anode again. If you didn't know already, ions are charged atoms which either gained or lost electrons. Hence, plugging in our electronics to "charge" them. The outlet acts like a mountain. There is a separation of positive and negative charges. The mountain only separates the charges. It does not contain stored energy.

As you can see, the charges run up or down the hill which is created from the attraction of opposite charged or the opposition of like charges. An IPad battery has charges or electric potential energy.This energy allows us to power up our IPads.

Projectile Motion

Big Question-What is a projectile? What is the general path of motion?

There are 3 different types of projectiles
1) When an object is dropped from being at rest.
2) When an object is thrown vertically upward.
3) When an object is thrown upward at an angle or horizontally.

When there is only gravity acting on an object, it is considered a projectile. In the diagram below, we drew out 4 Velocity v Time graphs. Remember now! The slope of a Velocity v Time graph is ALWAYS acceleration. As you can see, some of the graphs show that the ball is accelerating. The two x-component graphs have a constant slope and velocity. The two y-component graphs depict the ball slowing down until it reaches the highest position. Then, the ball accelerates down while speeding up.

During our post game analysis, we analyzed our graphs and found the slope of everyone's shot. our table worked together to find the average number of our slope and compared it to the class. We realized the the average slope of the entire class was 10.2. Sounds like a familiar number, right? That's because the gravitational pull on Earth is 10N/kg. Gravity was the only force acting on the basketball. This explains why when the ball travels upwards, the velocity slows down. The ball starts to speed up once it reaches the top of the y-axis as it travels downward!

Hover Disk-Centripetal Force Lab

Big Question #1-What does it mean to analyze forces in 2D?

Last semester, we studied forces primarily in 1D. This meant that the fores only had a x-component or a y-component. To start off the year, we are studying forces in 2D. The forces are no longer straight up and down but, at an angle. To make our life easier, we can break up the angle up into x-component and y-component. Forces are vectors! Meaning they have both magnitude and direction (which we learned last year.) To solve for the value of a 2D force, first we break up the direction into the x-component and y-component. Next, we solve for the magnitude of the x-component and y-component by using Trigonometry. (SOH CAH TOA) REMEMBER! THe components of the force can be positive OR negative. We had to find the value of the x-component and y-component separately to find the net force of x and y separately.

Big Question #2-How do forces cause objects to move in circles?

In our first lab of the year, we used a hover disk with a string attached to it. With the disk on, I would hold the string and spin the disk around me in a circular motion. Since there was a string, we know that tension force (Ft) plays a big part in the lab. The center pointing force AKA the centripetal force in this lab was the tension force. The disk continued to accelerate because its direction of motion was constantly changing even if the disk's speed wasn't changing. Later, Ms. Tye showed us that when we let go of the string while the disk is spinning in a circular motion, it ends up going in a straight line tangent to the circle after it's released because the force and velocity are perpendicular to each other!

Big Question #3-What does it mean to be in orbit? How do satellites orbit planets and how do plants orbit the Sun?

To be in orbit means to continually follow a curved path around an object. Like the hover disks, the satellites orbit the planets in the same style. As the string (Ft) acted as the centripetal force to the kick disk, satellites orbit planets due to the centripetal force of gravity. The gravity is centered towards the planet thus, causing the satellite to orbit. Likewise with planets that orbit the sun due to gravitation force as a centripetal force. If the sun suddenly vanished, the Earth and all the other planets will eventually fall out of orbit and continue traveling at a straight line just like the hover disk lab.

Newton's 3 Laws of Motion

Big Question #1-What gives rise to a change in motion?

The only thing that can change the motion of an object is a net (unbalanced) force acting on it. This is given by Newton's First Law of Motion, sometimes also called the Law of Inertia.

In the hover disk lab, we learned about Newton's 3rd Law of motion which states that forces are equal and opposite. With the fan underneath the hover disk, we eliminated friction. We used interaction and free body diagrams to record out diagrams to record our data.

Big Question #2-What is the relationship between mass, force, and acceleration?

Later we performed the fan cart lab. We performed 5 different trials using 5 different masses to collide the fan cart with the aluminum ring. With the help of LoggerPro to calculate our slope (acceleration), we concluded that F=ma. The fan cart helped us learn about Newton's 1st and 2nd Law

Overall, we learned that F=ma or Force=Mass X Acceleration. The net force acting on an object will cause acceleration.
 There are also about 6 different types of forces: gravitational, normal, friction, tension, spring, and buoyancy. Interaction and free body diagrams help us explain what's going on in the lab.

Real Life Connection-Jumping!

Newton's 3rd Law of motion is applied to jumping like in basketball. An athlete can jump higher off a solid surface because it opposes his body with as much force as he is able to generate, in contrast to sand or other unstable surface.

Impulse Lab

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

In this week's lab, we collided 2 aluminum rings. One ring was attached to a car and the other on a force probe stand. The rings help to slow down the collision so we could analyze the experiment better. We measured the velocity with the sonic probe.

Data

• Mass of cart=0.25g
• Velocity before collision=0.4833 m/s
• Velocity after collision=-0.4008 m/s
• Area under F v T graph=-0.2580 N/s
• Impulse=area under a F v T graph-->J=Ft OR
• Impulse=change in momentum (Kgm/s)-->J=P final-P initial

Big Question #2
Which ring will bend more? Red car or blue car?

After the lab, we crashed a red car with less mass and a blue car with more mass. Aluminum rings were attached to both of the cars.

The rings bend the SAME amount

In any collision, no matter what the mass, there is an equal and opposite force! Since the red car has less mass, there is a greater change in momentum. Force and time are inversely proportional (increase T, decrease F) but impulse remains constant.

J     =      F      x      T 

(NxS)    (N)          (s)

(Kgm/s) (Kgm/s)  (Kgm/s)

Real Life Connection-Landing in Basketball!

When Michael Jordan goes for a dunk, he later bends his knees when he lands. By bending his knees, it increases the time of him landing which decreases the amount of force created from the force of the floor on his knees. There is an equal and opposite force on his knees and the floor. The impulse will always stay constant.