## Sunday, May 5, 2013

### Palm Pipe Lab

Big Questions:

How can we tell something (like sound) is a wave if it is invisible or too small for us to see?
How do musical instruments work?
What's the difference between a woodwind & a stringed instrument?

The Lab:
This week in Physics, we learned all about sound waves and harmonics.  We did a lab in which we analyzed closed end pipes that produced musical notes.

We started the lab by measuring the palm pipe's length and diameter.  We then used these measurements to find wavelength, frequency and ultimately, the musical note the pipe would produce.

Here are my calculations:

length of the pipe:  15.8 cm (.158 m)
diameter of the pipe: 1.4 cm (.014 m)

equations:

1)  Length= 1/4(wavelength) - 1/4(diameter)
.158 m = 1/4(wavelength) - 1/4(.014 m)
wavelength= .646 m

2)   Velocity= frequency x wavelength
343 m/s = frequency (.646 m)
frequency = 531 Hertz

I then plugged in this information to Wolfram Alpha and found out that my pipe produced the C5 note and 25 cents.  After everyone figured out their notes, as a class, we harmonized in playing Twinkle Twinkle Little Star.  Not going to lie, we were pretty darn good.  America's Got Talent worthy? I think yes!

Since everyone at our table had different size pipes, we figured out that the different lengths created different notes.  The longer the pipe, the lower the note and the shorter the pipe, the higher the note.  This is because, since only odd numbered harmonics can fit in closed end pipes, longer waves can fit in a longer pipe, therefore creating a lower note.

Real World Connection:
Learning about harmonics in class is really cool because music is something we listen to in our daily lives, and getting to relate something we love to something we learn in school is so cool.  It's awesome to actually understand how music is created!  Seeing how awesome we were at "Twinkle Twinkle Little Star" made me wonder if people play the "PVC Pipes," and guess what... THEY DO!  This video shows a guy playing "The Legend of Zelda" on his very own set of PVC pipes.  I bet if our class practiced enough, we could totally play bigger and better things than "Twinkle Twinkle" (not that it's not a classic).
By the way, this kid is great!

Imagine putting our whole class's pipes together and creating a complex PVC pipe instrument like this! It's all Physics!

## Sunday, February 10, 2013

The iPad battery is a great example of a real world application of the concepts we have been learning about in class this past week. The battery is a Lithium Polymer battery and it is used in various electronics that we use everyday such as cellphones, computers, and of course, the iPad.  These batteries are used because they can be shaped in different ways to fit into a specific space or position.  As we learned in class, the battery makes voltage and then turns that voltage into different types of energy that can be used as heat, sound and light.  The battery is also known as a lithium-ion battery, meaning that electrons and protons give it it's charge.  The charge and voltage create potential energy and forms a "mountain" which electrons and protons move up and down, turning this potential energy into sound, heat, light etc. that allows us to use electronics such as the iPad, in our daily lives.

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

## Monday, January 21, 2013

### Hover Disc Centripetal Force Lab

Big Questions:

How do forces cause objects to move in circles?

The force that makes objects move in a circle is centripetal force which means a "center-pointing" force.  In our hover disc lab, a rope was attached to the hover disc while a student moved it in a circular motion around them.  We learned that the hover disc is being pulled toward the center through a tension force (the rope).  Because it is moving at a constant speed, but also accelerating, it remains in a circle.  This was hard to understand at first because acceleration has always been "a change in speed," but in this lab we learned it could also mean a change in direction.  So even though the disc moves at a constant speed, it is simultaneously changing direction, causing acceleration.

What does it mean to analyze forces in 2D?

Up to this point, we have only worked with one dimensional forces, meaning forces in one straight line.  However, in this lab we are working with two dimensional forces, which means there is an x-axis and a y-axis.

What does it mean to be in orbit?

When an object orbits around another object, what it is really doing is moving in a circular motion around it.  An object stays in orbit, rather than just floating around because of centripetal force.

How do satellites orbit planets?

satellites are always falling.  The reason they are able to orbit around the earth and not fall and crash is because they move at a fast enough constant speed that allows centripetal force to keep it from falling.  We saw this in our lab.  When we were moving the hover disc in a circle, it had to be going fast enough to move at a constant speed and remain in a circle.  If it was moving too slowly, the centripetal force would not be able to keep it in a circle and it would "fall" towards the middle.

How do plates orbit the sun?

Planets orbit around the sun very similarly to how satellites orbit around the earth.  Each of the planets are "falling" but a centripetal force pulls them into the sun and keeps them moving in a circle around it.

## Sunday, November 18, 2012

### Newton's Three Laws

Purpose:
The purpose of the labs we have performed for the past 2 weeks was to discover Newton's three laws of motion.  These laws explain why things move the way we see everyday, by describing what types of force act on the object at all times.

Newton's Three Laws:

1) if an object is at rest or at a constant speed, it will remain that way unless it experiences a net force.

2) the amount that an object accelerates depends on the object's mass and the net force it experiences.

F= ma

3) Whenever two objects interact, they each exert an equal but opposite force on each other.
In other words, for every reaction there are two forces.  Those force pairs are: equal,
opposite and same type

Hover Disc Lab:

Big Question:

What gives rise to a change in motion?

Summary of Big Question:

Anything at rest or in constant motion feels the same net force.  It is the change in speed or direction that causes a change.
This expresses Newton's First Law of motion!

In this lab, we went to the gym to perform it.  When turned on, the hover disc almost completely eliminates friction with the ground.  We performed 10 trials, each with different scenarios, and recorded the different forces that we saw in interaction and free body diagrams diagrams.  Here are a few of them:

1. Hover disc is at rest; disc has not been pushed

2. Hover disc is OFF; disc is being pushed by person 1

The forces we learned about in class and few that were recognized in this lab (green/ first 3 listed) were:
• Gravitational - Fg - two objects have mass
• Normal - FN - electrons on the surface of atoms repel
• Friction - Ff - electrons on the surface of atoms are shared
• Tension - Ft - electromagnetic bonds are stretched (rope)
• Spring - Fs - electromagnetic bonds are stretched/compressed (spring)
• Buoyancy - F- fluid molecules repel on/in liquid

Fan Cart Lab:

Big Question:

"What is the relationship between mass, force and acceleration?"

Summary of big question:

• Acceleration (a) is a change in velocity over a change of time.  It can be found by taking the slope of a velocity/time graph or using the equation [(v2-v1)/t].

• In order for the force to remain constant, the mass and acceleration must be inversely proportional (when one is increasing, the other is decreasing)

• This lab expresses Newton's Second Law of motion!--> F= ma

To measure the constant force in this lab, we set the fan cart on it's highest setting and watched it accelerate down the track and hit the force probe.  To measure the acceleration, we added different brass masses every time to see how it differed. When it hit the force probe, the computer calculated the force and the acceleration of the fan cart.  Using
different masses each time, we performed 4 trials and
these were our results.

Because no experiment is 100% accurate, our percent differences were:
trial 1- 27%
trial 2- 22%
trial 3- 19%
trial 4- 10%

To give an idea of what the graphs on the computer looked like (notice the similarities and differences):

First trial (3kg)

Last Trial (8kg)

Real World Connection:

Whenever we are driving, we feel as if we are not moving at all because we are moving at a constant speed with the car.  Now when the car starts to slow down, our bodies continue moving forward at the same speed.  This is the reason we have seat belts.  If we did not have them, whenever the car slowed down or came to a stop, we would fall out of our seats.  This is a great example of Newton's First Law of Motion!

## Sunday, October 28, 2012

### Impulse Lab

Purpose:
The purpose of this lab was to discover the impulse, or change in momentum of an object.  We also discovered the relationship between impulse, force and time during a collision.

Procedure:
We used our red cart with an aluminum ring attached to it and ran it into the blue cart which also had an aluminum ring and therefore made a collision.  We used a force probe to determine the force of the collision and a range finder to determine the velocity before and after the collision.  Then the computer found the area of the "Force Time Graph." By finding the velocity and having the mass of the carts, we were able to find the momentum before and after the collision.  Because we found the momentum and the concept of impulse is described as "change in momentum," we found the impulse.

Data:

This is our graph that the computer gave us when we did the experiment

Velocity before= .627 m/s
Velocity after= -.5791m/s
Area= -.3579 N
Momentum before (m x v)= .15675 kgm/s
Momentum after (m x v)= -.144775 kgm/s

Now that we had enough information to find the impulse of the collision, we plugged in the numbers into the impulse equation which is:

J= pAfter - pBefore --> (impulse measures the change in      momentum)
OR
J=F x T --> (area of force - time graph)

Big Questions:

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

Summary of the Big Question:
Impulse is a change in momentum therefore because momentum is conserved, impulse is also conserved.  If you change the time in which the collision takes place, than the force will also change because impulse is always the same.  An example we saw in class was some bending your knees when you land a jump.  Because you expand the time in which the collision takes place, there will not be as much force in the collision and you will not hurt yourself.

Above is a link to a video that shows the infamous collision between Buster Posey and Scott Cousins.  Although it is one of the saddest things to watch and think about, it demonstrates impulse perfectly.  Because Cousins is running toward Buster as fast as he can and hits him with as much force as he thought it would take to score, the collision changed Buster's life (and the Giants' chances of making the playoffs).  Even though they experience the same force, Cousins, the body in motion, transfers his momentum to Buster, causing him to fly back in a twisted Motion that sadly ended the young catcher's season.

### Collision Lab

Purpose:
The Purpose of this lab was to understand the difference between elastic and inelastic collisions.  We also compared scalars and vectors; specifically the conservation of momentum versus that of kinetic energy.

Procedure and Data:
In this experiment, we put a red cart and a blue cart (both .25 kg), on opposite sides of the track.  To record the velocity before and after the collision, we put range finders on each end.  We performed two collisions, one elastic and one inelastic.  For the elastic collision, we pushed the red cart rightward towards the blue cart and as a result, they both moved to the right but the red cart had a much slower velocity.  For the inelastic collision, we again pushed the red cart rightward toward the blue cart, but this time they stuck together because of the Velcro.  This caused them both to move to the right.

Our data shows the momentum, kinetic energy and velocity of each collision before, after and combined.

Then we found the percent difference of each collision:

By finding the percent differences, we were able to conclude that momentum is better conserved than kinetic energy.  This means that less momentum is lost to other factors so it is a better way of measuring a collision.

The 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?"

Summary of the Big Questions:

1. In an elastic collision the cars bounce off of each other, so energy is lost to other factors.  In an inelastic collision the cars stick together so less energy is lost.
2. Momentum is better conserved than energy because energy can be lost to other factors such as heat, sound, friction etc. whereas momentum is dependent on mass and velocity so energy is only transferred between the two carts.

Connection to the Real World:
An example of an elastic collision that is bowling.  When a bowling ball is rolled down the lane towards the pins, there is not only enough force to knock them down, but in some cases, go flying into the back.  This is because the momentum in the ball transfers to the pins, causing the pins to fall down and if your good, get a strike!

## Sunday, September 30, 2012

### Rubber Band Cart Launcher Lab

Purpose:
The Purpose of this lab was to discover the relationship between velocity and energy and to determine what kinetic energy is and derive an equation for it.

Data:
In this experiment, we used a sensor to determine the velocity of the red cart.  We used a rubber band to launch it and did so at 5 different distances.  We did two trials for each distance and averaged the results to strengthen the accuracy of the cart's velocity.

Here are our group's results:

 Rubber Band Stretch (m) Velocity (m/s)(Trial 1) Velocity(m/s)(Trial 2) Average Velocity(m/s) Average VelocitySQUARED (m/s)2 Energy(J) **From last week's data! 0.01 .084 .074 .079 .00624 0.003 0.02 .166 .168 .167 .02789 0.013 0.03 .263 .278 .271 .07317 0.028 0.04 .364 .380 .372 .1384 0.050 0.05 .532 .533 .532 .28356 0.079

we then graphed our results:

Kinetic energy:
We used an "LOL" chart to understand Kinetic energy.  We learned from this chart that when we pull back the rubber band, we do work, which gives potential energy to the rubber band.  The potential energy becomes kinetic energy when the rubber band the rubber band is released and puts the cart into motion.

the equation for Kinetic Energy is
K=1/2m(v^2)

K= kinetic energy
m= mass
v^2= velocity squared
• This is a linear equation
• This is the equation for the energy of ANY moving object

The Big Question:

How are energy and velocity related?

Summary of the Big Question:
Through this experiment, I concluded that as the energy increases, the velocity also increases.  Therefore, if I give something a lot of energy, the object will move fast.

Connection to the Real World:
An example of the relationship between velocity and energy is the Extreme Skyflyer at Great America.  The farther the people are propelled back, the more energy is stored.  Therefore, the faster they will "fly" and the scarier it is.