Unit 3

Unit 3 Summary Blog 

    

                         This unit was all about Sire Issac Newton's third law and momentum.   

Newton's 3rd law states that:  For every action, there is an equal and opposite reaction. 

Firstly we will start  with the concept of action and reaction pairs. 

Action Reaction Pairs are when a force is being applied to something and then that force is returned because Newton's Third Law tells us that for every action there is an equal and opposite reaction.

In this example we have a horse pulling a buggy, and the corresponding vectors. 

         The "pink" vectors show that the horse is pushing on the ground, and that the ground is pushing back on the horse with an equal and opposite force.  

        The grey vectors show that the buggy is pushing on the ground, and that the ground is pushing back with an equal and opposite force.   

        The "orange" vectors show that that the horse and the buggy are both pulling on each other with equal forces.                                    

   Ok, so why does the buggy move in the direction of the horse if they are pulling on each other with equal force?   This happens because the force that the horse is pushing on the ground with and the return force that the ground pushes the horse with, is greater than the forces between the buggy and the ground.  

  We can tell that the forces between the horse and the ground are greater than that of the forces of the buggy and the ground by measuring the vectors of each.  

          Have you ever stopped to consider what is happening between that book sitting on the table over there?   Whats that, you haven't? Well lucky for you I'm about to tell you.  lets look at this example. 

                                   

Here we see that the book is at rest on the table, and that the table itself is also at rest.   

In this example we have two action reaction pairs.    

                FIRST: the book is is pushing down on the table.  And the table is pushing back with an equal force on the book.  

           SECOND: the table is being pulled down by the earth, and the earth is being pulled up by the table. 

                Next up we will talk about tides and what causes them.

Tides are the movement of the oceans water over the face of the earth.    

Tides are caused by the Difference in forces  felt by the opposite sides of the earth.  

The moon is the most important factor in causing the tides.  Although it is much, much, much, smaller than the sun, we know that it has a greater gravitational force on the earth than the sun.  we know this because the Universal Gravitational  Equation:                              

. 

  What that shows is that distance is much more important than size when it comes to gravitational pull.  

 What we see here is the location of the moon during spring and neap tides.  
The spring tide occurs  when the moon, earth, and sun all line up together . and since the tides are caused by the difference in forces between opposite sides of the earth, this causes a greater force to be implied.   Thus the tides are the most extreme highs and lows that they will be.  

When the moon is at a 90 degree angle from the earth and the sun, we experience what are called neap tides. These are the least extreme highs and lows of the tides that occur. 



                   Next is the concept of momentum.  Momentum is represented by "P"  and the equation for momentum is  P=mv.     What this means is that momentum equals the mass of the object multiplied by the velocity.   
   Just like everything else, momentum has laws that is must follow.  One of these is that momentum is conserved.  What this looks like is that
                                                                         P-before = P-after

Finally we have impulse which is represented by "J" .    Impulse equals the change in momentum. And impulse equals force multiplied by the change in time  
                                                                                       J= F x t
And change in momentum looks like:  P= P-final  -  P-initial

We use impulse to tell how great the force of something  like an impact is .

                                                                            Tides

This is an extreme example of tides called a Bore tide.   This takes place in Alaska and is such a unique tide that it creates a visible wave that can even be rode into shore.  

                            

This is not by any means a normal tide.  But what are tides and why do we have them?
Tides are the movement of the oceans water in a rising and falling pattern.  The tides are caused n the difference of forces between opposite sides of the earth relative to the moon's gravitational pull.
The difference in the forces is caused by the distance from one side of the earth to the other. what this causes is tidal bulges that form on the sides closest and furthest from the moon, and leave the sides in the middle with the most average tide.  When the moon is either lined up directly with the sun or is directly opposite the sun relative to earth we get what is called spring tides.  when the moon is and a ninety degree angle to the earth and sun, we experience neap tides.


This is the tide chart for Panama City, Florida.

Right now, the beach is at a low tide

Panama City, St. Andrew Bay, Florida 30.1517° N, 85.6667° W 2014-11-17 6:09 AM CST Sunrise 2014-11-17 10:45 AM CST 0.57 feet Low Tide 2014-11-17 4:45 PM CST Sunset 2014-11-17 7:58 PM CST 0.94 feet High Tide 2014-11-18 5:48 AM CST 0.44 feet Low Tide 2014-11-18 6:10 AM CST Sunrise 2014-11-18 4:44 PM CST Sunset 2014-11-18 7:54 PM CST 1.08 feet High Tide 2014-11-19 5:59 AM CST 0.27 feet Low Tide 2014-11-19 6:11 AM CST Sunrise 2014-11-19 4:44 PM CST Sunset 2014-11-19 8:08 PM CST 1.21 feet High Tide 2014-11-20 6:12 AM CST Sunrise 2014-11-20 6:28 AM CST 0.10 feet Low Tide 2014-11-20 4:44 PM CST Sunset 2014-11-20 8:33 PM CST 1.35 feet High Tide 2014-11-21 6:13 AM CST Sunrise

Currently the Beach is experiencing Spring tides.

Moon: 16.0%

Waning Crescent

Current Time:Nov 18, 2014 at 8:27:44 AM

Moon Direction:↑ 148.63° SSE

Moon Altitude:72.51°

Moon Distance:246768 mi

Next New Moon:Nov 22, 20147:33 AM

Next Full Moon:Dec 6, 20147:27 AM

Next Moonset:Today3:08 PM

Unit 2

          During this second unit, we continued to discuss, learn about and base our work on the laws of Sir Issac Newton. The law that we learned about and worked on during this unit was Newton's second law.

Newtons second law states that:  Acceleration is directly proportional to force, and acceleration is inversely proportional to mass.   What this looks like as a formula is
                                                                        a = F x 1/m   or a = F/m
                                                                        a = acceleration   F = force  m = mass
           When we say that acceleration is directly proportional to force, what that means is that as an objects acceleration increases so to does the objects force.  And as the objects acceleration decreases so to does the objects force decrease.
                      acceleration (increase) = Force (increase)             acceleration (decrease) = Force (decrease)

           The other portion of the law says that acceleration is inversely proportional to mass.  What this means is that as the mass of an object increases the acceleration of the object will decrease.  And as the mass of the object decreases the acceleration of the object will increase.
       mass (increase) = acceleration (decrease)                       mass (decrease) = acceleration (increase)
       
         We tested this law with an experiment in class using a rolling cart, and hanging weight, and changing the locations of the mass of the system, and recorded the changes in the acceleration of the system.  Notice how I said that we changed the locations of the mass of the system?  This is important to note because throughout the experiment we were moving weights around to different locations on the system, but the net weight of the system remained the same throughout.

[      ]         = = =                 &
cart^      weights^      hanging weight^

             for the first run we had all of the weights on the cart and none on the hanging weight.  This resulted in a minimal acceleration because the mass of the cart was great, and Newton's third law tells us that mass and acceleration are inversely proportional.
run 1.)    [===]-------
                                 &      
           For the second run we placed one of the weights on the hanging weight.  What this caused was a greater acceleration than in the previous run.  This is because the the net weight of the system remained constant but the location of the weights caused the hanging weight to accelerate more than the time before resulting in a greater acceleration of the cart.
run 2.)    [==   ]------
                                =
                                &
   Runs 3 and 4 also saw that the cart's acceleration continued to become greater every time the weights were transferred to the hanging weight.
run.3.)    [  =   ]------
                              ==
                               &
run 4.)    [       ]------
                            ===
                              &


                Next is the concept of free fall.  In Free fall:
* the acceleration is 9.8m/s^2 in real life, or 10m/s^2 in the lab.  what this means is that the object that is experiencing free fall will accelerate 9.8m/s^2 faster that it was the second before.

             Similar to free fall, falling through the air also has an acceleration of  9.8m/s^2.   However in falling through the air the object is subjected to air resistance.  What this air resistance produces is something called a terminal velocity.

* Terminal Velocity is when an object is falling at the fastest speed possible and has an Fnet of 0 meaning that the force of gravity pulling the object down is equal to the force of air resistance against the object.  The amount of air resistance on an object depends on the mass, surface area, and speed of the object.  If any one of those variables changes, then the object's speed will have to adjust to the new terminal velocity.

            When throwing things at an angle, the only thing that determines the hang time of the object is the vertical distance. and to find this vertical distance we use the formula
                                                                                                          d=1/2g(t)^2

I really liked this video because it helped me understand Newton's Third law in the context of football.  I had actually been struggling with the concept in this setting and this video cleared many things up.


And FOOTBALL I mean, c'mon......

Unit Summary 1

Things I learned:
       One of the first topics that we addressed in this class was that of inertia and Newton's fist law.
Sir Isaac Newton's first law is that of inertia, and it states that: An object in motion will stay in motion, and an object at rest will stay at rest, unless acted upon by an outside force. This is Newton's first law and it explains the concept of inertia.
 
    This is a video that my group made explaining this concept of inertia.  We use multiple examples to show how inertia will keep an object moving unless that object is acted upon by an outside force, and how inertia will keep an object at rest unless it too is acted upon by an outside force.
Pay particular attention to the example with the cup of water, and the piece of paper being pulled out from underneath it.  Because in that example we are shown a property of inertia, and that property is that:
Inertia and mass are directly related, as mass increases, so does the inertia of an object.  And as mass decreases, the inertia of the object decreases.
                                                                                         mass ^=inertia^

   

       

  Another topic that we have spent time learning about this unit is Net Force and Equilibrium.
Net force is the overall sum of the force acting on an object.  lets see an example:

Say we have a box, and this box is being pushed with a force of 50 N to the right. (Hold on, before we go any further, let me explain to you what a "N" is and the other ways in which we measure force and mass. Mass is always measured in kilograms=kg.  While force is measured in Newtons=N.  It is important to understand the difference between the to units because you can not say that an object was being pushed with 10 kilograms of force, you could however say that the object was being pushed with 10 Newtons of force.)   Ok so back to net force and the example.
  The box is being pushed with a force of 50 N to the right.

                                                       50 N -----> [___]
But then something else begins to push on the box in the opposite direction to the left with 100 N of force.

                                                      50 N -----> [___]<-----100 N
At this point what is the Net Force on the the box?   lets do some simple math to find out.
Subtract 50 N from 100 N to find the answer is 50 N of net force. And the 50 N of net force are going to the left .                                                                       Net Force= 50 N



Now lets introduce the concept of equilibrium.  Lets take the same box, but this time it is just sitting still on a table.  And this time we know the box weighs 10 kg.
                                                                                10 kg
                                                       _________ [___] _______
                                                                    10 kg
Because the box weighs 10 kg, the table is pushing back against the box with 10 kg as well.  So using what we know about net fore, we can conclude that the net force acting on this box is 0 N.  When there is no net force acting on an object this is called Equilibrium.  Equilibrium is obtained whenever an object is experiencing zero net force, and can happen either while moving or at rest.
 
I got to experience what it is like to be at equilibrium while moving when we rode the hovercraft. the hover craft was drifting along with 0 net force and rode on a layer of air.  


       
                      Speed and velocity are two similar topics but vary from each other in very specific and important ways.   To find the speed of something we must know how much distance it is covering in some amount of time. to do this we use the equation: speed equals distance over time.
                                                                          speed = distance / time  
                                                                                      or                                      v=d/t
                                                                          velocity = distance / time

When we are measuring the speed or velocity of an object the most common measurement is                  meters per second.  =   m/s
                       
                                                                      SPEED VS. VELOCITY
     This is where speed and velocity begin to differ.  Velocity requires a specific direction to be maintained if you want to keep the velocity.  this direction is show using arrows called vectors.
                                                                  vector = ----->
Speed on the other hand does not allow for vectors.  This is because speed can remain constant while changing direction.  
              There are three ways to change the velocity of something.
                 1: by increasing speed
                 2: by decreasing speed
                 3: by changing direction
An important concept to understand is that you can have a constant (meaning unchanging) speed, without having a constant velocity.  But you can not have ha constant velocity without having a constant speed.

An example of this is a race track.   Lets say that he car is traveling at a constant speed of 200 m/s around the track. its speed is constant, but every time it makes a turn and changes direction, it also changes its velocity.



              Acceleration is a change in velocity over time.  This equation is written as
                                                                   
                                                                    acceleration = change in velocity over time
                                                                                   or
                                                                    a = change in v / t
 What acceleration really is, is the rate at which the speed of an object is increasing.  When we measure acceleration, we use  meters per second squared =  m/s^2.  
 One specific example of acceleration that is the same in all theoretical situations is the acceleration of an object due to the force of gravity.  Acceleration due to the force of gravity is 9.8 m/s^2.   What this means is that when an object is being pulled down to earth by gravity, the object is traveling at a constant increasing speed of 9.8 meters every second.    

            I have used the word constant to help talk about both velocity and speed. Now lets see what equations explaining these concepts actually look like and how we can use them to find out how far or how fast something is traveling while at constant velocity or acceleration.

                                constant velocity:                             vs.                      constant acceleration:
       How far? distance = velocity multiplied by time           How far? distance =  one half of acceleration
                                        or                                             multiplied by time squared.
                                      d=vt                                                                    d=1/2at^2
How fast? velocity = distance over time
                        v=d/t                                                        How fast? velocity = acceleration x time            
                                                                                                                v=at

This is the video Claire, Jillian, and I made to demonstrate Newtons first law of inertia.

Riding on a hovercraft feels like you are asleep in bed, but you can feel your body start to drift off. it is a smooth gliding feeling unlike any other.  I would tell you to be willing to let go of control and to just enjoy the feeling of no resistance (equilibrium).  It is different from any other form of transportation in that you do not feel the surface you are moving over.  I learned that when you are pushed on the hovercraft that once you are moving you have reached an equilibrium or constant velocity, and that the net force being implied on you are 0 Newtons.  Acceleration depends on the force applied in a direction, versus the force applied in the opposite direction. Constant velocity would be obtained when the hovercraft is no longer being pushed and is moving on its own.  Some members were harder to stop than others because they had greater mass, and therefore greater inertia.

Questions and No Answers (Physics Day 1)

     This year (2014), I, David Schill expect to learn everything! No really I do, because from what I have heard, physics is everything.  That means that I expect to learn why I cant hold a rope under my feet, pull up hard and quick, repeat this step over and over, and do some form of levitation. Secondly, I expect to learn why objects in free fall can only go as fast as their terminal velocity will allow them.  Thirdly, I expect to learn why certain metals conduct electricity better, or worse than other metals.
I think that studying physics is important because physics is what makes all the sports I love possible.  Physics explains why when your hands are you are cold you can rub them together and create heat.  And it is important to study physics so that automobile engineers  can better protect us from the forces involved in a crash.  This year my goals in physics include to maintain at least a B average, to test better than I have in previous science courses, and to come away with an applicable understanding of physics.   

Inertia

I Chose to use this video as an example of Newton's first law, because I feel it is a very relevant and serious real world example of inertia. The part of this video that really reviled new information and challenged the way that I saw and understood the role inertia in a car accident, begins at 50 seconds and explains what the purpose of head rest are.  The typical though on what causes whiplash in a car crash is that the neck violently snaps backwards.  While what is really happening is a gruesome example of Newton's first law which states that an object at rest will stay at rest, and an object in motion will stay in motion, unless acted upon by an outside force.   And what this video reviles to us is that the whiplash is not caused by the head moving away from the body, but instead is caused by the body moving away from the head.