Unite 3 Relfection

In this unit we started out by learning Newtons 3rd law: 

For every action there is an equal and opposite reaction. 

This is exactly as it sounds if I push you, you push me back with the same force I pushed you. For example imagine you hit a piece of paper, It doesn't feel like you hit it very hard does it. THat because the paper hits you can only hit the paper as hard as it hits back and the piece of paper doesn't hit you very hard. Now if you hit a punching bag, it would hurt because it hits you much harder than the piece of paper. 

In this unit we covered the following topics that pertained to Newtons 3rd law: 

Action reaction pairs 

How a horse pulls a carriage  

adding forces/vectors at angles 

Gravity and tides 

Momentum and Impulse/ Conservation of Momentum 

First lets take a look at action reaction pairs  

You see this book, it's just a normal book no tricks, but it is doing something very interesting, it's pulling the world up. Pretty amazing, as a matter of fact anything with has mass pulls at other things with mass. But how come we don't notice this book puling on the earth. 

As Newton said every action has an equal and opposite force.  This means that the book is being pulled by the earth the same amount of force that the book is pulling the earth. Now since the book has such a minuscule mass it doesn't really move the massive earth enough to be noticeable.  

Now say we put that book on a table

Now we have two forces acting on the book. the book pulls on both the earth and the table, but thankfully the table is strong enough that when it pulls on the book with an equal and opposite force it counteracts the earths pull and prevents the book from falling to the earth. 

Now that we know how action reaction pairs work we can ask the question: 

How does a horse pull a carriage? 

First off because of N's 3rd law we know that the horse exerts an equal and opposite force on the carriage and the carriage would do the same. So how does the carriage move? We also know that the Carriage has an equal and opposite force with the earth and that the horse has it's own equal and opposite forces with the earth.  

But, because the horse has hooves it is able to push on the ground much harder than the carriage allowing the horse to pull the carriage with some help form the earth.  

Adding forces/vector and angles: 

Lets imagine that the below picture is of a person being pushed north stream by a stung stream and he wants to get across to the left side. The stream is the green and the persons current trajectory is the red going right.

 North

South                             Southeast

If the person followed the red line he would end up down southeast of the shore (Quadrant 2 in the graph). But lets say the guy positioned himself the way the white arrow is and started rowing, he would end up right along the red lines path, just where he wants to go. 

Lets also imagine that the top of the green line has a force of 100 N's and the right side of the red line also has 100 N's. If we also imagine the two different lines represent the vectors of two guys pushing a couch then the couch would be pushed in the direction of the white line. and if we remember back to Unit two and adding vectors we would know that the couch is being pushed with a force of 141 N's.  

Gravity and Tides:

In this unit we learned that something with mass attracts all other things with mass and that Force depends on the mass of objects and the distance between objects.

Inverse proportional law: the farther you get from something the more squared it is ( the less force you it has on you). That means that person standing on top of a mountain would have less force pulling on him compared to someone standing at sea level

In order to find your force at any given time we use the Universal Gravitational Formula:

F= G m1m2/d2

We know that the moon exerts a force on the earth because it has mass. Because there is so much water on earth it is going to be pulled toward the moon, but it doesn't just get puled to one side of the earth. Lets say the moon is on side A and the force of earth on moon is 25 N. Next lets say

 that the opposite side of A is B and B pulls on the moon with a force of 5 N. The center of the earth is also pulling on the moon with a force of 15 N. If we were to subtract 25 and 15 we would get 10 and if we were to subtract 15 with 5 we would get -10. It's because of these two equal and opposite forces that we have tides on both sides of the earth.

The above diagram shows the spring and neap tides. A spring tide is where the moon and the sun
 are aligned with the earth making higher tides than normal. A neap tide is when the moon is not aligned with the earth and is generally a half moon.because it's not aligned witht e earht it doesn't give off as much force making the tides smaller.


Momentum and Impulse/Conservation of momentum.


Momentum is defined as P=MV
Impulse as J=F change in T

If we want to find the momentum of soemthing we just do the equation

Change in P= Pfinal- Pinitial

to find impulse

J= F change in T


 When things stick together

ptotal=ptotal after

or

MaVa+MbVb=Ma+b(Vab)


 When two objects hit there momentum will be conserved.

This is true because

Fa=-Fb
then
F change in Ta= -F change in Tb
 which equals
Ja= -Jb
 equals
change in Pa = - change in Pb

if we take Pb and move it to the other side we would get

Change in Pa + change in Pb= 0

so therefore mass is conserved.

An example of this in action would be two people throwing eggs at each other and the egg doesn't break. Why doesn't the egg break?

We know that no matter how the egg is stopped it is going from moving to not moving and therefor the change in momentum is the same regardless of how the egg is stopped.

P=MV
Change in P = Pfinal- Pinitial

Since the change in momentum is the same regardless of how the egg is stopped, the impulse is also the same regardless of how quickly it is stopped.

Change in P = J


The egg tosser stop the egg over a long period of time, since the impulse is constant the force on the egg is small. A small force on the egg means it will not break.

 

 

 

Difficulties

I found this section very hard mostly because of the amount of math in it. But I know that I can over come this by practicing, because that is exactly what I did in my math class and my scores are already improving. I already feel more confident in taking the test because of this blog reflection, I thin it really helps for me to right down everything I know in one place. My studding skills will definitely improve after this because I'll start to practice the equations more.

I hope to do better next unit by taking what I learn in class and in homework and working it over until I reach a deeper understanding of it.

Connections 

I think it's strange how everything pulls just a little bit on everything else with mass. Now I understand how scientist believe black holes are made, If everything pulls on each other and some little mass is taken away then I guess that creates an imbalance in the forces causing a massive vacuum.