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 .
