Unit 3 Summary

1.) Newton's Third Law and Action Reaction Pairs:

 Newton's Third Law: Every action has an equal and opposite reaction.

For instance, a pair of tug of war teams are always pulling on each other with equal and opposite forces. A car and a truck crashing exert equal and opposite forces on each other. You state this pair like this:

Car pushes truck forward
Turck pushes car backward
(be sure to include vectors)

Or a skateboard:

- The effect that makes a difference in the pairs, especially one like the tug of war example, is friction. The greater force of friction allows one team or the other to win. Two things that affect friction are weight and the nature of the surface.

- Many times there are multiple action reaction pairs for every situation. For example, a grapefruit sitting on a table is pairing with both the earth and the table. These pairs are not equal and opposite necessarily, only the individual pairs are equal and opposite.
- Make sure to remember that accelerations in the opposite direction are negative.

This page contains great practice questions for understanding Newton's Third Law.

2.) Vectors 

Vectors are a device that show both direction and magnitude.  
More simply, vectors are arrows. We show magnitude with the length (and possibly opaqueness if you want) of the arrow, and the direction is the direction the arrow is pointing.

Adding vectors is helpful when determining the actual direction something will be traveling and the speed at which it will be traveling, by considering the forces acting upon the object.


A good example is a canoe on a river. If there is a current running south and you are paddling east, using vectors, you can determine where the canoe's path will take.

To add these vectors, draw lines parallel to each of the existing vectors, and then the line of actual direction is from the center to the intersection of the parallels.
Use this method also to help determine tension.

When trying to determine a lesser or greater tension, inverse the parallels so that they intersect the opposite line. The tension is represented by the distance between the center and the points of intersection. Be sure to put direction on the friction lines- I have made this mistake before. 

3.) Tides/Gravitational Force  
The formula for Gravitational Force is F=G m1m2/d^2

This formula explains the gravitational force between masses like planets. 
This equation and the information we can extract from it help explain a lot of things including tides.

Tides are caused by the gravitational force between the moon and the earth. Even though the sun has much (much much much) more mass, the closeness of the moon ultimately makes the force between the moon and earth greater and have a greater effect. 

The equation dictates that distance between the objects and the force are inversely proportionate. Same with mass, so the close distance between the moon and Earth made up for it's small mass.


-The Earth has a tidal bulge around it that is created by the moon's gravitational force and it creates high tides on each side of the moon and low tides on the adjacent sides.  The tides are caused by a difference in force from the moon because the distance is different at the two points relative to the center of the moon. There are six hours between each low and high tide and 12 between high tides and 12 between low tides. So, there are two low tides and two high tides each day. 

- When the moon and sun and earth are in line, the tides are called spring tides which are higher than the normal high, and lower than the normal low.When the sun is not in line it is rather during a quarter phase of orbit, it is called a neap tide. These tides are more lukewarm than the spring tides, in fact they are lower than the normal time tides. 

                                                           

This video is really helpful in understanding tides:

3.) Momentum and the Conservation of it

The momentum formula is p=mv
(the units for p is therefore kgm/s)

p total before= p total after (because of Newton's Third Law)



An important detail about momentum is that the momentum os a system is conserved. That is, 

When we are assessing two objects, like carts, collide, we can calculate the speed after by taking this assumption. Use this equation:

MaVa+MbVb= (Vab)(Ma+b)    - plug in the masses and velocities to find the velocity after the carts collide.

 
3b.) Impulse
Impulse (or J) is the change in momentum.

To change momentum, you need a change in force.
When thinking about changing the Force, two main things matter: 

1. The amount of Force applied  2. Time F is applied

For these things, we explain the equation for Impulse: J=F(change in t)

This equation shows that distance and force react in a certain way to each other. When time increases force decreases and vise versa. 

An Example of this would be landing on a hardwood floor rather than a memory foam mattress. The mattress increases the time of force applied (do not forget that the change in momentum/impulse is the same), which decreases the force. That is why you wouldn't get as hurt on the mattress. 
When answering these problems be sure to mention:

-That the object will go from moving to not moving no matter what
- The relationship between change in momentum and impulse
- The relationship between time and force when talking about impulse

This page helps to connect Newton's Second Law, Newton's Third Law and Change in Momentum in contribution to Impulse. The building blocks are really good to understand so check it out.

Tides

This Video explains tides well: It especially is helpful with the parts about forces on the earth with vectors and explanation. It also has a really cool demonstration of the tides in the program he has. The forces are the most confusing in terms of where the force is in relation to the core and the water on the surface and this video helps with that.



Because the moon is closer to the sun it is the force causing the tides not the sun even thought the sun has more mass and is pulling harder on the earth. The Earth has a tidal bulge around it that is created by the moon and it creates high tides on each side of the moon and low tides on the adjacent sides.  The tides are caused by a difference in force from the moon because the distance is different at the two points relative to the center of the moon. There are six hours between each low and high tide ad 12 between high tides and 12 between low tides.So, there are two low tides and two high tides each day.
There are different kinds of tides according to where the sun is relative to the moon and earth. If the sun is in line with the moon and earth it is called spring tides and it makes the high tides higher and the low tides lower. If the sun is not in line it israther during a quarter phase of orbit, it is called a neap tide.
http://www.tides4fishing.com/us/north-carolina/nags-head

http://www.tides4fishing.com/us/north-carolina/nags-head

Right now the tides are low, but they will be high very soon. 
It is in between but soon it will be neap tides.

Newton's Third Law Resource

The Physics Classroom link on Newton's Third Law:

This source was really helpful in strengthening my understanding of Newton's Third Law. It provides a very conclusive summary of the Law and it's meaning. It would be especially helpful in making the general idea and the abstract of the concept more concrete.

The site also includes examples and sample problems that you can try out and check your answer. I find these really helpful because often I read the text and think I retain the info, but the questions could reveal I don't.

This page on action and reaction pairs is helpful in understanding examples of the law and what they mean for actual objects. It also includes practice questions.

Unit 2 Summary

Unit 2 Summary:

The second unit was about Newton's Second Law:

Newton's Second Law is:
 acceleration is directly proportional to force and inversely proportional to mass.
or:
a=F(1/m)

In the Newton's Second Law lab, we set out to prove this. 
We did so by changing mass and Force to see how it would affect acceleration.

In the first experiment:
-we added mass and found that when we added mass and measured the acceleration, the acceleration decreased. 
-Then we graphed the data and compared the equation of the line to Newton's Second Law. 

y=mx+b
a=F(1/m)

The slope of the line is always the factor we kept constant during the experiment. 
in this case, it was force(we kept force constant by keeping the weight of the hanger constant).

When we compared the slope(theoretical force), to the actual force we measured(the wight of the hanger), we found that they were often within 10 percent of each other, depending on which group you asked. If it was within 10 percent, we can say that it suggests Newton's Second Law is true.

In the second expierement, we repeated the same procedure, but kept mass constant and increased force. We did so by transferring the mass from the cart to the hanger. We found that when we increaced the force, the acceleration also increased.

Then we learned about Free Fall, that is moving without air resistance. 

In free fall, the only force acting on the object is gravity. The force of gravity in free fall is 10m/s^2. 
-When a ball falls, the speed increases by 10 m/s every second. 

-When a ball is thrown up, it decreases every second by 10m/s. 
-at the top of it's path, the acceleration is 0 and it is at equilibrium. 
-When it falls back down, It increases every second again. 
*when calculation for a ball that has been thrown up and has come back down, you can only use the formulas if you measure the path it took starting at 0m/s.

For instance, to find the total time in the air, you must use d=1/2at^2 only for the path from equilibrium(at the top) to the ground. Then you can double the time to get the answer. 

Throwing things up at an angle:

When you throw things up at an angle, you must use the vector as the hypotenuse of a triangle with the other sides being vertical velocity and horizontal velocity. You treat the vertical velocity the same as you would throwing straight up as it increases by 10m/s when falling and decreases by 10m/s when rising each second. The hypotenuse of the triangle is used to determine the actual velocity at each second. 
*the angle may help you determine of the triangle is a special triangle

Projectile Motion:

When measuring projectile motion, you must take into account the vertical and horizontal properties. You must use different equations for each one: 

vertical:
d=1/2at^2
v=at

horizontal:
v=d/t
d=vt

Use each of these to find whatever part of the problem you are asked for, but make sure you are using the right equation. Hight determines time so the time will be the same for both of them.
To find the actual velocity at any given second, you create a triangle with the speed on each side, both horizontal and vertical, and the hypotenuse represents the actual velocity.

Falling Through the Air(Falling with Air resistance):
When falling through the air, you can measure the net force of the object with this equation:

Fnet=Fweight- Fair. 
Two things can affect the force of air resistance
-speed
-surface area

When you first jump off, your speed begins to increase, this increases the force of air resistance and you acceleration starts to decrease, as does your Fnet(see equation with increasing Fair). This does not mean velocity starts to decrease as well, in fact it continues increasing. When the object reaches terminal velocity, it is at equilibrium.

But, if the object were say a person skydiving, and that person reached equilibrium and then opened the parachute, the acceleration and Force would both decrease because the Fair increases because the surface area increased. Then the skydiver will reach a second terminal velocity, however, it is going at a slower speed than the first.
*The force of air resistance is the same for both terminal velocities.

Resource

http://www.physicsclassroom.com/mmedia/newtlaws/sd.cfm

This source helps explain the Physics of Skydiving.
This video is also helpful for understanding projectile motion:

https://www.khanacademy.org/science/physics/one-dimensional-motion/old-projectile-motion/v/projectile-motion-part-1

Unit 1 Reflection

Unit 1 Reflection

1.) This unit I was a combination of Procedural learner and Committed learner. I was procedural because i had to learn a lot of concepts really fast and I didn't focus a lot on the why or how for those concepts. But for the last part, the equations part, I asked a lot of questions and made sure I understood more than I needed to.

2.)I had a lot of difficulty grasping the Speed vs. Velocity concept. It makes sense to me on paper that velocity includes direction, but conceptually it was hard for me to understand what effect direction has. I overcame the challenge by asking questions.

3.)The way I studied throughout this unit was by making sure I understood how to do the questions of the homework, and for questions I missed on the quiz, I tried to figure out why(ie. I didn't study that, or I didn't understand etc.). I think in the future, I should continue to use that strategy. Also in the future I should start the blog post earlier as review.

4.)I took the opportunity in class to really focus on how to do the homework problems and other problems when we went over them in class which was helpful. Out of class I watched the videos on the website which explained a lot of concepts.

5.)I predict I got a high B. I think I was mostly able to demonstrate my understanding of the concepts, however, there were a few concepts I think I understood and had trouble applying. For future tests I want to make sure that I pay attention to the problems we do in class because they will help me learn how to apply the concepts.

6.) I learned from your feedback mostly in class when I thought a concept was one way it helped when you explained why it isn't that way. The feedback I hope for in the next unit is the same kind of explanatory help.

7.) I got better at working with other people and at  doing work when there isn't a definite headline, I just need to know the material. Hopefully next unit I will get better at something else, but I do not know what it is. Usually when I improve I don't know I need to until it presents itself as a problem.

8.) I would give myself A 8/10 for effort because if I were to have put as much as I should have retrospectively I should have come in and asked for sample problems on the first couple of concepts I missed because It would have helped on the test.

9.) you should know that I think physics is more interesting than chemistry so far.

What Did We Learn in Unit 1

What Did We Learn in Unit 1? 

Physics starts with forces and how they act on things.

The first concept adresses Newton's first law which is 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. Inertia describes an objects tendency to resist a change in rest or motion. Mass is a measure of Inertia. it may seem as though Inertia can be a measure of Mass because we are familiar with Mass first, however, it is the other way around.  An example of Inertia is suppose you have a refrigerator and a soccer ball. You try to move them both 10 meters, but it is very hard to move the refrigerator, and easy to move the soccer ball. The Inertia of the refrigerator is greater because it has more resistance to change it's state at rest.

Net Force and Equilibrium:

A force is either a push or a pull that acts on an object. The force is measured in Newtons(N). The Net Force is the sum of all of the forces acting on an object. If an object is at equilibrium, that means the Net force is zero. An object can be at equilibrium when it is at constant velocity or at rest. 

Example Question:

If I push on a box from one side with a force of 100N, and Caroline pushes on the other side with a force of 75N, what is the Net Force? Is the box at equilibrium?

Answer: 25N, no

Velocity and Speed:

Speed is a measurement of how fast an object is going. You measure speed by covering and objects distance in a period of time. An easily understood example of this is how we measure the speed of out cars- in Miles per Hour. As in, how many miles(distance) is the car covering in a period of time (miles).

Velocity is more specific because it refers not only to the distance in time, but also to the direction. An object can maintain speed, but change velocity by changing it's direction. This is because it takes an acting force to change direction. An example to think about is riding a bike around a baseball field. If you follow the perimeter, you can keep the same speed, but since your direction is constantly changing, your velocity is not constant.

There are two ways to change velocity: speed up/slow down, or change direction

The direction portion of velocity is shown using vectors, which are basically arrows. They convey both the magnitude, or the speed of the velocity and the direction.


Acceleration:

Acceleration is a change in velocity over a period of time. Speeding up is acceleration, but slowing down is also acceleration but in the opposite direction. Acceleration is measured in meters per second squared rather than just meters per second. If an object is falling straight down, the acceleration is always 10m/s squared.

Constant Acceleration and Velocity: Constant Velocity is when for any given time the speed and direction are the same. Constant Acceleration is when an object is speeding up or slowing down the same amount each second. Constant Velocity and Constant Acceleration are mutually exclusive. 

 Calculations:

https://www.youtube.com/watch?v=O2yG-5yiuhQ&feature=youtu.be


To calculate Acceleration you will need three formulas:

The equation for acceleration: acceleration = change in V/time

Distance:      d=1/2 a t^2
Speed(how fast):  v=at

Formulas for Velocity:

v = d/t
d = vt

Learn Them!