Unit Summary # 3

In this unit we studies 6 major topics:
1. Newton's 3rd Law and Action-Reaction Pairs
2. Horse and Buggy/ Tug O' War
3. Nonparallel Forces
4. Gravity and Tides
5. Momentum and Impulse Relationship
6. Conservation of Momentum

Newton's 3rd Law
Newton's 3rd Law states that every action has an equal and opposite reaction. When talking about this law in action, we use the term action-reaction pairs. Below is an example.

In the picture above, earth PULLS the book DOWN, the book PULLS the earth UP.

Three things you should remember when writing a action-reaction pair:
1. The verb stays the same
2. The directions switch
3. The objects stay the same but trade places

Parallel Forces: Horse and Buggy Problem
Something that goes hand in hand with Newton's 3rd Law, action-reaction pairs are composed of parallel forces. One of the examples we stressed the most during this unit was the horse and buggy problem, which I will show and explain below.

The horse and buggy pull each other an equal and opposite amount. So, how does the horse pull the buggy? The horse has a greater force with the ground and by pushing the ground back, the horse moves forward, along with the cart.

Nonparallel Forces
Nonparallel forces sounds like a pretty broad topic when you say it, and thats because it is. Nonparallel forces occur a lot in life. For example, when you're hanging something with a rope, nonparallel forces in those ropes are keeping the object suspended. Or when you are boating, the current or wind will change your direction. Below I will show you an example and further explain it.

If you were to paddle your boat straight, your boat isnt't going to go straght because there is a nonparallel force of wind of  a current. This causes the boat to go diagonal, as seen above.

Gravity and Tides 

The Earth's natural tides can be explained through the pulls of gravity and Newton's 3rd Law.

Each day there are 4 tides in total:

>>2 high tides

>>2 low tides

Because the distances are different, point A and point B will experience different forces from the moon's pull. We know that Force and Distance are inversely proportional.

Therefore, 

>>Since B has a greater distance, the force will be lesser

>>And since A has a lesser distance, the force will be greater

This difference in force is what causes a tidal bulge.

The sun is also effects the tides, but not nearly as much as the moon. However, specific alignments of the sun moon and earth cause different tides, called Spring and Neap tides. 

When talking about tides you use the formula:

Which is the Universal Gravitational formula. Notice that distance is squared, unlike mass, that is why the moon has a greater effect than the sun on the earth's tides.

Momentum and Impulse Relationship

Momentum is defined by the letter p in physics, and it is equal to mass times velocity.

p=Mv

So, the momentum is directly proportional to the mass and velocity of an object. 

An impulse is what causes change in momentum, and is also defined by the numerical change in momentum, which can be found with formula 

J=p(fin)-p(int)

Impulse, or J is also defined by the formula

J=Force * Change in time 

The Conservation of Momentum 

Conservation of momentum states that momentum can be made or destroyed.

The two most important equations to remember when explaining conservation of momentum are for objects hitting and bouncing and objects and objects hitting and sticking.

When an object hits and bounces or explodes you use the following equation:

MaVa+MbVb=MaVa+MbVb

When objects stick you use the following equation:

 MaVa+MbVb=Ma+b(Vab)

Good thing that the floor is squishy!

Tides Resource

>> Why was this helpful?

      Even though I remembered a lot about tides from when I learned it in middle school, this video reminded me of things I had previously forgotten. It also had a lot of interesting fun facts that were interesting to know, even though I didnt need to know them. Plus the effects are cool. The earth will experience two high tides each day and two low tides per day. There will be approximately 6 hours between the different kinds of tides, 12 hours between tides of the same sort.

      The difference in force that is felt on opposite sides of the world can be explained by the difference in distance between the side of the planet and the moon. The side that is closer to the moon will experience a greater force. This difference in force causes the water to be pulled away from the surface of the earth, thus creating tidal bulges.

   
     Above you will see diagrams of  spring and neap tides. Spring tides will occur when we are experiencing a new moon or a full moon. Neap tides will occur when we experience a quarter moon.

     The chart above is a tide chart from Bald Head Island, NC. At the current time, they are experiencing a low tide. The are experiencing a neap tide, because it is a quarter moon. 

Newton's 3rd Law Resource

>> Why was this video helpful?

This video puts Newton's third law in a situation that I can understand. Real world examples help me better understand how the law is applied outside of the examples given in class. Plus, I just thought it was cool that a video like this was even made.

Unit Summary # 2

In this unit we learned 3 main topics:
1. Newton's Second Law
2. Air Resistance
3. Free Fall
     > Straight Down
     > Thrown Straight Up
     >Thrown Upward at an Angle
     > Projectile
   
>> Newton's Second Law
Newton's Second Law states that acceleration is directly proportional to force, and inversely proportional to mass. This can be defined in the following equation:

 a = F/m 

Another way this equation is shown is

F=ma

One thing that is key in Newton's Second Law is remembering that weight and mass are two different things, thus they are not interchangeable in an equation.

For example, if the given mass of an object is 10kg, you must find the weight. You do this by using the following equation: 

W=mg

Which means weight equals mass times the force of gravity, which is always 10m/s^2. So, if the given mass is 10kg, times the 10m/s^2 force of gravity, the weight of the given object is 100N (since weight is always written in Newtons).

>> Free Fall: Straight Down

Free fall is when an object is falling down with only the force of gravity acting upon it.
There is no air resistance in free fall. So, the only time free fall can happen is when it is in a vacuum.

In free fall, the object with accelerate at a rate of 10m/s^2.

In order to calculate the distance that the object has fallen you use the formula:

d= 1/2(g)(t)^2

Which means, distance equals one half gravity times time squared.

When calculating how fast the ball was going when it hits the ground, you will use the formula:

v= gt

>> Free Fall:Straight Up

The difference between normal free fall and being thrown straight up is that when something is thrown up, it has an initial velocity. 

Due to gravity, the object will decelerate at a rate of 10m/s^2 on its trip up, and will gain speed at the rate of gravity on its way down.

We are still able to use the equation for distance that I wrote for free fall. However, you do not use the total time that the ball is in the air, you use the time it took the ball to reach the top of its path. 

>>Free Fall: Projectile

Projectile motion falls at the same rate as something in free fall would, however, there is also a horizontal velocity. So, when dealing with projectile motion, one must take both velocities into account. 

Horizontal velocity will remain the same as the object travels. In order to find the horizontal distance you will use the equation: 

In order to find the time the object is in the air you will use the equation:

d= 1/2(g)(t)^2

which you can then plug into the horizontal distance equation.

Remember that when you are trying to find exact velocity, that you can make right triangles out of horizontal and vertical velocities. When both legs of the right triangle are equal, the hypotenuse is equal to that number time the square root of 2, which equals 1.41. 

>>Free Fall: Thrown Up at an Angle

This combines the skills that we learned in throwing straight up, and projectiles. You will use the same equation as before to find the distance from the ground at the highest point: 

                             d= 1/2(g)(t)^2

And you will use the same formula to find the horizontal distance the object will travel:

                                    d=vt

Also keep in mind what I said about exact velocities.

>> Air Resistance

There are two things that change air resistance:

>Speed

>Surface area

As the speed or surface area increases, the air resistance will increase, as well.

If a person were to jump off a building, their Fweight will be greater than their Fair (air resistance). In order to reach equilibrium, or terminal velocity, the person increase their speed to reach a point where air resistance will balance it out. 

Here is my group's video for this unit.

Newton's Second Law Resource

>>Why was this video helpful?

I found this video to be helpful because it further explains the physics of skydiving which is something I have trouble understanding. This explanation help me comprehend things I did not quite grasp beforehand. It summarizes what we learned in class.


 

Reflection

During this unit, I believe that I was a combination of both a procedural learner and a committed learner. I think this because I understood what I needed to do to receive a good grade in this course but I also committed what we learned to long term memory. I have to say that I didn't have much difficulty during this unit. All of the concepts were pretty clear and easy for me to grasp. I studied by redoing homework problems and going over any problems I struggled with multiple times until I fully understood it and knew that I could do the same with a similar problem. I did take advantage of the time that we had in class. Out of class I did my homework, and occasionally mention inertia when something reminded me of it. I predict that i did well on the unit test. I knew all of the formulas and i felt comfortable answering the questions and I felt confident in my answers. All your your feedback was pretty positive about all the work have I done. To me, this mean that I should continue working with the same diligence as I did during this unit. I got better at using the formulas we learned and how to properly adjust them in order to fit the problem. I would give myself a 4 effort grade for this unit. I feel like I put a lot of effort into this class. I participated in class and also did all of my work outside of class. I aimed to be productive, and I feel like I achieved at that. I am looking forward to the next unit.

Unit Summary # 1

During this unit of physics, we have learned a lot. We have learned the main concepts of all the following: Newton's first law (inertia), net force/equilibrium, velocity, acceleration, and graphing.

>> Newtons First Law:

Newton's first law states that an object at rest (or motion) will stay in motion (or rest) unless acted upon by an outside force. 

The picture above shows something that one could do to show inertia in action. When the person pulls the piece of paper, they are acting as an outside force. You may think that the coin will move with the paper, but silly you. Though there is  a force on the paper, there is not a force acting on the coin. So,when the paper moves, the coin will not change positions, thus, falling down into the cup. We have tested and learned about many other examples like this one, like pulling a table cloth from under your dishes, or leaving a cup on your trunk. They all have a similar explanation to the example shown above. 

>> Equilibrium and Net Force:

In this section, we learned what both net force and equilibrium are, as well as how to calculate the net force on an object. 

In the image above, the little blue box has a net force of 0N. Force is measured in Newtons (N) which is equivalent to about 1/4 of a pound. We can figure this out by subtracting the force from one side by the force on the parallel side. To find net force you must add or subtract parallel forces, otherwise it is not a correct net force. When an objects net force equals zero, the object has achieved a state of equilibrium. An object has reached an equilibrium either when it is at rest or in constant motion. If the force on one side of an object is greater than the parallel force, the net force will not equal zero. Also, if you were to try to push a box that was 5kg and a box that was 50kg, you would have to use greater force on the 50kg box. This is not because it is heavier, but because it has a larger mass, which means there are more atoms to make move in one direction. 

>>Speed and Velocity:

Speed is how far an object travels in a set amount of time. You may think that speed is the same thing as velocity. I did, but it isn't. The big difference is that velocity is direction specific, meaning that the velocity will change if the direction of the object changes. So, though you can drive at a constant speed, if you change direction, you will not be traveling at a constant velocity. Velocity changes also when an object accelerates, or accelerates in the opposite direction (slows down). 

To find an objects velocity, you must know distance the object has traveled, and how long it has traveled. The equation to find velocity is 

velocity=distance/time

You can also plug in the values and move around the equation to fit the specific problem.

>> Acceleration:

Acceleration is the rate at which an object's speed is increasing. Acceleration can be calculated by using the following equation

acceleration= change in velocity/time

The acceleration of an object can be increasing, decreasing, or constant. 

In example A, the acceleration will be constant. In B, the acceleration is increasing and in the final example, C the acceleration is decreasing.

When writing acceleration as units, it must be written as m/s^2.

Another important formula to know that applies to acceleration is 

distance=1/2(acceleration)time^2

This equation is used to calculate the distance that an object has traveled when the given acceleration is constant. 

>>Graphing:

We are able to use the acceleration data we collect as points on a graph by using time as our X coordinates and velocity as our Y coordinates. You can put these points into Excel, and go through the steps to calculate a line of best fit. The equation of a line is actually very similar to one of the equations that we use. 

Equation of a line: y=mx+b

Formula for distance with constant acceleration:d=1/2at^2

In this class, the b value is so close to zero that we do not use it. In the equations, m(slope) is 1/2a and x is interchangeable with t^2. By using the equation of the line, we are able to calculate the acceleration of an object. 

For a further explanation of what you need to know about graphing, here is a video that my group and I made:

YAY PHYSICS!!!

Hovercraft Lab

>> Riding a hovercraft feels different than any other thing I have ridden before. If anything, riding a sled is similar to the feeling, but you don't have to be on a slope in order to ride it. You move at a constant speed making it unlike ride a skateboard, car, bike, scooter, etc. If you have never ridden a hovercraft before, it is a little intimidating. The loud noise is somewhat off putting, but the ride is completely worth it. Make sure the people who are stopping you are reliable, because if they don't stop you, the next wall will.


>> The hovercraft was originally at rest, until an outside force (the two people pushing) made it move. Once it started moving, it had little resistance with the ground, allowing it to continue to move with little outside force slowing it down. While it was moving it was at an equilibrium, and while it was starting and stopping it had a net force because it had outside forces acting upon it. 

>> The acceleration depended on how hard the person was pushed.

>> Once the hovercraft reached an equilibrium, it had a constant velocity. 

>> Some members were harder to start and stop because they have a larger mass. A larger mass means that there is a larger number of total atoms that the outside force has to make move/stop. Thus, members of our class with a larger mass were harder to start and stop. 

Inertia Resource

>> Why was this video helpful?
     
I found this video to be helpful because it showed Newton's First Law in action. Newton's First Law states that an object in motion or rest will stay in motion or rest, respectively unless acted upon by an outside(unbalanced) force. The egg was the object that wanted to stay at rest, so even though the pie pan and toilet paper roll were moved, the egg just wanted to keep doing what it was doing, staying still. This video was a simple way of capturing inertia in action. 

Intro Post

What do I expect to learn in physics?

  

   >> I would like to learn how I will use physics in my future science courses and possibly how I will use it in my future career.

   >> In addition to the bullet point above, how does it relate to my past science courses?
>> What role does physics play in my daily life?

Why is physics important?

  

   >> I can apply what I learn in physics to many future classes I will take.
>> Physics plays a role in every second of daily life. That is why it is important to at least have a basic foundation in physics.
>> I will be able to explain things that relate to physics that I couldn’t previously explain.

What questions do I have about physics?

   >> What exactly is physics? I have a basic understanding of what the goal of learning physics, but have never understood what exactly the purpose behind the study as a whole is.
>> How has physics changed science as a whole?

What goals do I have for physics this year? 

>> Make good grades, as well as having high effort.

   >> Complete daily assignments and have them in on time.
>> Be well prepared throughout the year.