Unit Six: Unbalanced Forces part 2

To depict the forces acting upon an object you would draw out a free body diagram. A free body diagram is a diagram showing all the forces exerted on an object with all its surroundings removed. The diagram consists mostly of a sketch of the object stated and arrows representing the forces exerted upon it. For example:

Here is a yoyo hanging from a string. It is at rest.

Here is the free body diagram of the forces:

The bottom picture is how you would depict forces that are balanced; here is an example of unbalanced:

·            A basketball is moving to the left with friction.

·            The normal force and the weight are balanced but there is no opposite force to balance out the friction.

·            So this is unbalanced.

We also learned how to calculate the acceleration of two objects on a pulley. Here is an example:

The blue box has the same tension and mass as the green box, the normal force and weight of the blue box are balanced but there is negative tension on the blue box as it moves towards the pulley. The green box's positive tension pulling up and the weight are balanced. The mass of the boxes are 12 kg. Now this is how you find the net force and the acceleration of the situation.

 

Let's start with acceleration, you know the mass and the Earth's gravitational pull (10 m/s² ). So now using the equation mBg + t2 - t1 = (mB + mA)a. mBg is the green box's weight, mB is the green box's mass, mA is the blue box's mass, t2 is the green box's tension, t1 is the blue box's tension, and "a" is the system's acceleration. So plugging in the variables, you'll get:

 

12kg(10 m/s²) + t2 - t1 = (12kg +12kg)a

 

Since the tensions are equal they cancel each other out and then you get:

 

120N = (24kg)a

Now to find the acceleration, you divide the mBg over the sum of mB + mA:

120N/24kg = a

a = 5 m/s²

And now, to find the system's net force you'll use the mass (12kg, because both objects are of same mass) and the acceleration you found above (5 m/s²) as your variables with the equation:

Fnet = ma

Fnet = (12 kg)(5 m/s²)

Fnet = 60 N

So that is how you find acceleration and the force net of a system.

Unit Six: Newton's Laws and Unbalanced Forces

So basically, we didn't learn anything new in class but were instructed to do this blog so here it goes…

Unit 6, its about unbalanced forces and Newton's Laws. The opposite of unbalanced forces are balanced forces and balanced forces are, for example:

When a cellphone is placed on a table, and two forces are acting upon said cellphone. One is Earth's gravitational pull and it exerts a downward force. The other is the normal force or the component perpendicular to the surface of the contact, which in this case is the surface of the table, which exerts contact force between the cellphone and the table. The normal pushes upward on the cellphone. These forces are of equal magnitude and are moving in opposite directions, so the forces on the cellphone are balanced.

Now unbalanced forces are, for example:

When the cellphone is given a little push and set into motion from a rest. There are three forces acting upon the moving cellphone. One is Earth's gravitational pull, exerting a downward force on the phone.  The second is the normal force and it exerts an upward pull. The last force is friction, a force that opposes motion or potential motion on an object,  and it is directed opposite the cellphone's motion and will eventually cause the phone to slow down. The gravitational pull and the normal force are of equal magnitude and balance each other out but because there is no force that is of equal magnitude and of opposite direction there is nothing to balance the frictional force. What it comes down to is that the cellphone is not at equilibrium and then accelerates because unbalanced forces cause acceleration.

Here is an example of unbalanced forces, here I have a gift one of my friends got me (yes itʻs a ball, but itʻs the thought that counts), the ball was acted upon by a force that caused it to become unbalanced which led to its slow acceleration.... Well you get it... I hope :P


All of the information I found is from http://www.physicsclassroom.com/class/newtlaws/u2l1d.cfm

Unit Five: Newton's Laws and Equilibrium

In physics, we went over Newton's Law. Last night's post was also about Newton's Laws but were from the Internet. Today, Mr. Blake gave out the terms we needed to know for class for each law.

1.     Newton's First Law

a.     The Law of Inertia

b.     Objects at rest will stay at rest and objects in motion will tend to stay in motion unless acted upon outside unbalanced forces.

2.     Newton's Second Law

a.     The acceleration of an object is directly proportional to the net force on an object and acceleration is inversely proportionate to the object's mass.

                                               i.     a ∝ Fnet

                                              ii.   a ∝ 1/m

                                            iii.     a = Fnet/m

                                            iv.     Fnet = ma

b.     These equations mean that i) the acceleration of an object is directly proportionate to the force net of the same object, ii) the acceleration of an object is inversely proportionate to the mass of the same object, iii) the acceleration of an object equals the force net over the mass of the same object, iv) the force net on an object equals the mass times the acceleration of the same object.

3.     Newton's Third Law

a.     Action – Reaction

b.     For every action/force, there is an equal and opposite force/direction.

Here are some other things that you should know:

1.     Force – a push or pull

2.     Frictional  forces – forces that opposes motion or impending motion

3.     Contact forces – a force that acts at the point of contact of two objects

4.     Distance force – a force at a distance

5.     Balanced forces – uniform motions, or equilibrium that have no acceleration

Me being totally lame and trying to push my huge sofa to represent push and friction

Me being even more lame and trying to pull my other sofa to represent tension.

Unit Five: Newton's Three Laws

Newton's Laws:

Law number one, an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an external force (physicsclassroom.com). It is basically saying that if you are not moving then you don't leave the spot you are situated at. And if you are moving at the same speed and going in the same direction then you stay in a constant motion. So basically it's like standing at the crosswalk, waiting for the pedestrian light to say go. You stay at the curb waiting for the light so you are technically at rest. When the light says go you are moving at a constant speed till you reach the other side which is in the same direction with no change, so you are now in motion.

 

Here is a animation of rest and motion.

Law number two, the acceleration of an object is dependent upon two variables,  the net force acting upon the object and the mass of the object (physicsclassroom.com). Basically the acceleration of an object depends on: the net force which is the overall force or the sum of all forces acting on the object which is directly dependent, and the mass of the object which is inversely dependent. The overall force is like a basketball game, a successful play is dependent on your teammates, the other team and their plays. These together are like the overall force on an object. For mass, I think you guys get that, though mass is not weight it is still a measurement of something. 

Here is a really junk computer drawing of a play that I sort of remember doing when I went to KMS (Kaimuki Middle School), it represents overall force.

Law number three; for every action, there is an equal and opposite attraction (physicsclassroom.com). In translation, this means that forces come in pairs, that the size of the forces on the first object is the same size of the force for the second object, and that the direction of the force on the first object is the opposite direction of the second object. Like how everything comes in pairs, table items come in pairs like salt and pepper, sugar and cream, and ketchup and mustard. The opposite tastes are what make the taste buds neutralize... IDK....

Here is a animation of pairs, remember Mr. Salt and Mr. Pepper? Lol, well, yeah. :D

 

Just an animation I made...nbd...

Unit Four: Diagonals

Diagonals, in physics diagonals are a pain in the butt hole, especially when you try to calculate an object with a diagonal velocity. This is just a fast, to the point post on how to calculate a diagonal velocity's distance or time.

So this is how you start finding the values for your t-chart. You still need to use a t-chart because; a diagonal velocity is basically the vertical over the horizontal velocity. Anyway this is how you find the vertical and horizontal velocities:

1.     Know your givens: in these types of problems you are given the velocity of the diagonal and the angle of the diagonal.

2.     Remember and use SOH CAH TOA:

a.     SOH = sine = opposite/hypotenuse

b.     CAH = cosine = adjacent/hypotenuse

c.      TOA = tangent = opposite/adjacent

d.     The reason for why we need to know SOH CAH TOA is because, the diagonal velocity is like the hypotenuse of a right triangle and the horizontal and vertical velocities are like the adjacent and opposite sides of the triangle from the given angle.

3.     When finding:

a.     Vertical velocity, using the variables given which is the diagonal velocity and the angle, draw out the diagonal direction and triangle shape with the angle of the diagonal. Then, identify which is the opposite and which is the adjacent side of the angle. The opposite side equals the vertical velocity so using SOH CAH TOA you find the vertical velocity with the equation V_oy = (diagonal velocity) sinθ. (θ = the angle given)

b.     Horizontal velocity, it is the same as finding vertical velocity except instead of using sine you will replace it with cosine so the equation will look like this: V_ox = (diagonal velocity) cosθ.

So after you find the vertical and horizontal velocities, the diagonal velocity no longer exists and you use the vertical and horizontal velocities to find the other variables are in your t-chart. You already know the two initial velocities, the accelerations (vertical velocity = -9.8 m/s² acceleration and horizontal velocity = 0 m/s² acceleration), and the final velocity for the horizontal velocity, which is the same as the initial horizontal velocity. So all that is left to find are the distances, times and the final vertical velocity. You find these variables using the kinematic equations. Here is an example:

1.     Given variables: 150 m/s diagonal at 37°.

2.     Find the horizontal and vertical velocity:

a.     V_ox = cosine = (150 m/s)cos37° ≈ 119.8 m/s

b.     V_oy = sine = (150 m/s)sin37° ≈ 119.8 m/s

3.     Make a t-chart with what you already know:

a.     The initial vertical and horizontal velocities

b.     The accelerations for both the x-axis (0 m/s²) and the y-axis (-9.8 m/s²)

c.      The final vertical and horizontal velocities, because the x-axis has an acceleration of 0 m/s² so the final velocity is the same as the initial (119.8 m/s) and for the vertical velocities since it is a vector and is defined by magnitude and direction and since the direction is going downward the final velocity is the negative of the initial which is -119.8 m/s.

4.     Find the missing variables: both distances and the times:

a.     For the times, use the equation V_f = V_o + at.

                                               i.     -119.8 m/s = 119.8 m/s + (-9.8 m/s²)t

                                              ii.     -239.6 m/s =(-9.8 m/s²)t

                                            iii.     t = 24.449s ≈ 24.45s

                                            iv.     because time is a constant both the x and y-axis times are equal

b.     Find the vertical distance, use the equation dy = ½ ay(ty)² + Voy(ty)

                                               i.     dy = ½ (-9.8 m/s²)(24.45s)² + 119.8 m/s(24.45s)

                                              ii.     dy = -2929.23225m + 2929.11

                                            iii.     dy = -0.12225m

c.      Find the horizontal distance, use the equation dx = ½ ax(tx)² + Vox(tx)

                                               i.     dx = ½ (0m/s²)(24.45s)² + 119.8 m/s(24.45s)

                                              ii.     dx = 0 + 119.8 m/s(24.45s)

                                            iii.     dx = 2929.11 m

So that is how you find the variables.

Here is the Disney version of Robin Hood and here he is shooting an arrow at 150 m/s at 37 °.

Unit Four: The T-Chart and Projectiles

So far in unit four we learned about t-charts and how to calculate the speed, time and distance of a projectile. We are still using the same variables from the last two units, which are:

d = distance (meters)

a = acceleration (gravity of Earth = 9.8 m/s² or 10 m/s²)

t = time (seconds)

V_f = final velocity (m/s)

V_o = initial velocity (m/s)

And we are still using the kinematic equations we used in the last two units as well, they are:

d = (average V)t

d = ½ at² + V_ot

V_f = V_o + at

V_f² = V_o² + 2ad

T-charts list x-axis variables and y-axis variables, the variables are determined by the direction the object is going, anything going in a horizontal velocity/direction is a x-axis variable and anything going up or down velocity/direction is a y-axis variable. For example, a marble is pushed across a table at a velocity of 5 m/s and the height of the table is 2 meters. The velocity of the marble being pushed across the table is an x-axis variable, because its movement is horizontal (unless it's one of those funky Inspiration tables that are just there for ornamental value). The height of the table is a y-axis variable because the height of the table is the distance traveled when the marble falls off the table and the direction of the marble is then going downward.

Another way to know if something is an x or y-axis variable is by drawing out the direction of each variable. So, again, using the example of the marble this is what a drawing would look like….

The small graph that has a + in QI and a – in QII shows you what axis each variable is. So by going left or right makes a variable part of the x-axis, by going up or down makes a variable part of the y-axis. The + means that if the object is going up or moving to the right then it's velocity is positive, and the – means that if the object is going down or moving to the left then its velocity is negative. I guess this makes more sense than my big paragraph but I really don't want to delete it.

Anyway when trying to calculate the motion of a projectile you write down the given variables in a t-chart and then use the kinematic equations to find the other variables. Using the situation from before, you already know

·            the velocity of marble moving across the table (5 m/s)

·            the acceleration of the marble moving across the table (0 m/s²), because the final and initial velocity doesn't change because the marble is moving horizontally

·            the distance the marble will drop to the ground (-2 m), because it is falling downward the distance is negative

·            the initial velocity when the marble falls off the table (0 m/s), because the marble is now free falling it has no initial velocity

·            the acceleration of the marble during free fall (-9.8 m/s²), because, assuming that this place is on earth and earth's gravity pulls objects downward the acceleration is negative and equals -9.8 m/s²

With this in hand you can now fill out the t-chart, it should look like this:

Also, one exception to the values of the different sets of variables is that time is a constant and that both the x and y-axis share it.

To find the rest of the variables you must use the kinematic equations, here is how I found each variable….

Find the final velocity after the marble hits the ground.

Finding the time it took the marble to fall to the ground.

Finding the horizontal range as the marble falls to the ground.

Units 1, 2, and 3

With the "first quarter" finished, here is a summary of what we learned so far in physics. So far in physics, we've covered units 1, 2, and 3. In the first unit was mostly an introduction to physics; the second and third unit went into the study of movement.

The first unit was about getting us to be able to:

·            Know the difference between accuracy and precision

·            Know the IS standard dimensions and units of measurements

·            Be able to do simple dimensional analysis

·            Know how to use scientific notation

·            Graph the relationship between independent & dependent variables

·            Understand and be able to use different types of graphing methods.

This is a video/animation I made on accuracy and precision

The second unit was about getting us to be able to:

·            Describe & interpret motion through words

·            Describe & interpret motion using motion maps, diagrams & graphs

·            Differentiate between vector & scalar quantities

·            Determine the relationship between position & time of a moving object

·            Use the displacement, velocity, and instantaneous position formulas

·            Relate the graphical, algebraic and motion diagrams to one another

·            Use the appropriate units in a given problem

Here is a video/animation of how displacement works

The third unit continued from where the second unit left off, which was getting us to understand and be able to:

·            Contrast graphs of objects undergoing constant velocity and constant acceleration

·            Define instantaneous velocity

·            Distinguish between instantaneous velocity and average velocity

·            Define acceleration including its vector nature

·            Draw motion maps that include both velocity and acceleration vectors

·            Stack kinematic curves of position vs. time, velocity vs. time, and acceleration vs. time graphs

·            Know what each graph shows and what information can be obtained from each type of graph

·            Use the kinematic equations from x vs. t & v vs. t graphs

o   d = (average V)t

o   d = ½ at² + V_ot

o   V = V_o + at

o   V² = V_o² + 2ad

 

·            Analyze the motion seen in free fall and understand how uniform acceleration applies to a falling object

Here is a video I made which depicts free falling.

Unit Three: Kinematic Equations In Use

In class, we learned how to use the kinematic equations to find final velocity, initial velocity, distance, acceleration or time. The kinematic equations are:

d = (average V)t – "d, v, t" equation

d = ½ at² + V_ot – "dat vot" equation

V_f = V_o + at – "Vat" equation

V_f² = V_o² + 2ad – "Vad" equation

When you are trying to find a variable you look at your givens and based on what you already know and what you need to find is how you choose what equation to use. For example, if you are trying to find the average velocity and you are given the distance and time you use the d, v, t graph. You put the given variables in the equation then divide the distance by the time and you get the average velocity.

This how kinematic equations can be used in everyday life, today I had to pick up mangoes that had fallen from the tree in my backyard. While I was picking each mango, another mango fell (almost landed on my foot and if it had my foot would have hurt, just a little, but it would also have squashed mango on it) and I guessed how many seconds it took to fall and I measured the distance from which it fell from. The distance between the branch and the ground was 3.5 meters and the mango fell to the ground in about 1 to 2 seconds so lets say it dropped at 1.5 seconds. With the given variables I want to find out what the average velocity is. So I use the "d, v, t" equation with d = 3.5 meters and t = 1.5 seconds. The average velocity is 2.3 m/s. Which makes sense, I guess…..
Hereʻs my mango tree, I could not take a photo of a mango dropping so, yeah, here is my enormous tree that makes so much rubbish its not funny.

Unit Three: Acceleration so far.....

So far in physics, we've learned that acceleration is the change in velocity over the change in time. The units are meters over seconds divided by seconds (m/s^2). With acceleration we learned about three kinematic equations:

d = 1/2at^2+Vot

V = Vo+at

Vo^2+2ad

The variables are:

d = distance (x) (y) meters

V = final velocity m/s

Vo = original/initial velocity m/s

a = acceleration m/s^2

t = time s (seconds)

To be very honest I don't know much or understand much about the equations, but I do understand the difference between acceleration and force. Acceleration is as I stated above and force is not acceleration but the amount of power to increase the initial velocity and/or acceleration. I don't have anything to show acceleration other than a video I created to display the process I took to create one of my drawings. I accelerated the speed of the video footage so I could fit everything in it. So here's the video…..

Unit Two: Velocity

 
One of the three graphing rules is that "the slope of a position vs. time graph is velocity". In physics we use position vs. time to calculate an objects velocity using the distance traveled from the starting point over a period of time the object took to get from its origin to its current point/distance. The mathematical equation for the slope is V = d/t (V is velocity, d is the distance traveled, t is the period of time, in seconds, it took to reach that distance/position from the origin). Velocity is something we experience everyday either in the car, surfing or riding a seriously intense, "make you want to puke your guts out" ride at the Punahou Carnival. One ride, I think most people will agree with, is The Zipper. When we ride The Zipper, we are moving at a rate of 7.5 RPM (sorry I couldn't find how long the cable was so I couldn't calculate the distance or the time without having to include the revolutions). 7.5 RPM is the constant velocity of The Zipper after all the cars are filled and the ride starts. Once the Zipper starts, the cars rotate between 1 to 1.25 minutes in one direction. After the time period the ride stops for a second or two than starts moving again, the initial velocity is slower but gradually rises to the same velocity as before and period of time but in a different direction. So the drawing above is of The Zipper and next to the drawing is the variables V, d, and t, and the velocity.

Here are the variables, if you can't read it, it goes:

V=d/t

V=7.5RPM

d=18.75 revolutions

t=2.5 minutes 

Unit Two: Displacement

Displacement is the distance of the starting position from the final position of a point. In physics, displacement is used to determine points in position vs. time graphs and is one of the variables in the average velocity formula (V = d/t). When I take my dogs for a walk, the distance I walk is about 200 meters long. At the end of the walk I am in front of the gate to my house.  Since I am back where my starting point was at the beginning of the walk, the displacement is zero meters. Here is a drawing/diagram of my block and the route I take with my four dogs; the Shih Tzu (Baxter), the Maltese-Poodle (Zeus), the two bulldogs (the big one is Buddy and the smaller one with the big ears is Pebbles).

Unit One: Scientific Notation and Metric System

I know Mr. Blake (sorry, I know you didn't want me to put Mr. but there's Blake Lyon and that would just get confusing so yeah...) said no meter stick or yardstick so I went online and found this picture, which is kind of lame, but it works. So this is scientific notation where you turn really big or really small numbers, in this case big, into a smaller convenient value using exponents. In the picture, 8,900 is a little bit too big so by using scientific notation I move the decimal three digits to the left and since 8.90 multiplied by 10³  (10³ equals 1000) equates to 8,900. So the answer is 8.90 X 10³.We use this in physics, because we do a lot of conversions and sometimes the numbers are very lengthy or have many digits after the decimal point so by using scientific notation it provides us with simpler solutions to the conversion problems.

Image: http://www.kylesconverter.com/blog/wp-content/uploads/2009/09/scientific-notation-1.jpg

The metric system is convenient, because we have an easier time dividing and multiplying by tens when we need to calculate mass, length/height, and ext. The English measuring system is convenient for estimating the mass or height of something because we tend to find things easier by dividing things by halves instead of tenths. In physics, we use the metric system when we convert a kilogram to a meter instead of a ton to a pound. Because of the metric system measure by the power of ten the calculations and conversions are simpler. 

Image: http://gentlemansprivilege.files.wordpress.com/2009/12/metric-system-cartoon.gif

About Me...

My name is Alexis Sumiko Miyake, I'm Japanese-Okinawan and I live in Kahala. I am 4'11'' and play basketball, golf and I swim for the Punahou swim team. My favorite subject is art. I plan on going to either a film or art school after I graduate and then hopefully get a job at Pixar or Universal Studio's DreamWorks then go on to do my own solo work. So far I have learned how to animate both through technology and drawing (the same way they made Snow White). So pretty much my main drive in life is art. Next year I am taking four art classes so I can build up my portfolio for colleges. If that doesn’t work out I'll go into the fine arts or graphic design or just character design. So far in science I have taken Biology and Chemistry. Biology is not my strong suit but I liked Chemistry and got A's and B's. Honestly, the thing I really hope to get out of this course is a passing grade so I can get the credit. I also want to be able to say that I took Physics and I actually learned stuff. Last year I took Algebra 2/Trigonometry and this coming year I will be taking pre-Calculus. 

 The drawing above is a pen version of one of the two drawings I did for my Quality Project. I chose this drawing because I felt that it represented the side nobody really sees when they first meet me which is the artistic and more darker, serious  side of my personality. Another reason why I picked this over the other version was because this one was so much better looking.