Unit 6 Forces

Pulleys can do a magnificent thing. They change the direction of gravity. 

Gravity is a force that naturally always pulls down. It is a force that exists only on the Y axis when it comes to two dimensional kinematics. 

Lets say spider man is hanging from a pulley. If you were to draw a free body diagram of the pulley on the roof top it would include: the force of gravity going down, Normal force (equivalent to the force of gravity) pushing up, and tension pulling to the left. Spider man's free body diagram would have the force of gravity down, and tension to the left. Now I know I said gravity will be altered and here it is: we must combine these two diagrams to find the net force, or the total force applied in the scenario. The tension from the pulley lies on the X axis, but the tension from spider man is on the Y axis. We cannot compare apples to oranges, so we have to make these two tensions some how equivalent. Imagine taking the free body diagram for spider man and rotating it clockwise. Now the tension is running along the Y axis where we want it to be so we can calculate the net force of the two objects combined. However, in turning the entire free body diagram the force of gravity that was vertical is now running horizontally. In essence, the gravity on spider man has a side ways pulls. 

Unit 6 Forces in Acceleration

This angel has two forces acting upon it. Weight pulls down because of the force of gravity. Tension is a force that pulls up from the angel because it is hanging from a cord attached to the ceiling. The cord is holding up the weight of the angel so there is tension on the cord. The angel is in equilibrium because the upward and downward forces acting upon it are equal. The magnitude of the weight is equal to the magnitude of the tension so the forces are balanced.
If the cord broke then there would no longer be a tension force, only the force of gravity. Then the angel would no longer be in equilibrium. The unbalanced force of gravity would cause it to fall with acceleration. If an object is accelerating then it is not in equilibrium. It can move with constant velocity and still be balanced (a=0) but if there is any acceleration then its unbalanced. 

Unit 5 More Newton

Today for unit five we reviewed Newton's three laws of physics. The first law is the Law of Inertia, that objects at rest (in motion) stay at rest (in motion) unless acted upon by an outside unbalanced force. The second law states that force equals mass times acceleration. The final law is that for every action there is an equal and opposite reaction. We use these laws to recognize the habits of an object's action and analyze it. For example these buildings are at rest and will remain at rest just like the first law says. Since they have a great mass it would take a lot of force, such as a devastating earthquake, to disturb their state of rest. This is how the second law explains the direct relationship between mass and force. However if the city were made of paper buildings (small mass) then a slight breeze could just as well disrupt the city. The buildings push down on the ground with a certain force and the ground pushes back with that equal force. If this did not happen, then the buildings would sink into the ground. This is like the third law because the buildings push down with a force, and the ground pushes back with an upward (opposite) force. These laws can also be represented in Free Body Diagrams. That is a diagram that illustrates what forces are present using vectors. This is a simple way to sketch the magnitude and direction of different forces such as tension, weight, and friction. These diagrams will come in handy when several forces are affecting an object. 

Unit 5 Newton's Laws

Newton's first law of physics is that an object in motion stays in motion and an object at rest stays at rest, assuming there are no other factors affecting the object. In this picture the boy running with the soccer ball is moving at a constant velocity with the ball. If he were to trip the ball would keep rolling away, that is because the ball is an object in motion so it will continue to stay in motion. Realistically though the ball will eventually stop rolling only because of friction against the grass and other contributing factors.

Newton's second law of physics is that force equals mass times acceleration (F=ma). This equation basically represents the relationship between force and mass and acceleration. Let's say the boy in white passes the ball to the boy in blue and he kicks it into the goal. The ball has a mass and acceleration and so does the swing of the boy in blue's leg. In order to make a good kick his force must be stronger than the force of the ball that is passed to him. Lets say the soccer ball is really heavy like lead. If it were passed to the boy in blue its force would overpower the boy's kick and he would not be able to kick the ball.

Newton's final law regarding physics is that for every action there is an equal and opposite reaction. In the picture above this is represented in running. The back leg pushes back against the ground in order to push the body forward and run. Or the wind back of a leg to make a powerful kick. So whenever an object pushes another option it gets pushed back (opposite direction) with equal force. 

Unit 4 Diagonals

As we have been learning about projectiles in unit 4, the X and Y axis must be handled separately when it comes to 2D kinematics. We have been trying to understand this contradicting rule by applying it to simple scenarios. For example, a ball rolling off of a table. The ball rolling is represented by the X axis and once the ball rolls off the table, the falling downward takes places on the Y axis. It is easy to separate the two axes for this situation. Today, we stepped it up to a more complex level involving diagonals. It is harder to see the distinction between X and Y axes in diagonals so you have to treat the diagonal like a vector. A vector is a straight line whose length is magnitude and whose orientation in space is direction. They are usually represented by arrows. By breaking the diagonal vector into any two other vectors you can create a right triangle. As long as the two vectors start and end in the same place, they are equivalent to the diagonal. This places clear vectors running along the X and Y axes that are easier for us to use. The diagonal acts as the hypotenuse and the other vectors are now opposite and adjacent to the diagonal. For example, the slide in the picture above would be the diagonal that we try to break up. The ground underneath the slide is the vector on the X axis and the ladder leading up to the slide is the vector on the Y axis. You can use these sides in trigonometric functions (sine, cosine &tangent) to solve for velocity on the X or Y axis. And that is how you break down a diagonal in 2D kinematics.

Unit 4 2D Kinematics

Today we applied our knowledge of one dimensional kinematics, and figured out how to do 2D kinematics. 1D kinematics only involves one axis, so a ball rolling across the floor or a car driving only involves the X axis. Dropping something from a balcony or tossing a ball up in the air only involves the Y axis. However if the car were to drive off a cliff, or you played catch with a friend, two axes come into play. The key to handling 2D kinetics though is to always remember that the two axes are independent of each other. They do not affect each other. It's hard to wrap your mind around but consider this: in the picture above my friend and I, on the left, will hit the water at the same time as the boys on the right if we jump at the same time from the same height. Even though we jumped straight down and they ran out for a farther jump, we all landed at the same time. We all have the same Y variables or distance, acceleration, and velocity, only our X variables vary. In terms of the X axis we have 0 displacement, while they land out a couple meters. Also, we have no acceleration on the X axis, but they do because they ran and jumped. Time is a function of the Y axis, and our Y axis are the same so we land at the same time. The variation of X axis does not interfere with the Y axis, thus does not affect the falling time.

Summary of Quarter 1

Unit 1 was an introduction to physics. We began by developing a thorough understanding of metric measurements and how to convert these units. A few common graphs were also introduced to us. We learned how to identify the relationship of the graph, what is going on in terms of motion, and how to represent each graph with an equation. Once this basic knowledge was established we applied it in the following units.

Unit 2 was about Kinematics, or the study of motion. This called for a lot of graphs. We learned how to convert a position vs. time graph into a velocity vs. time graph, and the other way around. By comparing both of these graphs we could really analyze the motion of the object. We could look at what was going on with distance and velocity at the same time to see how they were related. We also began solving simple word problems with the new equation d=vt, that is distance=average velocity multiplied by the time.

In Unite 3 several new equations came in handy. We learned about acceleration, an addition to kinematics, and applied it in our new equations.  I learned that the acceleration of gravity here on earth is 9.8m/square second. With our three new equations we could solve word problems to find distance, velocity, time, or acceleration. This applied to several real life situations, such as a moving vehicle, dropping something, or throwing something.

This quarter I learned about the technical differences in scientific vocabulary. Before I would not have known the difference between speed and acceleration. Nor would i have recognized scalar values apart from vector values. Most importantly, I learned how deceiving motion can be. Who knew that to stop accelerating in one direction, you actually have to accelerate in the opposite direction. Or that two objects fall at the same rate regardless of mass. Or when a ball is tossed up into the air it undergoes several changes in velocity, but has the same acceleration the whole time. And it is accelerating in the same direction even though it goes up and down. Tricky tricky.

Unit 3 More Acceleration

This grass hopper faces constant acceleration when it is jumping. The force of gravity is always pushing down on it, so when it jumps it is always jumping against this force. When it winds its back legs and leaps it leaps with a great velocity. As time goes on the downward acceleration slows down the velocity of its jump. Eventually causing the velocity to be zero, this is the climax or peak of the jump. After this, the grass hopper begins to fall with a negative velocity, but still the same downward acceleration of gravity. Since it is now  falling with gravity and not against it, the grass hopper picks up speed. The velocity at the end of the jump, right before landing on the ground, is the same amount of velocity that the grass hopper jumped off with. So the velocity undergoes several changes, from fast, slow, stop, start up slow, and then finish fast. The acceleration, however, remains constant the whole time because gravity is not changing.

Unit 3 Acceleration

Today we were introduced to acceleration. Acceleration is the change in velocity divided by the change in time. It basically is a change, either increase or decrease, in speed. If the speed is constant, or there is no speed, then there is no acceleration. For example when you first get into a boat and are not yet moving, you are not accelerating. Once you start the boat and go you are accelerating from zero. This is a picture of a boat that used to be behind us. Then their rate of acceleration increased while we maintained a constant speed (no acceleration) and they passed us. In the end, we all accelerate down for the no wake zone and then even more when the engine is turned off and the boat ride is over. At that point we have no acceleration again just like we started. 

Unit 2 Kinematics Again

This plane is moving through the air in a certain direction at a certain speed, but it will not remain at the same speed all the time. For example, the instantaneous velocity at lift off and landing will vary. So an average velocity can be calculated as the change in displacement over the change in time. In regards to these three variables, if at least of the two variables are known, the third can be calculated.  

D=VT

 That is how pilots predict the length of their journey. All they have to do is divide the distance of their destination by their average velocity to determine how long it will take to get there.

Unit 2 Kinematics

This red car is rolling swiftly down the hill. Since this car has values that can be measured with magnitude and direction it is called a vector. Some examples of vector measurements are displacement, or distance traveled in a certain direction, and velocity. The velocity, or speed in a direction, of the car will naturally accelerate as it goes down the hill. Acceleration is a change is speed or direction. When it reaches the bottom of the hill the acceleration will be zero because velocity will be constant, or unchanging. That is assuming the driver maintains a stable speed limit and doesn't hit the gas or slam on the breaks. The slope of a constant acceleration is zero and on a graph it would be represented by a flat horizontal line. 

Unit 1

Thanks to physics, this fish is able to float. When the fish breaths in the oxygen produced by the filter its buoyancy increases. The buoyancy pushes the fish upward and gravity pushes it down. So by adjusting the volume of oxygen inside itself it can manipulate its density, defy gravity, and float. Volume is a derived unit, meaning it is based upon base units. The volume of this fish tank is 626,340 mL. I measured this with metric units because the metric system is an easy way to take measurements. It is a standardized system and can be easily converted to another metric unit. 

self introduction

My name is Kimberly Nicole Brown. I am the middle child of three girls and just turned 17. I like science because I think its interesting how it really does apply to everything around me. I also like how its a constantly growing knowledge. I have recently been getting into surfing. I am still a beginner but i just bought a board which is the first step. I am interested in a counseling career. I like to cook and i love roller coasters and the beach. I have taken Biology and Chemisty and gotten good grades for them. I just finished geometry and will be taking Alg 2 Trig this year. I hope to learn what physics really is. I know it has to do with movement and motion but that vague information is all I really know. I hope to learn interesting things that I can use to predict natural outcomes of given situations and understand how things work.