Charge Transfer and Interaction

How did the balloon become negatively charged when rubbed on my hair?

Most everything starts off neutral. When I rub the balloon on my hair, my hair sends electrons to the balloon. The balloon gains electrons and becomes negative while my hair loses electrons and becomes positively charged. 

How does the balloon attract neutral water? 

The hydrogen atoms are positive while the oxygen atoms are negative in a water molecule. The water molecules realign themselves to put the positive towards the negatively charged ballon. The molecules are now polarized, or separated. The stream of water alters it path closer to the balloon as it is attracted to it due to opposite charges. 

Projectile Motion lab

In order to demonstrate rpoject motion, we threw a basketball in the air. We videotaped this motion using video physics, and we plotted points along the flight path of the basketball. We were then able to creat graphs with which we examined the projectile motion of the basketball. 

Graph of x velocity 

Mh linear fit equation was y= -1.740 x+ 3.424. Since the slope is relatively close to 0, it is a horizontal line. Since the slope is 0, the acceleration is 0 in the x direction. The object is moving to the left because the velocity is negative. There is no horizontal force, so it is traveling at a constant speed horizontally. The equation is Vx(t)= Vxi. 

Graph of y velocity: 

My linear fit equations was y= -11.336x + 5.245. When the velocity is postive, it is slowing down and moving upward. At Vy= 0, it turns around, and speeds up moving downward due to the negative velocity. The velocity of y is constantly changing with time. The slope is the acceleration due to velocity. 

The equation is Vy(t)= -10m/s2t + Vyi. These graphs always have a slope of -10m/s2 and are never curved. 

Graph of x:

My linear fit equation was y= 2.746x + .089. The slope of x vs t is Vx. The object is moving in the t direction and rightward. The equation is x(t)= Vxt+ Xi. These graphs are never curved because velocity is constant. 

Graph of y:

The equation of my linear fit line was y= 1.139x + .587. The graphs for y are always curved as it demonstrates the flight path. The equation is y(t)= (-10m/s2) t2 + Vyit +Yi. 

Forces in Two Dimensions

• How do we analyze forces in 2-Dimensions?                                                                         We can analyze forces in two dimensions by analyzing each dimension separately. We use the x or horizontal dimension and the y or vertical dimension. In order to analyze the dimensions separately, we can use trigonometry. We use fx= F cos theta and fy= f sin theta. You get the net force for each dimension when you add the vertical and hortizontal components separately. 
• How do forces cause objects to move in a circle?                                                   Centripetal force is any force that causes and object to move in a circular motion. The centripetal force is a center-pointing net force, which causes the object to move in a circle. The object can move at constant speed, but it is constantly changing direction. 
• What does it mean to be in orbit? How do satellites orbit planets? How do planets orbit the sun?                                                                                                                                           To be in orbit means that one object is on a continuous elliptical path around another object in space. Satellites orbit planets because an object will stay in motion unless and unbalance force acts on it. The force of gravity pulls the satellite towards the earth. The satellite is actually falling around the earth because as the earth curves, the satellite curves. It must be in orbital velocity. Planets orbit the sun because of the centripetal force of gravity that comes from the sun. There is no other force in the solar system to keep them from orbiting. The earth orbits at a constant speed, but it is accelerating because the direction of it's velocity is constantly changing. 

King of the Hill

Standard 1: Experimentation

After we thought our first car was done and we tested it out, we realized we were going to have to do a lot more experimenting in order to get it to work. Our first car didn't move at all, so we decided to change a lot of things. This experiment taught us that the body of our car was probably too heavy and that was part of why it wasn't moving. We realized that our wheels needed more mobility for the car to be successful. We added straws over our wooden skewers to let the wheels move around something. We also cut down the body of our car, a cardboard box, to make it lighter. The body of the car then became a flat piece of cardboard. 

Our finished car: 

Standard 2: Quantitative Analysis

We used the forced probe and the theory of gravity in order to determine the mass of our car. Our results from the force probe are shown in the picture below. We used the force to discover the mass by putting it into Fg=mg. From this we got that the mass of our car was .0028 kg which we converted into 2.8 grams. 

We then used video physics and graphical analysis to find the acceleration of our car on a flat surface. Our graph looked like this: 

We determined our acceleration to be 7.188 m/s squared as that was the slope of our line. We could use the slope to find acceleration because it measured the change in velocity over the change in time, which is acceleration. From there, we calculated the net force on our car using Fnet= mass times acceleration. Our equation was Fnet= (2.8g) (7.188m/s2), so we found our net force to be .0201 Newtons. 

Standard 3: Qualitative Analysis

Conservation of energy says that energy can't be created or destroyed, and it only changes for,. Tjis explains the movement of our car from the bottom of the hill to the top because our car has elastic potential energy or Us from the balloon at the bottom.  As the air is released from the balloon, the energy is changed into kinetic energy, and the car makes it to the top of the hill. Once the car makes it to the top of the hill, some of the energy changes into gravitational potential energy or Ug as the car is at a height, yet it also still has some kinetic energy as it keeps moving. The car only has kinetic energy as it goes down the hill, and once it stops moving it changes back into potential energy. The energy of our car was never destroyed as it only changed forms.

Conservation of momentum says that the momentum before the collison is equal to the momentum after the collison because the total momentum is constant. The combined momentum of our car and our oppoenent's car was the same after the collison as before it. The momentum stayed constant. In other words, the momentum gained by one car was equal to the momentum lost by the other car, which caused the total momentum of both objects to stay constant. 

Newton's Laws

Object: Battery buggy 

Constant motion: Newton's first law states that an object at rest will stay at rest, an object in motion will stay in motion with the same speed and direction unless an unbalanced force acts upon the object. When the battery buggy was off and at rest, it stayed at rest unless it was pushed by someone. When the battery buggy was on, it stayed moving in the same direction and same speed unless we stopped it or added extra force by pushing it. 

Change in motion: Newton's second law of motion says that the acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. This is shown in the equation F=ma. When the battery buggy was on and moving at a constant speed, the net force was changed when I stopped the car. By stopping the car with my hand, I added an unbalanced force on the buggy. I changed the acceleration and therefore changed the net force. 

Action-reaction force pair: Newton's third law says that for every action pair there is an equal and opposite reaction pair. The reaction pair is the same in magnitude and type yet opposite in direction. The table and the battery buggy were an action-reaction pair. The normal force of the battery buggy pushed down on the table and the normal force of the table pushed up on the battery buggy. The normal force on these objects was the same magnitude but a different direction since they are action-reaction pairs. 

 

Friction Lab

Big questions: What is friction? How does it relate to the atomic description of the universe? 

How does static friction differ from kinetic friction? 

How we went about investigating the big question: For this lab, we used a shoe to demonstrate the force of friction. We took the mass of the shoe using a force probe. We then placed the shoe on the table and hooked the force probe onto it. We added brass masses to the shoe, and we slid the shoe across the table. We then recorded the force of static and kinetic friction. The maximum force of the peak on the force probe was the static friction, and the mean of the straight line on our force probe was the kinetic friction. We then analyzed our data by graphing the weight of the shoe vs. the static fiction and the weight of the shoe vs. the kinetic friction. We created equations from the forces of kinetic and static friction. 

Answer to the big question: 

Static friction is present when both objects are stationary. It must be overcome to start an object's motion. Kinetic friction is present when one or more of the objects are in motion. Must be overcome to keep an object moving at constant velocity. In the force of friction, the electrons are on the surface and the force must overcome them. The friction increases for rougher surfaces. In this case, friction depended on the shoe's surface and the surface of the table. The coefficient of static friction is always greater than the coefficient of kinetic friction. Slope was the coefficient of friction, which we represented with "Mu."

The equations were: Ffs= "Mu"s Fn

                                Ffk= "Mu"k Fn 

    

Evidence to support conclusions: Slope was the coefficient of friction for our lab. Our data supports the fact that coefficient of static friction is always greater than the coefficient of kinetic friction. Our slope for static friction was .702, while our slope for kinetic friction was .647. 

How I can used what I learned in a new situation: I can use the equations we found for the force of kinetic friction and the force of static friction in other situations. I can use it to find how much force it takes to get an object moving and to keep it moving. I can also use it to find the coefficient of friction, using normal force. 

How this relates outside of class: A real life example would be a hockey player hitting the puck across the ice. The ice has less friction than asphalt would, but it still has so,e friction. at a certain point the puck will come to a stop due to this friction.          

Collision Lab

Big question:

What is a better conserved quantity in a collision- momentum or kinetic energy?

How we went about investigating the big question:

For our lab, we placed two range finders on a track and used two cars. We then conducted two different collisions. For the elastic collision, Weser the carts up with their spring launchers facing each other, and we then pushed the red car to collide into the blue. We recorded the speed of the carts before and after the collision. For the inelastic collision, we set the carts up with their Velcro sides facing so that they would stick together. We again pushed the red cart towards the blue and recorded the speeds of the carts before and after. 

Answer to the big question:

The answer to the big question was that momentum is the better conserved quantity in a collision. 

Evidence to support answer: 

We used  % difference = [(TOTAL ENERGY_AFTER - TOTAL ENERGY_BEFORE)/(TOTAL ENERGY BEFORE)] x 100% to find the amount of energy that left the system. We then used  % difference = [(TOTAL MOMENTUM_AFTER - TOTAL MOMENTUM_BEFORE)/(TOTAL MOMENTUM BEFORE )] x 100 to find how much momentum left the system. We got the following results: 

 For the elastic collision 7.86% difference of momentum lost was less than the percentage lost for the kinetic energy. In the inelastic collision, the 22% of momentum lost was less than the percentage lost for the kinetic energy as well, so in both collisions momentum was better conserved. 

How I can use what I learned in a new situation: 

I can use the equations for percent difference to figure out how much energy or kinetic energy is lost. I can also use the conservation of momentum theory to plug in and find other values such as velocity.

How this relates outside of class:

This relates to the Large Hadron Collider, which is a particle accelerator. Two high energy particle beams are guided around the tube by electromagnets. The magnets are used to squeeze particles together and increase the chances of collision. This relates to the amount of energy and momentum that is needed in order for the particles to collide.