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1st Proficiency

Problem:  What effect does the mass of a ball have on its force while rolling down an inclined plane?

Hypothesis:  I think that the greater the mass of a ball rolling down an inclined plane, the greater its force will be.  I believe this is because Newton's Second Law states that mass times acceleration equals force.  The greater the mass, the greater the force it will have.


  • Variables:
    • CV- slope angle of inclined plane, surface of ball, surface of inclined plane, wind speed, wind direction, surface of floor
    • IV- mass
    • DV- amount of force
    • Control- ball of no mass
  • Materials:
    • open space
    • wooden block
    • yardstick/tape measure
    •  ball of little mass
    •  ball of great mass
    •  inclined plane
    • scale
  • Procedure:     To begin my experiment, I gathered all of my materials.  Then, I set up my inclined plane, and placed a wooden block at the bottom of the inclined plane.  I then set barriers on each side of the inclined plane, so that the ball wouldn't roll diagonally somehow.  Subsequently, I turned on my scale, and weighed the two different balls to make sure that they were different masses.  Following that, I picked up one of the balls, and released it at the top of the inclined plane.  I watched the ball roll down, and hit the wooden block such a distance.  I later measured the distance the block traveled with a yardstick or tape measure, and recorded the data in a data table.  After that, I repeated the entire process two more times, because I realized that testing each ball three times would result in a more accurate result.
         Once the previous steps had been repeated, I decided to test the other ball in the same manner.  I released it from the top of the inclined plane, watched it hit the wooden block, measured its distance, and recorded the data.  I did that for a total of three times, and noticed that the results needed no more testing.  To conclude my experimenting, I organized all of my data in the data table into a bar graph.  Once that is done, my experiment is completely finished.

External Variables

     While I was doing my experiment, I consciously thought about eliminating all external variables I could possibly eliminate.  First of all, I tried my best to get accurate results by making sure the surface of the inclined plane was the exact same for every trial.  If the surface was bumped up or got changed while acting upon the experiment, accuracy would not have been an aspect in my experiment.  To make sure that the surface was always the same, I did a "check up" on the inclined plane after every trial.  This included me running my hand back and forth past the inclined plane and even blowing off any possible dust that could have landed on it.  By doing this, the surface of the inclined plane would be as close to perfect as I could possibly get it to be.
     Repairing the inclined plane's surface was a good way to eliminate external variables but there are other ways to do so.  Another way to eliminate them is by making sure the degree of slope is the same for every trial.  If it was different any time, then results would go awry.  To make sure the slope angle was always the same, I checked on the inclined plane's angle of slope with a protractor.  If it was different from the previous trial, I would modify it to match the degree of slope for the other trials.
     Wind can alter the results of an experiment, so I believe that it is necessary to eliminate that external variable.  The process to do so is very simple, for all I did is tested each trial inside where there is no wind whatsoever.  By doing this, the external variable of different wind speeds and direction is eliminated.

Results of Experiment

      Trial 1      Trial 2     Trial 3  Average
table tennis ball8.910.29.59.53
metal ball52.163.571.162.23
                   ***All numbers represent cm***
During this experiment, I was attempting to figure out whether  a ball of a larger mass would push a wooden block farther than a ball of smaller mass after rolling down an inclined plane.  I assumed that the ball with the larger mass would push a wooden block farther than the ball of lesser mass.  This is because Newton's Second Law of Motion states that mass times acceleration equals force.  Knowing this, a ball that holds a lot of mass would create more force than a ball with little mass when rolling down a constant inclined plane.  To experiment with this, I used a metal ball with a mass of 226.8 grams and a diameter of 31.75 millimeters, and a table tennis ball with a mass of 2.7 grams and a diameter of 40 millimeters.  The results clearly showed that the metal ball pushed the wooden block farther than the table tennis ball did, with an average of 62.23 centimeters of travel for the wooden block.  However, when the table tennis ball hit the wooden block in three different trials, the average distance that the wooden block traveled was only 9.53 centimeters.  As you may have already observed, my experimenting definitely supported my hypothesis.  In addition to the amount of mass effecting the wooden block's distance traveled, the density of each ball also effected the distance that the wooden block traveled.  The metal ball I used in my experiment was not hollow at all, and completely filled with a heavy metal.  On the other hand, the table tennis ball was hollow, and only surrounded with a thin layer of plastic.  Oxygen took place of the inside of the ball, which also made it lighter and less dense.  Overall, more mass definitely creates a larger amount of force when rolling down an inclined plane.

Meeting Proficiency

When thinking about this proficiency, many examples and ideas came to mind.  Newton's Laws of Motion apply to everything in the physical world.  There isn't one thing that is doing something on this planet that isn't dealing with any part of Newton's three laws of motion.  If the facts of what Isaac Newton stated in his laws of motion didn't exist, life would be unfathomable.

Newton's laws clearly apply to the physical world, as it is observed just in my experiment alone.  For example, the beginning of Newton's First Law states that any object at rest will remain at rest unless acted upon by an unbalanced force.  In my experiment, the wooden block was at rest until it was hit by the ball rolling down an inclined plane.  In addition, Newton's Second Law was also associated in my experiment, for he states that mass times acceleration equals force.  I was using different massed balls in my experiment, to decide which one had more force.  The ball with more mass altogether had more acceleration, causing it to have more force.  However, it is not only these two laws that apply to my experiment.  Sir Isaac Newton had three laws of motion, his third being that for every action there is an opposite and equal reaction.  At the instant the ball hit the wooden block, the ball's action, which was rolling towards the direction of the wooden block, was stopped by an equal and opposite reaction, which was the wooden block.  This caused both objects to move in the opposite direction, thus presenting Newton's Third Law.

Although Newton's laws of motion apply to my science experiments, it applies to everything in this world.  There are many examples of this, which will help illustrate my point.  The first law of motion talks about how an object at rest will remain at rest unless acted upon by an unbalanced force, and an object in motion will remain in motion unless acted upon by an unbalanced force.  I a person were to sit on a cart that was still, you would say that the person was at rest.  That person will remain at rest unless either pushed by something else, the cart is pushed, or other things included.  However, once that person on the cart is in motion, he will surely stay in motion until acted upon by an unbalanced force.  This could either be something stopping the cart or person or even something pushing the cart/person in a different direction.  Any of those options could be considered as an unbalanced force.

Furthermore, the second law of motion created by Sir Isaac Newton also applies to the physical world.  Everyone knows that a gun uses some form of bullet or item to release the end of the gun.  Gunsmiths probably endeavor to make their bullets as heavy as they can make them, without getting them too heavy.  If bullets were half of a gram in mass, people would barely feel it when they if shot upon.  At the same time, you would want to make it so that the rate of acceleration was at its highest possible, and its rate of deceleration at its lowest.  All of these factors could not be thought of if there were no truth to Newton's laws.

For every action, there is an opposite and equal reaction.  This is Newton's third law of motion, and applies to the physical world in numerous ways.  For example, when a rocket launches from the ground, it has an action that is opposed by the ground, which is an equal reaction.  A person standing on the ground is also an example of the third law of motion.  Gravity's force wants to pull the person down, but the ground is the opposite and equal reaction, which is keeping the person from descending underground.  As I have explained previously, Newton's Laws of Motion definitely apply to the physical world.

2nd Proficiency

Problem: What impact do different surfaces have on the time it takes a ball to roll down an inclined plane?

Hypothesis:  I believe that the smoother the surface is , the less time it will take for a ball to roll down an inclined plane.  This is because when a ball is rolling down a rough surface, it catches on to the tiny particles sticking out to slow down the ball.  Friction has much more affect on the ball when it rolls down a rough surface, and would easily slow down the ball.  When there is a smooth surface for the ball to roll down, the ball cannot catch on to anything, thus allowing it to roll down the inclined plane faster.  If it was rolling down a smooth surface, then there would be less friction to slow down the ball.  In other words, if there was a smooth plastic surface, a splintered wooden surface, and cloth-like surface, a ball would roll down the plastic surface the fastest.

  • Variables:
    • CV- type of ball, mass of ball, surface of ball, slope angle of inclined plane, person timing, length of inclined plane
    • IV- surface types
    • DV- time
    • Control- wood surface
  • Materials:
    • wooden inclined plane (preferably more than two feet)
    • cloth (at least length of inclined plane)
    • smooth plastic board (at least length of inclined plane)
    • ball
    • tape
    • ruler/ yardstick
    • stopwatch
  • Procedure:To begin experiment, gather all materials.  Then, set up wooden inclined plane at any angle desired within one and eighty-nine degrees.  After inclined plane is ready, turn on stopwatch.  Place ball on top of inclined plane, and start stopwatch once ball is released.  When ball reaches bottom of inclined plane, stop stopwatch immediately.  Record time it took for ball to roll down inclined plane in data table.  Repeat entire process until you feel that there are enough trials completed to be accurate.
  •            Tape plastic board on top of wooden inclined plane, or completely rebuild inclined plane.  Make sure that the angle of slope is still the same.  If the plastic surface is longer than the wooden surface, than mark spot at top with tape where the new start for the drop will, to make sure the ball's travel is the same distance.  Once new surface is set up,  repeat steps as were done with wooden surface.  In other words, time the ball while it was rolling down the inclined plane with new surface.  Make sure to record the times in data table.  Once these steps are accomplished, take down plastic surface. 
                 Subsequently, the goal is to test the ball on a cloth covered inclined plane.  Repeat second paragraph with few exceptions in next few sentences.  Tape cloth cover on top of wooden inclined plane, making cloth tight so the surface if flat.  The same rule goes with the part of marking drop spot if cloth is long than original inclined plane.  Record sufficient amount of times in data table, and convert data table into a column or bar graph.  Clean up area.  Once aforementioned step is completed, experiment is done.
      External Variables
      During this experiment, I endeavored to eliminate all external variables I could possibly could.  There were many ways in which I did so, and helped make my experiment be concise and accurate.  One way in which I consciously eliminated external variables was that I kept the same ball throughout every trial.  If the ball was a different surface in any of the trials, then the results would have been thrown way off.  For example, I hypothesized that the plastic surface would allow the ball to move faster down the inclined plane, but if I used a rough ball on the plastic surface and a smooth ball on the cloth surface, results would have gone awry.  In addition, the size and mass of the ball would greatly effect the speed of the ball rolling down the inclined plane.  Fortunately, none of these predicaments ever occurred because I used the exact same ball for every trial of every surface.
                  The size, mass, and surface of the ball would definitely effect my experiment, but what about the angle of slope?  My independent variable was the surfaces of the inclined plane, not the angle of slope.  If I were to change the slope angle while I was changing inclined plane surface, I would have two independent variables, not what I have displayed in the previous section of this proficiency.  In my mind, the cloth surface would make the ball roll the slowest (as you will also observe in the subsequent section).  However, if I were to make the slope angle steeper during the trials with cloth than during the trials with just wood, the results would be devastatingly inaccurate.  Therefore, the angle of slope have to remain constant during every trial in this experiment.
                The ball type and slope angle are significant to the accuracy of this experiment, in addition to the length of the inclined plane.  It is hopefully obvious that the longer the distance traveled, the longer the time it will take to reach the end.  In other words, if the length of the inclined plane is longer during the wooden surface trials than during the rest of the trials, then the end results wouldn't be scientific.  While I was experimenting, I made sure that for each surface the ball would always travel the same distance to reach the end of the inclined plane.  To accomplish this goal, I used the ruler, which was in the materials zone, to measure at what point the ball should start at so it would always travel the same distance every time. 
                Eliminating external variables is necessary if desired by the experimenter to have scientifically accurate results.  Fortunately, that was accomplished by me, which made my experiment that much better.
      Results of Experiment
                   Trial 1      Trial 2      Trial 3   Average
    wood0.70.70.8        0.73
    plastic0.50.60.6        0.56

            When figuring out whether different surfaces would effect the time it took a ball to roll down an inclined plane, I thought for sure that it would.  To experiment with this, I used an inclined plane with three different surfaces to put on it.  The original surface was a splintered wood, and there were also plastic and cloth surfaces.  In my mind, the plastic surface would allow the ball to roll down the inclined plane faster than on any of the other surfaces would.  My experimenting definitely supported my hypothesis, for the ball rolled much faster down the plastic inclined plane than on the other two surfaces.  After three trials, the average time that it took for a marble to roll down a cloth surface was 1.33 seconds.  While rolling on wood, the ball averaged to reach the bottom of the inclined plane in 0.73 seconds.  But when the plastic surface was put on the inclined plane, the ball could get to the bottom of the inclined plane in only an average of 0.56 seconds!  This is because friction slows down the ball, and is more effective on rougher surfaces,  for there is more area to catch on to the ball and slow it down.  The smoother the surface is, the less friction is effecting the ball.  Therefore, the plastic surface must be smoother than the other two opponents and altogether have less friction impacted on the ball.

            Meeting Proficiency

            Gravity and friction are two concepts that relate to each other in several ways.  Gravity's force to pull down items towards the Earth's surface is very strong, yet is opposed to by friction.  Air resistance is the main example of my reasoning now, and is a chief reason as to why items fall to the Earth's surface than at a vertical drop.  However, friction is involved with every action on Earth, and there is no way to avoid it unless inside a vacuum.  Friction is what restrains all objects from moving eternally, and having no deceleration.

            All things on Earth fall to the center of the Earth at a rate of 9.8 m/s/s.  However, this is not always the case, for friction comes into play and stops objects from maintaining that acceleration.  In the case of falling, air resistance is the real term, and slows down objects from moving in a certain direction.  The less friction is applied, the more the gravity will effect objects in falling.  Therefore, one another greatly effect each other for one relies on the other.

            3rd Proficiency

            Problem: What effect does the angle of slope have on the acceleration of a marble?

            Hypothesis: I think that the steeper the slope angle is, the greater the acceleration of the marble will be.  This is because there is more gravity affecting the marble while rolling down a steep inclined plane than if it were rolling down a gentle slope.  When there is more gravity affecting an object, it has a greater pull on the object, bringing it closer to the earth's surface faster.  In addition, any object falling directly downward towards the Earth's surface accelerates at a rate of 9.8 meter per second per second, or m/s/s. When the slope is steep, there is a less amount of force acting upon the ball.  The gentle slope causes a high amount of force to act upon the ball, not allowing the ball to roll down as fast as it would at free fall.

            • Variables:
              • CV- size of ball, mass of ball, length of inclined plane, surface, atmosphere, wind amount, surface of inclined plane
              • IV- slope angle
              • DV-acceleration of ball
              • Control- vertical drop
            • Materials:
              • protractor
              • 12 inch inclined plane surface
              • ball
              • stopwatch
              • yardstick/tape measure
            •   Procedure: 
            •      Gather all materials.Set up 12" inclined plane surface to a 30 degree slope.  Get stopwatch ready, and then pick up the ball over to top of inclined plane beginning.  Drop ball, and start timer when ball is released.  Stop timer when ball reaches the end of the inclined plane.  Record the acceleration of the ball while rolling down the inclined plane in data table.  Repeat this trial two more times. 
                   Change inclined plane angle to 45 degrees.  Start the stopwatch when ball is released from top of the inclined plane, and immediately stop it when the ball reaches the bottom of the inclined plane.  Record data in data table.  Repeat last two sentences of steps two more times. 
                   Change angle of inclined plane to 60 degrees.  Drop the ball at the top of the inclined plane, and start the stopwatch simultaneously.  When the ball reaches the bottom of the inclined plane, stop the stopwatch.  Record the acceleration into a data table.  Repeat this trial two more times.  Once all aforementioned steps are completed, create a chart from data in data table.  Clean up area, and then the experiment is completed.
            Results of Experiment

                Trial 1     Trial 2     Trial 3   Average
              ***All numbers under trials represent inches per second per second***

            In this experiment, I was wondering whether the angle of slope impacted a ball's acceleration when rolling down an inclined plane.  I believed that the steeper the angle of the slope was, the greater the acceleration would be.  My experiment clearly supported my hypothesis, because the sixty degree angle inclined plane allowed the ball to accelerate more than in any other slope, causing the ball to have a higher speed.  According to the results, the gentlest slope, or thirty degree slope, only allowed the ball to accelerate at an average rate of thirty-one inches per second per second.  The sixty degree slope let the ball accelerate at an average rate of 71.9 inches per second per second.  Based on this data, it is almost certain that the angle of slope greatly effects the acceleration of an object.  The reasoning as to why the slope angle does effect acceleration is because of several reasons.  First of all, all objects drop at a rate of 9.8 meters per second per second when in free fall.  When a slope is steeper, there is not as much of an obstacle than if it were to roll down a gentle slope.  If there are less obstacles in the way, gravity draws more affect onto the ball, thus making it fall faster with more acceleration.

            Meeting Proficiency

            Acceleration is the rate at which an object changes speed.  Right there is an example of how these two ideas relate to each other, yet also relate in many other ways.  When the acceleration of an object raises, it means that the speed of the object would also raise.  Speed is often altered by acceleration, and once an object is in free fall, the acceleration will never max out.  It is as simple as the fact that the higher the acceleration, the higher the speed.  The opposition is also true, for if the speed raises, the acceleration additionally raises.  Overall, speed and acceleration definitely relate to each other, and each one reacts similar to the other.

            4th Proficiency

            In the numerous simple machines I created, multiple types of energy were incorporated.  First of all, every single material I used in each simple machine started with potential energy, mainly gravitational potential energy.  However, once the first piece lost its potential energy transferring into kinetic energy, every part of the simple machines eventually gained some amount of kinetic energy.  However, although the kinetic and potential energy were varying among themselves, the mechanical energy remained constant throughout the entire process.  Mechanical energy is the combination of kinetic energy and potential energy, which there is always at least some of one energy always.  When a ball is moving, its potential energy that it had when sitting still is transferred into kinetic energy.  Therefore, if there is kinetic energy but no potential energy, or vice versa, there is still mechanical energy.

            The lever is a simple machine and uses mechanical advantage to transfer energy.  There are three different types of levers, the first-class, second-class, and third-class lever.  All three of them work in different ways, and use different amounts of mechanical advantage depending on where the fulcrum is positioned.  In the first-class lever, the fulcrum is placed between the load and the input force.  The input force is using kinetic energy on one side of the fulcrum to either lift of fling the load on the other side of the fulcrum.  In this way, mechanical advantage has been used to transfer the gravitational potential energy of the load into kinetic energy.  In the second-class lever, the process is slightly different.  The input force and the load are on the same side of the fulcrum, but the load is closer to the fulcrum than the input force.  Therefore, when the input force is using kinetic energy to lift the load, the load is not lifted as high as the input, but it allows the amount of mass of the load to be higher while using the same amount of force as it would in the first-class lever.  The load is transferring its potential energy into kinetic energy when the input uses kinetic energy.  The third-class lever has the least amount of mechanical advantage, for the input is between the load and the fulcrum.  However high the input goes, the load will always go higher.  However, the input force would have to be a lot more powerful than in the second-class lever to lift the load the same height.  Although the mechanical advantages are very different among the three levers, the way that they transfer energy is practically the same.  I need not say more about the third-class lever, for it would seem redundant to what I have aforementioned.

            Levers use mechanical advantage to transfer energy, in addition to pulleys.  In a fixed pulley, there are two sides of weight.  When one side has more gravitational potential energy than the other, it will lower and the other side will transfer into kinetic energy while rising.  This type of pulley has a mechanical advantage of only one, for each side must pull the same amount of weight as the other side to lift it.

            As well as a pulley, an inclined plane uses mechanical advantage to transfer energy.  However, the lower or gentler the slope is, the greater the mechanical advantage.  Any object sitting at the bottom of an inclined plane has potential energy, and is only converted into kinetic energy when pushed by another object using kinetic energy.  Although these types of energies are converting, the mechanical energy is still remaining constant, and will eternally.

            A screw is another simple machine that incorporates mechanical advantage to transfer energy.  Just like the inclined plane, the gentler the slope is, the higher the mechanical advantage will be.  The energy transfer while using a screw is exactly the same as an inclined plane, except  it spirals while ascending/descending.  While endeavoring to ascend up a screw, the kinetic energy of the traveling object varies, depending on the slope angle of the screw.  However, the transfer from potential energy to kinetic energy can be difficult if the angle of slope is very steep in the screw.

            A wheel and axel is a type of simple machine that utilizes mechanical advantage to transfer energy.  When the axel rotates, the wheel is also rotating in the same way.  However, since the wheel is usually larger than the axel itself, the mechanical advantage is greater because more torque is being created.  Whenever the axel is rotated, the wheel's potential energy is transferred into kinetic energy, and obviously spinning.  By doing this, vehicles and other objects like door knobs are able to work in their purposeful ways.

            A wedge is a simple machine, which would mean that it uses mechanical advantage to transfer its potential energy into kinetic energy.  When the wedge is still, it is stored with potential energy until it is moved somehow, transferring its energy into kinetic energy.  A knife is a great example of a wedge, for when a person is moving the knife, it is using its kinetic energy to either cut or slice an object.  In this way, it is using mechanical advantage to transfer its potential energy into kinetic energy, for the blade of the wedge of knife is longer than the point at which the hand is, causing it to be stronger than to cut an object with someone's own hand.  In other words, this mechanical advantage is being used to transfer a wedge's potential energy into kinetic energy.

            5th Proficiency

            Alternate Energy Forms

            Energy is the ability to do work.  Currently, the United States' main energy source has been petroleum, a nonrenewable resource that will eventually vanish from this planet.  However, there are many other forms of energy that the United States needs to continue utilizing.  Many of these alternate forms of energy include solar energy, geothermal, hydroelectric, nuclear power, and even tides from the sea.  With the use of these energy forms, costs will decrease greatly from the moment you use them, to when you have first begin to regulate these into your daily life, and will even be beneficial in the long run.  Utilizing these alternate forms of energy is vital to America’s ability to continue its innovation level, which is currently exceeding most other countries.
            There are multiples purposes for alternate forms of energy, but expenses seem to prioritize above all other aspects for American citizens.  It may or may not be apparent that alternate energy forms are cheaper from the start, yet they certainly do benefit people ultimately.  For example, solar panels are expensive at the payment, but they save more and more money as the days go on.  Petroleum, coal, and natural gas; three of the main energy sources in America, also high expenses for civilians every week, if not month.  However, with the use of alternate types of energy, people wouldn’t have to disburse wasted money for things that could be done much more efficientlyIn the United States, the average electric/gas bill is around one hundred dollars per month, which is obviously different from solar panels, which cost nothing at a timely rate.  Although some alternate energy forms may not work all the time, they do excel at completing work that is needed to be done. 
            Money is often an important aspect in American minds, but people can never forget about the condition of our world.  Currently, there are many machines and vehicles that use coal for fuel.  However, if one were to see the smoke arise from the smokestacks of a boat or factory, they might change their opinion about energy uses.  Pollution has been a major predicament in today’s world, and the amount of use of our coal doesn’t help diminish it.  In fact, many Americans this day feel that the air and even water pollution has gotten worse as the years go by, which is certainly not what most citizens want to hear or see.  On the other hand, if we were to start using wind, solar, and hydroelectric energy more frequently, the pollution level will decrease tremendously.  In addition, transferring energy from the tides of the oceans and lakes would cause no pollution, and humans need to begin using them more regularly to allow our country to succeed in the future.
            Alternative energy forms definitely benefit society by not polluting, yet they also are renewable for the most part.  The world will hopefully never run out of sunlight, and it is almost guaranteed that there will be some amount of wind eternally.  The point is that as long as these things will keep up, we will be able to utilize these forms of energy forever.  On the contrary, with the use of fossil fuels to create energy, society will eventually be desperate to change to some alternate energy source once the common one has vanished from the earth.  Subsequently, there will be little to no experience with that new energy form, thus creating a huge dilemma.  However, none of this would ever occur if alternate forms of energy became the status quo.
            When one imagines of how he/she can revolutionize the world, probability is low that he/she thinks of energy uses.  This is very unfortunate, because that is currently a key concern in today’s world.  There are many types of energy sources in the world, and it becomes inconceivable as to think of why we use the forms that we do.  It would be much simpler and more efficient to use wind, solar, hydroelectric, and other types of alternate energy forms than to use petroleum, coal, and natural gas for the United States energy needs.  Therefore, it should be high priorities for everyone in America to find ways to incorporate these alternate forms of energy to influence the United States energy needs.


            " Overview of Alternative Energy ." The Electronic Universe. N.p., n.d. Web. 28 Nov. 2010. .

            "Alternative energy - Wikipedia, the free encyclopedia." Wikipedia, the free encyclopedia. N.p., n.d. Web. 28 Nov. 2010. .

            "BibMe: Fast & Easy Bibliography Maker - MLA, APA, Chicago, Turabian - Free." BibMe: Fast & Easy Bibliography Maker - MLA, APA, Chicago, Turabian - Free. N.p., n.d. Web. 28 Nov. 2010. .

            "Free Fall and Air Resistance." The Physics Classroom. N.p., n.d. Web. 28 Nov. 2010. .

            "Free fall - Wikipedia, the free encyclopedia." Wikipedia, the free encyclopedia. N.p., n.d. Web. 28 Nov. 2010. .

            Karthik, Narayani. "Alternative Forms of Energy." Buzzle Web Portal: Intelligent Life on the Web. N.p., n.d. Web. 28 Nov. 2010. .

            "Lecture 8: Friction and Gravity." Physics Master. N.p., n.d. Web. 28 Nov. 2010. .