ie-Physics

Experiment I-1

Of course change is a part of reality!  Without change life could not exist.  We observe a multitude of changes with our senses.  We take change for granted!  But when people stopped taking change (such as motion where an object changes its location) for granted, much was learned about our world.

1. It takes a finite time to cover any non-zero distance.  With an infinite number of points between any two locations, it is mathematically impossible to transverse an infinite number of points in a finite time.
2. The second argument is the famous Achilles paradox:  In a race between the fast Achilles and a slow tortoise, the tortoise is allowed to start some distance ahead of Achilles.  Achilles must first reach the location where the tortoise started.  But in the time Achilles is transversing that distance, the tortoise will have progressed a little further.  This reoccurs in each successive time interval.  Achilles must next transverse that new distance, but the tortoise continues to move beyond its location at the start of the time interval.  Achilles gets nearer in each successive interval, but never can catch the tortoise.
3. Consider that the tip of an arrow in flight in a space made of points must, at any given moment, be stopped AT some particular point in space.
4. Consider three parallel rows of points in space.  One set of points (B) remains fixed while A and C move in opposite directions at equal speeds.  But compared to C, A will have passed twice as many points as compared to B.  Therefore an instant of time can NOT correspond to the passage from one point to the next point.

But we observe the reality of motion through space.  So either our notion of space made up of points is in error, or the notion of motion is in error.  Trying to unravel these arguments led to new understanding that we call physics.  And in the process of developing the physics, we developed a civilization based on that physics far advanced from the world of the ancient Greeks.

Experiment

Because observing is the basis of all science, it is appropriate to start the study of physics with practice observing things that change.  We have all been observing since before birth!  So observation is not new to anyone.  But scientists have developed some habits that they believe optimize learning using observations.  These habits will be valuable whether you become the owner of your own business, a physicist, or just about any other vocation.

Get a notebook, preferably a bound notebook with pages sewn together, that you can make into your personal science journal.  Don't use loose scraps of paper which can get discarded or lost.  The purpose of your journal is to keep information forever.  Each page should be numbered.  Each entry should be dated and initialed or signed.  (Journals take on legal significance if you ever have to prove when you did something!)  Ink lasts much better than pencil, so use an ink that will be easy to read years in the future.  If you are not familiar with the information you should record in your journal, look at the screen on writing a formal report since much of the information needed for a formal report should be recorded first in your journal.

There are many methods of recording and studying motion and other things that change.  The author cannot know what equipment is available to you.  So you should consider the following as flexible suggestions that you can modify depending upon equipment, facilities and technology available.  You may have access to a digital camera and a personal computer, or a video tape camera, as well as more traditional rulers and watches.  Use the best suited available technology to gathering the needed data.

A digital camera attached to a computer works well for moderate motion in well lighted situations.  Video tape played back one frame at a time also works.  Photographic film with a strobe light works in the dark.  A ruler and clock are the least expensive, and often easiest technology!  And as you will find in Experiment I-2, with a little creativity you can often modify existing equipment to serve your needs.  When you are trying to learn new ideas, sometimes fancy technology is more confusing than helpful.  You be the judge what technology is best for you.

1. Measure and compare speeds of
   1. a moving person (your choice:  walking, running, crawling, rolling???), and
   2. several vehicles driving by.
2. To do so, measure distances for a number of marked locations.  (Distances could be measured and marked in the real world.  Alternately they can be measured on a monitor or photograph using image size or by a scale comparing a photographed object of known size with its image size.)
3. Record times passing each location.  (Time could be real time, perhaps in seconds, or by counting successive video frames.)
4. Construct several line graphs for each motion:
   1. displacement verses time.  The value for displacement at each time is the distance from the selected original location.
   2. speed verses time.
      Average speed (or velocity) is defined by v_av ≡ Δd / Δt
      where Δ, the Greek letter Delta, is used to represent the change in... ,
      Δd is the change in location called displacement, Δt is elapsed time.
      So the speed at each time is the distance covered in the previous time interval divided the the length of the time interval.
   3. acceleration verses time.
      According to Galileo Galilei, acceleration is a ≡ Δv / Δt
      So the value of the acceleration at each time is the change of speed in the previous time interval divided by the length of the time interval.
5. Consider the possible extent of error in locations and times, and the effects of possible errors on displacement, speed, and acceleration.
6. Ponder the limitations of your methods.  (e.g., what are the most outrageous measurements you might make?  What makes them outrageous?)

Finally, scientists often construct formal reports for others to read.  Communicating technical information such as observations and findings is another skill used by scientists but useful for most others.  If you need course credit, use your observations recorded in your journal to construct a formal report.  If unsure what details should be included, read the screen describing a formal report.  Make sure your report is based on YOUR personal observations and not copied from someone else.

Reference

• George Sarton, A History of Science: Ancient Science Through the Golden Age of Greece, Wiley, 1952.