Contents: measurement, units, significant digits, unit conversions, scientific method. And a course overview.
Write down your name, what science and math you’ve had, what your future educational plans are.
DERIVED UNITS & CONVERSION FACTORS:
Write down your name, what science and math you’ve had, what your future educational plans are.
Assign homework and reading. Chapt. 1: 4, 8, 10, 16, 18, 20, 24. Read chapter 2.
TODAY: measurement; units; scientific method; sig. Digits; unit conversions.
What is a MEASUREMENT?
A measurement is a quantitative observation. The observation must be expressed as a number, the number must have some unit.
Tell me about a measurement you made today. (examples: did you measure a time? Temp? speed?) (you didn’t look at your speedometer?) How can you measure the speed of a car as it passes you when you are on the side of the street? (prep for next chapter).
Physical science as detective work, because it’s based on observation and theory, and arguments for or against the theory are based on the observations. Here is an observation: a car in front of you turned right off 28th onto Cherry at 12:28 pm. Let’s say whoever it was turned too fast, without signaling. Depending on how much you know about cars, you might observe what kind of car, color, year. These are quantitative observations, although color is not very precise (not a number). Do you like that car, year, color; were you slightly perturbed that the driver turned so fast without signaling? That’s qualitative—maybe means something in a social science setting, but not physical science. Qualitative evidence may be used in court if motivation for a crime is being considered, but the physical evidence, if there is any, is most important.
Probably you didn’t use the metric system for any measurement you might have made recently. So right away, physics/physical science is somewhat foreign to you. Because you come in here and find (will find) that meter sticks measure length and kilograms and grams are used to measure weight. US is only country not using it. Committed to it in 1975, but without a timetable or deadline
You need UNITS in order to make a measurement. You can have a system of units you chose yourself—if you lived as a hermit in the woods, you might have to. What kinds of things do you need to measure? LENGTH—to build something, such as a cabin to live in. TIME—to consistently boil an egg to a desired state. MASS or weight—seems less important. Can you think of any examples where the hermit would need to know weight? Again in cooking, may be important. Or the hermit might want a system to measure his own weight. Could use pebbles from the creek that are about the same size. Maybe he weighs 250 pebbles, wants to lose 20 pebbles.
Possible standard units for the hermit: His walking stick = standard length. Pebbles of approximately same size=standard of weight (not very accurate). Dripping water from a coffee can with small hole=time. Very much lacking in precision, but he’s technologically lacking. And what about the hermit’s neighbor, when he tries to tell him how big a fish he caught? Maybe the neighbor uses different sized pebbles! Well, he’d hold out his hands, probably, to show how big the fish was, so they’d both understand without reference to standard pebbles or a walking stick unit. |
What are the real STANDARDS used in science and industry for length, time, mass? A STANDARD is a fixed, reproducible value that enables accurate and precise measurements to be taken. It’s what allows quantitative observations to be made. Metric system or mks system of units is defined in the following way:
LENGTH: the measurement of space in any direction. The standard of length is the METER, defined as the distance traveled by light in empty space in 1/299,792,485 sec. The speed of light can be used because it’s a universal constant.
MASS: the amount of matter an object contains. Standard of mass is the KILOGRAM, which is the amount of matter in a platinum-iridium cylinder kept at International Bureau of Weights and Measures in Paris. US has one of these bars also, at NIST headquarters in DC.
TIME: other names for it are duration, period, and interval. The SECOND as a standard is well-defined: “the duration of 9,192, 631, 770 cycles of the radiation associated with a specified energy-level transition of the cesium-133 atom.” Einstein and simultaneous events, the last hurdle he jumped in creating relativity. Time on your own watch as observed by you does not increase or decrease.
DERIVED UNITS & CONVERSION FACTORS:
Derived units are so-named because they’re derived from the fundamental units. Area and Volume are both derived from length. These are the ones we’ll use in tonight’s lab.
Another derived unit is speed or velocity, which uses the fundamental units of length and time. We’ll use it in a later lab, but you measure it all the time, by looking at your speedometer.
You’ll also be using a conversion factor in the lab, converting from meters to feet.
SIGNIFICANT DIGITS: Will discuss next time, after you have some experience making measurements.
SCIENTIFIC METHODOLGY
Basically, it’s all theory and experiment. Scientific methodology is observation/hypothesis/prediction tested by experiment. An experiment is a reproducible set of measurements. A hypothesis becomes a theory if it has been around long enough and passed all imaginable experimental tests many times. Example: the atomic theory of matter. A law is different from a theory. A law is a concise statement in words or in a math formula about a fundamental relationship of nature. Examples: F=ma. E=mc^2. The law of energy conservation.
Scientific attitude is mainly curiosity combined with healthy skepticism, a willingness to accept scientific ideas but not to become too attached to them. Not about ultimate reality—that is more personal than science, and beyond the realm of science too.
Course overview: Basic physics and chemistry, plus some of their applications in fields such as earth science and astronomy.
Motion is the most basic thing in physics, because without it, there’s no need to worry about space and time. Motion is even important in why things feel hot or cold—motion of molecules constitutes what we call heat.
Different types of motion result from different forces acting on objects, as described by Newton’s laws of motion and of gravity. Another way of describing motion is in terms of energy. Energy offers an explanation of WHY motion can exist, predicting when it will happen, "how much" motion, and what is accomplished by the moving object(s). However, energy itself is inexplicable except as the “capability of doing work.” Things get done in this world because work is done, using available energy supplies.
The rest of the course is about how electrons, protons, neutrons, atoms, molecules and light (electromagnetic radiation) all interact as a result of forces, energy and work. So the big three ideas of this course are FORCE, ENERGY and WORK. The FEW ideas you can use to describe as briefly as possible what this course was all about.
