Physics, chemistry: closed system vs isolated system

Tutoring physics or chemistry, definitions are always important. The tutor compares closed system with isolated system.

A closed system cannot lose or gain matter; it cannot exchange matter with the surrounding environment.

An isolated system is closed as above, but also with regards to energy. That is to say, an isolated system cannot exchange matter or energy with the surrounding environment.

Source:

Giancoli, Douglas C. Physics, 5th ed. New Jersey: Prentice Hall, 1998.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Physics: relativistic mass

Tutoring physics, relativity may arise. The tutor mentions its application to mass.

Einstein postulated, in his Special Theory of Relativity, that effective mass increases as velocity does, according to

m=mo(1-v2/c2)-0.5

where mo is the rest mass, while c is the speed of light.

The rest mass of an electron is 9.11×10-31kg. If travelling at 80.0% the speed of light, or 0.800c, the electron’s mass will be

m=9.11×10-31(1-(0.800c)2/c2)-0.5

which gives

m=1.52×10-30kg

or 1.67 times its rest mass.

Source:

Giancoli, Douglas C. Physics, 5th ed. New Jersey: Prentice Hall, 1998.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Science, Climate change: the albedo effect

Tutoring high school science, you may be asked about the albedo effect. The tutor explains it simply.

Albedo means loss of incoming radiation due to reflection. Light and heat are examples of radiation (see my previous post).

Regarding Earth’s climate, the albedo effect refers to the idea that sunlight that reflects from Earth doesn’t heat it. The greater Earth’s albedo, the less heat Earth absorbs from the sun. If Earth’s albedo decreases, it will absorb more of the sun’s rays, so will heat up. This is the simple way of applying the albedo effect.

Polar ice caps, covered in white snow, are quite reflective. However, as the ice caps melt, they expose rock and ocean, which are potentially much less reflective. Hence, Earth’s temperature could rise from the melting of the ice caps because of a corresponding reduction of the albedo effect.

Source:

www.universetoday.com

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Science, physics: what is radiation?

Tutoring science, the concept of radiation arises. The tutor explains it.

Radiation is electromagnetic energy travelling from its source.

Imagine a radio receiver which you can tune to any frequency. Actual radio station signals will be at the low end, then microwaves, then heat (aka infrared), then visible light. Past visible light is ultraviolet light, then X and gamma rays.

Radiation of higher frequency has higher energy. X and gamma rays have such high energy they can pass through solid objects.

Source:

nasa.gov

symmetrymagazine.org

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Physics: definitions of stress and strain

Tutoring physics, you might encounter the concepts of stress and strain. The tutor defines them.

In physics, stress and strain are related, but have very different meanings. A helpful idea is that stress is imposed on an object, while strain measures its reaction.

stress noun:
the force per unit area applied to an object. In this context, the object is likely not mobile; therefore, the stress likely has the effect of changing its shape, possibly not permanently.

strain noun:
the change in length the object experiences (resulting from the stress), divided by its original length. An object compressed from 100.cm to 90.cm experiences a strain of -10./100., or -0.10 (aka -10.%).

Source:

Giancoli, Douglas C. Physics, 5th ed. New Jersey: Prentice Hall, 1998.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Physics: what does elastic mean?

Tutoring physics, the term elastic can surface. The tutor discusses it.

elastic adj:

able to recover its original shape; able to resist permanent deformation after a distorting force is withdrawn.

Referring to a rubber band, it’s not called elastic because it stretches, but rather, because it tends to regain its original shape after the stretching force is released.

Source:

Giancoli, Douglas C. Physics, 5th ed. New Jersey: Prentice Hall, 1998.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Cooking: temp of a warm object

Cooking means constant self-tutoring. The tutor speculates about the actual temperature of a warm object.

Yesterday I took a glass casserole dish of mac and cheese from the oven. Its baking temp was 177C.

An hour later, most of the mac and cheese had been served from the dish. Moving it, I was surprised how warm it still was to the touch.

Yet, how warm was it? I didn’t have a convenient way of measuring, so I opened a browser tab and found rc.rynryder.com, whose members seem to agree that about 60C is dangerous to touch for more than a second or two.

The casserole dish wasn’t hot; rather, just surprisingly warm. I’d estimate it was about 40C.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Math: how far away is the goose?

Tutoring math, you notice that people like relatable examples. The tutor brings up his observation of a Canada goose.

Looking out over a lake in Nanaimo on Sunday morning, I saw an exceptional Canada goose swimming apart from the others.

The setting was so tranquil, even distance seemed irrelevant: I felt that, on a whim, I could suddenly scoot down to the water, plunge in, and join the goose if I wanted. Yet, how far away was it, really?

Holding my phone at 20cm, or 200mm, I observed the goose at about one-sixth of my phone’s lens port, which is 7mm across. So, to me, the goose appeared 7/6=1.17mm. Yet, a goose that prosperous would likely be about 60cm, or 600mm, from tail to breast. From optics,

object distance/image distance = object length/image length

Therefore,

d/200 = 600/1.17

Multiplying both sides by 200, we get

d=200(600)/1.17 = 102574mm or about 103m

Source:

Bull, John and John Farrand, Jr. The Audubon Society Field Guide to North American Birds, eastern region. New York: Alfred A. Knopf, 1977.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Astronomy: meteor, meteoroid and meteorite: what’s the difference?

Tutoring science, meteors and their kin might arise. The tutor defines meteor, meteoroid, and meteorite.

A meteor is the streak of light you might see in the sky at night, when matter travelling through space enters Earth’s atmosphere.

The rock, or whatever matter arrives, is typically travelling at high speed. The air friction it encounters in the atmosphere heats it up, usually to evaporation – but not always. However, it gets so hot it glows, which is what you observe.

The object itself, arriving in Earth’s atmosphere and glowing, is a meteoroid.

Any part of the meteoroid that lands on Earth’s surface becomes a meteorite. As I understand, meteoroids rarely manage to become meteorites.

hubblesite.org

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

Calculator usage: horsepower to kilowatts on the Casio fx-991ES PLUS C

Tutoring physics, you face unit conversions. The tutor shows how the Casio fx-991ES PLUS C can be used.

Inside the cover of the Casio fx-991ES PLUS C, at the bottom, is a list of unit conversions. Specifically, it indexes each conversion with a number to which the calculator refers. You’ll see, for instance,

29 hp→kW

which means that 29, entered within the conversion context, performs horsepower to kW.

Example: Using the Casio fx-991ES PLUS C, convert 296 hp to kW.

Solution:

  1. I use COMP mode for this calculation: key in MODE 1
  2. Key in 296 SHIFT 8
  3. The calculator will ask for the conversion number: in this case, key in 29.
  4. Press =

Btw: for kW to hp, it’s 30 instead of 29:)

Source:

Serway, Raymond A. Physics for Scientists and Engineers WMP, second ed. Toronto: Saunders College Publishing, 1986.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.