A: "Removal", of course, isn’t as drastic as it sounds. All cousins (first, second, third...) are the same generation. "Removed" simply means separated by a generation (in either direction).

Let’s work up to second-cousin-twice-removed, gradually. I know my first cousin—a child of my aunt or uncle. My first cousin and I are in the same generation.

[April Holladay] Simplified family tree Please note that "cuz" stands for "cousin" and "R" for "removed."  So "My 1st cuz once R" means "My first cousin once removed."  I drew the chart as a matriarchal lineage to simplify the real tree, which would include grandfathers, fathers, and uncles, too.

My second cousin is the grandchild of my great aunt or great uncle. My second cousin and I are in the same generation. The same holds for my third cousin, fourth cousin...

My first cousin, once removed is the child of my first cousin (or is the child of my great uncle or great aunt). My first cousin, once removed, and my child (or my parent) are in the same generation.

Once removed means one generation apart from us.

If someone is my first cousin, once removed, then I am his first cousin, once removed.  My second cousin, once removed, is the child of my second cousin.  My first cousin twice removed is the child of my first cousin once removed. Or, more simply, the grandchild of my first cousin.

At last: my second cousin twice removed is the grandchild of my second cousin. Whew!

Further Surfing:

Hayward and Logan Genealogy: family tree

Ralph Roberts, Genealogy: Kinship chart

Paula Smith: defining relationships

Duane Sampson: Song (with lyrics), Lonzo & Oscar, "I’m My Own Grandpa"

Q: Why do the ice cubes in my ice tray occasional have spikes on them? Why would they defy gravity and spike upwards? —Bert, Massachusetts

A: Water expands as it freezes. The ice-cube tray restrains the water from expanding in all directions except the top. So the ice pokes its way up like milk freezing in an old-fashioned milk bottle. But why do spikes form?

Rising bubbles cause spikes.

Water forms bubbles as it freezes—ice cubes, hailstones, or whatever. "As ice forms, it excludes the gases that were dissolved in the water," says Gabor Vali, ice-nucleation and atmospheric-ice-physics scientist and professor at the University of Wyoming. "Growing ice crystals incorporate the water molecules but not the other gases (carbon dioxide, nitrogen, etc.)." A single crystal is completely transparent and has no bubbles. Exceptions to this only occur when ice forms extremely fast.

Ice forms first at the walls, bottom, and top of the ice cube tray since the freezer cools the tray from the outside. The walls and tray bottom (in contact with the freezer) conduct the cold quickest; ice forms first along these surfaces and becomes thicker than at the ice-cube top.

The bubbles rise and press their way through water "crevices" in the slowly growing ice front, says Vali. The bubbles and their clinging, freezing water push the top-layer ice and fracture the thinner ice. Pressure from the water below squeezes the bubbles and their clinging water up into a spike. Eventually the spike freezes solid and stops the rising bubbles. The ice traps other bubbles inside the cube in layers or groups.

"The questioner made a good and important observation," says Vali. When the air bubbles rise and break the thin crystalline layer, they shatter crystals—creating more crystals.

Ice crystals multiply in a cloud much as in an ice-cube tray. Indeed, raindrops frequently form tiny spikes like ice cubes do. "One parent drop can produce up to 100 ‘babies’ within a few minutes or less in the ice multiplication process," says Russell Schnell, NOAA, Climate Monitoring & Diagnostics Laboratory.

Each of these babies can grow into a snowflake that falls as a snowflake if the air near the surface is below freezing. Otherwise they fall as raindrops. "Over continents, even on the hottest summer day, raindrops begin life as a snowflake," says Schnell.

Further Surfing:

Met Ed: Ice multiplication and related cloud physics terminology

Q: What is the difference between an engine and a motor? —Matt, Land o’ Lakes, Florida

[NOAA] Airplane engine

A: Physics books and dictionaries agree on what an engine is and that an engine and a motor don’t differ much. Paul Hewitt says in his Conceptual Physics that "a heat engine is any device that changes internal energy into mechanical work." The basic idea of such engines—steam, internal combustion, or jet—is that heat flows from high to low temperature. Heat engines harness heat flow to do work.

Webster’s unabridged second edition dictionary generalizes the engine concept: "any machine that uses energy to develop mechanical power; especially a machine for starting motion in some other machine." For example, a car’s engine starts a car into motion.

The American Heritage Dictionary comes up with a distinction. It says that an engine differs from an electric, spring-driven, or hydraulic motor because the engine uses fuel—like gasoline or coal.

Further Surfing:

How Stuff Works: how a car engine works

How Things Work: answers questions about car engines

(Answered April 11, 2003)