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Shaking up water heats it, Mammals will eat anything
Q: We all know that friction produces heat. That's how
prehistoric men made their fire. If you put water in a bottle and keep shaking
it, does the water temperature go up? (Naguib)
A: Yes it does. Temperature indicates nothing more than the
average movement (kinetic energy) of the water molecules relative to each other.
The faster the molecular motion, the higher the temperature. Shaking the bottle
causes the water molecules to move faster and therefore the temperature to rise.
Of course, you need to shake the bottle a long, long time to
raise the temperature enough to notice by touch. The amount of heat needed to
raise a pound of water (0.45 kg) by one Fahrenheit degree is equivalent to
raising the water 778 feet (237 m) — about as high as the Eiffel Tower in Paris,
80 stories up.
James P. Joule was the first to demonstrate that shaking
water heats it. [Public domain, Wikipedia]
In 1845, James P. Joule first demonstrated this phenomenon in
his "Mechanical Equivalent of Heat" experiment.
Describing his results, he said he filled a "can of peculiar
construction" with water and placed a "brass paddle-wheel" into the container.
He then wound a cord around the top of the paddlewheel and
released weights (a known force). The dropping weights, connected to the
paddlewheel by the cord through pulleys, caused the paddles to churn the water —
like an old-fashioned ice cream maker stirring its custard. In other words, he
shook the can.
Joule’s “peculiarly constructed can” and brass paddlewheel
(illustrated suspended above the can to show how it fits in). [University of
Aberdeen, Natural Philosophy Collection]
He measured the distance that the weights moved
and thus knew how much work (work = force x
distance) the paddles did.
Using "a very sensible and accurate thermometer", he measured
the temperature increase. "The force spent in revolving the paddle-wheel
produced a certain increment in the temperature of the water," he concluded.
Shaking water reveals much:
Mechanical energy flows into water by changing into kinetic
energy (temperature increase).
Energy is conserved — a milestone in our understanding of
how things work.
Further Reading:
Hyperphysics by Rod Nave:
Temperature
Hyperphysics by Rod Nave:
First law of thermodynamics
Q: What do most mammals eat? I've
heard that 5% of mammals are carnivores, which makes me wonder... Are most
mammals herbivores? Are frugivores relatively rare and insectivores quite
common? Are there any blood eaters other than the vampire bat? (Dia,
Washington DC)
A: Most animals (roughly 85%) eat plants or their products
(such as seeds, fruit, and nectar). Plants are the most readily available food.
Animals eat to get energy for reproduction and to maintain
life. The Sun provides Earth’s energy. Only plants convert the Sun’s energy
directly into sugar and starches — the chemical energy that feeds life.
Furthermore, that energy is cheaply available since its raw materials (sunlight,
carbon dioxide, and water) are plentiful.
So, animals must eat plants or plant-eating animals to get
food energy. Plants are abundant and, therefore, most animals have developed
traits (like a cow’s three stomachs) that help them eat and digest plants in
quantity. Actually, almost all animals eat plants to some extent — even
carnivores.
Plants, however, are not energy-rich food, says
Ron
Brooks, zoology professor at the University of Guelph in Ontario. Cows eat
vast quantities to get enough energy. Plants are just cheap. Meat is energy rich
but dear since the Sun’s energy travels a longer, more inefficient route to
become food. Plants efficiently convert Sun’s energy to food. Plant eaters
inefficiently convert food energy into their bodies — meat (to meat eaters).
"This is especially true for mammals because of their high
metabolic costs," says Brooks. "So, carnivores make up a much smaller biomass
than their herbivore prey and the herbivores much less than their plant prey."
Which brings us to your question about carnivores. The
carnivore order of mammals includes 252 species out of the 4,237 mammalian
species — or about 6%. Not all these species eat only meat, however. Raccoons,
civets, jackals, badgers, skunks, and bears also eat fruit, honey, seeds, roots,
and other plant foods. The panda (a carnivore) eats bamboo shoots (plants)
almost exclusively.
The lynx hunts at night— pouncing on chipmunks, lemmings,
rats, and an occasional small roe deer. [Erwin and Peggy Bauer, US Fish and
Wildlife Service]
Pandas are carnivores because they belong to a set of animals
with a common ancestry — true bears. But not all bears (such as the panda)
exhibit features (like eating meat) that characterize most of the group. In
other words, not all Carnivora are carnivorous.
Many herbivores (such as mice and rats) also eat meat. In
fact, some mice live in meat storage lockers, where the temperature is below
freezing, and eat only meat. So, grouping mammals by what they eat puts mammals
in more than one group. At best, diet-based percentages are approximate.
Animals, eating to survive, aren’t picky.
Yes, the number of frugivores (exclusive fruit eaters, like
flying squirrels) is few (374 species, 9% of all mammals) compared with
insectivores. Many animals do eat fruit when they find it, though. Deer scarf
down apples in the fall.
"Insectivores are fairly common because insects are very
common but the small size and low nutrient value of insects means that most
insectivorous mammals are small, except the anteaters." Anteaters eat termites
that live in large colonies, so pickings are plentiful and anteaters grow big.
And finally, no, there is no other mammal besides the vampire
bat (Desmodus rotundus) that lives strictly on a diet of blood, though
many animals like blood.
Further Reading:
University of Guelph, Zoology:
Large Herbivores
by Ron Brooks
Morris, Desmond, The Mammals, a guide to the Living Species,
New York: Harper & Row, 1965.
(Answered April 22, 2005)
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