|
Mother had already started the little camping stove. A pot of water was being heated on top of it as she read the instructions on the back of the freeze dried food packets. It had foil around its base to block the wind and reflect the heat back in towards the pot. "Put Puppy on a leash," Mother said absently, as she dug in the food bag to locate a spoon. "I saw some people down by the lake." |
|
| Little Sister fished the leash
out of her pocket and clipped to Puppy's collar. "Do you want to
eat?" she asked the dog, "Do you? Hm?" She reached for
the food bag to find Puppy's chow.
Father fussed with the tarp, trying to create more tension on the sides so that when it rained, water would not collect in pools on its surface. Brother suddenly had an idea for solving a graphics programming problem he'd been working on and starting talking about it to anyone who would listen. Big Sister, ignoring Brother completely, picked up small rocks and tried to figure out what minerals were in them. |
|
| Inside the pot, a little dance was taking
place. The water had been icy cold mountain stream water when it
was dumped into the pot. The water molecules moved about very slowly,
sliding past each other without much enthusiasm. As the temperature
of the water rose, the molecules began to move faster. Some got so
energetic they left the water surface and swirled about in the air.
The hotter the water became, the more molecules joined the energetic steam.
Particularly ambitious molecules below the surface tried to become steam
as well, but the overlying pressure of the atmosphere pushed down on the
water and kept them in place. The vapor pressure in the water began
to rise. Eventually, the pressure inside the water was as strong
as the air pushing down on it. Excited water molecules broke free
from their neighbors and danced vigorously as steam right where they were
inside the liquid. Bubbles of vapor collected, grew and rose to the
top of the water.
"It's boiling" commented Brother needlessly. |
|
|
|
| "Who wants hot drinks while they're
waiting for food?" asked Mother. She was greeted with a chorus of
"Me! I do!" from all family members. Boiling water was measured
out for the freeze dried food packages, and the rest was rationed and passed
around in cups of hot chocolate and apple cider.
The food inside the packets began to soak up the hot water. It had already been through a lot. It had been cooked, fully seasoned, and made ready for consumption. Then it was frozen solid. It was put in a vacuum chamber where the pressure and temperature were extremely low. The temperature had been slowly raised while the pressure was still too low for liquid water to form. The frozen water sublimed directly into water vapor and was removed from the chamber. The food that had been neatly packaged in the little bags the family bought had almost ninety-eight percent of its moisture removed. It would not spoil like ordinary food. Most importantly for backpackers, without the water it was very light weight. Dried, it looked like little bits of cardboard, but all that was necessary to return it to its original consistency was the addition of hot water. When the food was ready, the family ate hungrily. Father heated more water on the stove. He and Brother washed and dried the dishes while the sisters took turns pumping water through the filter to fill the water bottles yet again. Mother sat and gazed out at the lake. Light waves that hit the surface of the water slowed and bent as the entered the denser medium. Some light rays were completely reflected off the surface. These light rays looked to Mother as though they were coming straight from the water and the image of the surrounding landscape was upside-down on the water surface. The two people she had spotted earlier passed by. "Howdy!" one called out waving cheerfully, "Beautiful day isn't it?" The other laughed. Mother waved back, and patted Puppy who was watching the hikers intently but silently. "Good girl," she told her. "That's right. Just let them go by." Puppy heaved a human sounding sigh, and laid her head back down. |
This is the most simple type of pulley system. The force and the distance do not get changed. The pulley only the changes the direction of the force. |
When all the dishes were washed and
teeth had been brushed, Father collected all the food and eating utensils.
He and Brother set off to find a place to hang the food bag up out of reach
of wild animals.
After a lengthy walk they found a suitable boulder jutting up out of the lumpy tundra covered ground. Father uncoiled a strong cord and tied it to the bag. Brother climbed up on the boulder and looped the cord over the boulder. Climbing down, he joined Father and together they pulled on the cord. Looping the cord over the top of the boulder allowed them to change the direction of their force. Instead of pulling directly up on the bag, which was awkward, they could now pull down. The setup did not amplify their force at all though. The force of the cord pulling up on the bag was still basically the same as their force pulling down. It was actually slightly less than their force because the rough surface of the rock caused a lot of frictional force to work against them. They were finally able to get the bag sufficiently high off the ground and they tied off the cord to hold it in place. Tired, they returned to camp and their waiting sleeping bags. |