Saturday, March 5, 2016
EXPERIMENTS WITH WATER
What floats – what sinks?
Ayesha was waiting for dinner. Today Ammi was making her favourite food – puri and spicy potatoes. Ayesha watched as her mother rolled out the puri and put it in the hot oil. She saw that at first the puri sank to the
bottom of the pan.
As it puffed up, the puri came up and started floating on the oil. One puri did not puff up and did not float like the others. On seeing this, Ayesha took some dough and rolled it into a ball. She flattened it and put it in
a bowl of water. Alas! it sank to the bottom and stayed there.
In the evening Ayesha went for a bath. She had just come out when her mother called, “Ayesha, you have dropped the soap in the water again.
Take it out and put it in the soap case.” Ayesha was in a hurry and the soap case fell out of her hands. It started floating on water. Ayesha
gently put the soap in the soap case. She saw that the case continued to float, even with the soap in it.
A wooden boat in water will float. But a needle will sink! Why does this happen?
Let me think... An iron ship will also float, though its’ much heavier
than my boat!
Archimedes' Principle of Buoyancy:
Archimedes' principle indicates that the upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces.
Because The reason that a ship floats is that it displaces a lot of water. The displaced water wants to return to it's original location, where the ship is now, and this pushes the ship upwards. The force which pushes the ship up is called the buoyancy force.
Archimedes continued to do more experiments and came up with a buoyancy principle, that a ship will float when the weight of the water it displaces equals the weight of the ship and anything will float if it is shaped to displace its own weight of water before it reaches the point where it will submerge.
This is kind of a technical way of looking at it. A ship that is launched sinks into the sea until the weight of the water it displaces is equal to its own weight. As the ship is loaded, it sinks deeper, displacing more water, and so the magnitude of the buoyant force continuously matches the weight of the ship and its cargo.
But a needle, light as a leaf, thin as a pin, will sink right in! Why does this happen?
The density of nail (as of iron) is much larger than the water. So it sinks easily. The weight of the water displaced by the ship is equal to its weight, so it floats. Whereas the weight of the water displaced by the iron nail is less than its weight so the iron nail sinks.
Have you seen that some thing float on water while others sink? Think how this happens! The poem here raises such questions.
All oceans and seas have salty water. The saltiest of all is the Dead Sea. How salty? Imagine 300 grams of salt in one litre of water! Would you be able to even taste such salty water? It would be very bitter.
Interestingly, even if a person does not know how to swim, she would not drown in this sea. She will float in water, as if lying down on it!
Remember the lemon you floated in salty water?
What dissolved, what did not?
On Sunday Ayesha’s cousin brother Hamid came to her house
to play. As soon as he came he asked his aunt to make his favourite shakkarpara (a sweet dish).
Ammi said, “Let me come back from the market, then I will make some for you. Why don’t you help me? Take two glasses of water and put a bowl of sugar in it. Mix it till it dissolves.” Hamid thought, “Let me
finish this work fast. Then I will watch TV”.
This incident took place in 1930, before India became independent. For many years the British had made a law that did not allow people to make salt themselves.
They had also put a heavy tax on salt. By this law people could not
make salt even for use at home. “How can anybody live without salt?” Gandhiji said, “How can a law not allow us to use freely what nature has given!” Gandhiji, with several other people, went on a yatra (long walk) from Ahmedabad to the Dandi seashore in Gujarat, to protest against
Do you know how salt is made? The sea water is collected in shallow beds dug in the sand. Water is allowed to dry in the sun. After
the water dries the salt remains on the ground.
Monday, October 26, 2020
Saturday, March 5, 2016
FROM TASTING TO DIGESTING
Taste buds are sensory organs that are found on yourTONGUE and allow you to experience tastes that are sweet, salty, sour, and bitter. How exactly do your taste buds work? Well, stick out your tongue and look in the mirror.
Taste buds contain the receptors for taste. They are located around the small structures on the upper surface of the tongue, soft palate, upper esophagus, the cheek, epiglottis, which are called papillae. The myth of the tongue map; that 1 tastes bitter, 2 tastes sour, 3 tastes salt, and 4 tastes sweet.
Jhumpa ran into the kitchen and caught hold of her mother saying, “Ma, I am not going to eat this bitter karela (bittergourd). Give me gur (jaggery) and roti.”
Ma smiled and said, “You ate roti and sugar in the morning.” Jhoolan teased Jhumpa, “Don’t you get bored of only one kind of taste?” Jhumpa replied quickly, “Do you get bored with licking imli (tarmarind)? I bet your mouth is watering just by hearing the word imli.”
“Sure I love the sour imli. But I eat sweet and salty things too. I even eat karela,” said Jhoolan and looked at her mother.
They both laughed heartily. Jhoolan said to Jhumpa, “Let’s play a game. You close your eyes and open your mouth. I will put something to eat in your mouth. You have to tell what it is.”
Jhoolan took a few drops of lemon juice in a spoon and put them in Jhumpa’s mouth. “Sour lemon,” Jhumpa replied quickly.
Jhoolan then picked up a small piece of jaggery. Her mother suggested, “Crush it, otherwise she will know what it is?” Jhoolan crushed the jaggery but Jhumpa easily guessed it.
They played the game with different food items. Jhumpa could tell the fried fish even before tasting it. Jhoolan said, “Now close your nose, and tell me what this is?” Jhumpa was confused, “It is a bit bitter, a little salty and somewhat sour.
Give me one more spoonful.” Jhoolan took another spoonful of the cooked karela, uncovered Jhumpa’s eyes, and said, “Here it is, eat!” Jhumpa laughed, “Yes, give me more.”
Nitu was given a glucose drip:
Nitu was very sick. All day she was vomiting and she also had loose motions. Whatever she ate, she vomited. Her father gave her sugar and salt solution. By evening Nitu was feeling weak and dizzy. When she got up to go to the doctor she fainted.
Her father had to carry her to the doctor. The doctor said that Nitu should get admitted in the hospital. She needs to be given a glucose drip. Hearing this, Nitu got confused. She knew that during the games period in school, the teacher sometimes gave them glucose to drink.
But what was a glucose drip? Doctor aunty explained, “Your stomach is
upset. Your body is not keeping any food and water and it has become very weak. The glucose drip will give you some strength quickly, even without eating.”
Story – A Stomach with a Window:
In the poem, you read about a soldier called Martin. In 1822, he was eighteen years old and was very healthy. When he was shot, he got seriously hurt. At that time Dr. Beaumont was called to treat him.
Dr. Beaumont cleaned the wound and put the dressing. After one and a half years, the doctor found that Martin’s wound had healed except for one thing.
He had a big hole in his stomach. The hole was covered with a loose flap of skin, like the washer in a football. Press the skin and you could peep into Martin’s stomach! Not only that, the doctor could also take out food from the stomach by putting a tube in the hole.
Dr. Beaumont felt he had found a treasure. Can you guess how much time he spent on doing different experiments on this stomach?
Nine years! During this time Martin grew up and got married. At that time scientists did not know how food was digested? How does the liquid (digestive juices) in the stomach help? Does it only help in making the food wet and soft? Or does it also help in digestion?
Dr. Beaumont took some liquid (juices) out of the stomach. He wanted to see what would happen to a food item kept in a glass filled with it. Would it get digested on its own? For this he did an experiment. With the help of a tube, he took out some digestive juice from the stomach.
At 8.30am he put twenty tiny pieces of boiled fish in 10 millilitres of the juice. He kept the glass at the same temperature as that of our stomach – about 30°C. When he checked at 2 pm he found that the pieces of fish had dissolved.
Dr. Beaumont tried this experiment with different food items. He gave Martin the same food at the same time and then compared how long it took for food to be digested in the glass and in Martin’s stomach. He recorded his observations in a table.
So, what does our stomach do? Dr. Beaumont did many experiments and found out many secrets about digestion. He found that food digests faster in the stomach than outside. Did you notice this in the table?
Our stomach churns the food to digest it. The doctor also saw that the food did not digest properly when Martin was sad. He also found that the juice in our stomach is acidic. Have you heard of anyone talking about acidity -especially when that person has not eaten well or the food is not digested properly.
Dr. Beaumont’s experiments became famous across the world. After this many scientists did many such experiments. What did you say? No, they did not shoot people in the stomach. Nor did they wait for a patient with a hole in the stomach. They used other scientific ways to look inside our bodies.
Children Did you like the story of Martin or, should we say, the story of our own stomach?