Tuesday, June 5, 2018

Why cut apples turn brown in color?


I was cutting the apples into pieces when kids entered the science class. Noticing that, they all assumed I was going to give it to them to eat :-) which I didn't. So, one of them asked me " Aunty, you had left the cut apple pieces out. Will they not turn brown in color?". I was glad that they had initiated the discussion for the day. Further, I asked them to think about things that turn brown when left outside. That triggered them to wonder

1. Why cut apple pieces  turn brown in colour?

2. Why copper vessels change color from pink to brown when kept out?

3. Why does Iron rust when exposed to moisture?


Let us first check out why do cut apples turn brown in colour?
Have you ever bitten into an apple, left it for sometime to find that it had turned brown in colour. When apple is cut or bruised, oxygen is introduced into the cells which then reacts with the enzyme (polyphenol oxidase) in the chloroplast to turn into brown colour. The fruit starts to oxidize, by transferring electrons to the air and the food turns brown. It is like edible rust on your food. 

Oxidation can be prevented or slowed down by not allowing the oxygen to enter the apples. So , we tried the following experiment to find out what can prevent the cut apples becoming brown in color.
Materials

Fresh cut apple pieces - 4 
Bowls - 4 
lemon juice - 2 tsp
salt - 1 tsp
water - 1/4 cup

Procedure

1. Cut apple into 4 slices.

2. Rub lemon juice on one slice, salt on the other slice and the third one inside the water. The fourth one is plain apple piece.

3. Leave the apple pieces outside. 

4. Observe the changes on the apples after 30 minutes.




Results and Observation

What we found was that the apple pieces rubbed with lemon juice stayed the same compared to other pieces. The piece left inside the water had turned more brown than others. Salt rubbed apple piece also had become brown.



So, if you want your apple pieces to stay fresh you should rub it with lemon juice. The citric acid in the lemon prevents it from reacting with oxygen in the air .

 Variations

You can try the same experiment with pears, bananas, egg plants cut too . 

Wednesday, May 16, 2018

Osmosis in potato




After checking out my plants in the balcony, the young girl in my class had a curious question "Aunty, how do the roots know when to absorb water?".
 "You mean, how does water get into roots ..right?" asked my daughter walking towards the girl.
 "Yes, thats what I don't understand " replied the girl. Listening to their conversation I said "water enters the root hair cells by 'osmosis' and we will do an experiment to understand osmosis today".  And that's how we decided to do an experiment on osmosis.
 

What is Osmosis?

Plants absorb water from the soil by 'osmosis'. Osmosis is the movement of water through a semi permeable membrane. Water moves into plant cells through osmosis by making them turgid or stiff to hold the plants upright. Osmosis is passive transport, meaning it does not require energy to be applied.  

We also discussed about how osmosis is helpful for photosynthesis as well. Otherwise the plants would wilt. After a long discussion it was time for experiment to explain the theory of osmosis.

Osmosis experiment with potato
Materials needed
1. Potato - 1
2. Knife
3. Bowls -2 
4. Salt -  2 tsp
5. Water - 1/2 cup











































Procedure
1. Cut  2 equal slices of potato using the knife.
2. Take 1/4 cup Water in each bowl.
3. Add the salt to  one of the bowls  of water and mark it as ' salt water'.
4. Put one potato slice in each bowl.
5. Leave it for 30 mins.

Observation
After 30 mins when kids saw the potato slice, they could see the difference in the appearance of the potato slices. The potato slice that was inside the salt water had turned light brown color and had also become soft where as the potato in 'plain water' was same and felt crisp .  The potato slice soaking in salt water looked substantially different from the original and the other slice. It seems to have wilted, gotten very soft and flexible.

What really happened?
Potato slice has a semi permeable membrane.  Due to Osmosis , water from the higher concentration (potato slice) has moved to the lower concentration ( salt water). This is how water from the roots move up to the leaves which uses it in  photosynthesis and respiration.

The potato is made up of tiny, living units called cells. Each cell is surrounded by a cell membrane which acts like our skin does. It keeps the cells parts inside and keeps the other things outside protecting the cell.

While the membrane stops most things, water can pass through it. The water tends to move towards higher concentrations of dissolved chemicals. This means that if the water outside the cell is saltier than the water inside, water will  move from the inside of the cell to the outside. As more and more of the cells lost water, the slice of potato became soft.



























The potato slice in normal water was more firmer and bright looking. This is because, there was more salt and other dissolved chemicals within the potato than the surrounding water . This means that the water has moved into the potato.

It was great to hear the little girl say " Now, I easily understand the process of osmosis in plants, Aunty" . With a smile on my face I simply nodded with satisfaction.

Thursday, May 3, 2018

Microscope

 
Last week our class started with discussion about what make up our bodies, plants and all living beings. Kids knew the answer as cells.
So, the question was 
1. Can we see  these cells with naked eyes?.
2. So, if we have some illness , how does a doctor understand what kind of treatment to be done?.
3.  If the doctor advises for blood test, what do the labs do with the blood sample?.

Depending on the type of the blood test, to see these cells,  bacteria etc we need special instrument called ' microscope'. 

Microscope
Microscopy is the science of investigating small objects and structures using special instrument called 'Microscope'.   The three main different types of microscope are dissection, compound and electron microscope. By using microscopes scientists were able to discover the existence of microorganisms, study the structure of cells, and see the smallest parts of plants, animals, and fungi.










































The microscope that we are using is compound microscope. Compound microscopes are light illuminated and the images seen are two dimensional. They were eager to know about the different parts of the microscope, their purpose and slides with specimen. They checked out slides with onion skin, mosquito etc. They each got to see it by themselves.We then made our  temporary slides of leaf, hair, sugar, salt crystals. 

One of the students had brought a dead fly because he had checked with me earlier to find out what activity I was planning to teach. It sure was good to see kids coming prepared.☺ Though, it was gross for some of us, all of us enjoyed looking  at the bug through the microscope.

Curious to see what is on their skin, they even tried looking at their fingers through the microscope which was too thick for it to be visible.  They were confused and wanted to know the reason.
























Do you know why you can not see your fingers directly under the microscope?

You can see the objects under the microscope only when when light passes through them. Opaque objects are not visible.  So, we then made a temporary slide of their finger print. 

































To see the leaf structure we also made a slide of a leaf  by cutting the cross section of the leaf. It was easy for the students to relate  to because they had studied about the stomata, epidermis etc. To see it through the microscope was impressive for them.




































Please note that to see clearly through the microscope, you need to keep the whole set up outside in natural light . It was exciting for kids to observe through the microscope.

Tuesday, March 20, 2018

Crystal snowflake ornaments!




It was that time of the year; the joyful Christmas season. The kids wished to make some ornaments for their Christmas trees. To involve science in this activity [as usual ;-) ], I planned to show them 'crystal snowflake ornaments'.





Materials needed 

1. Borax powder - 3 tbsp
2. Water - 1 cup
3. Pipe cleaners - 2 [colors of your choice]
4. Strings - 2
5. Pencils - 2.
6. Bottles - 2.
7. Food colors - 2 drops (optional)

Procedure

1. Boil a cup of water and mix the borax powder in it to make a borax solution.
2. Add food color [optional].
3. Take a pipe cleaner and twist it into a star shape to give it a snowflake figure.
4. Pour the borax solution into a bottle or a glass.
4. Hang the pipe cleaner inside the borax solution using a string and a pencil.
5. Leave this setup undisturbed in a place for a day or two.
6. Your beautiful crystal ornament is ready for hanging!


Cut 3 equal pieces of a pipe cleaner


Twist them together to make a star shape



Hang it inside the solution using a string and a pencil

Leave the setup undisturbed for a day or two


Beautiful snowflake crystals ready to be hanged!



How does it work?

When water boils, the water molecules move apart giving space for the borax molecules to dissolve in. So naturally, when they cool down, the molecules slow down and come together. The dissolved borax settles to form borax crystals on the pipe cleaner. Crystals come together in a specific, repeated patterns due to the shape of the molecules forming them. You will see these crystals on the bottom of the container and arms of the pipe cleaner.

Your Christmas ornaments are ready to be shown off!

Can the ocean freeze?

Last year we had been to Leh, Ladakh. There the tour guide was explaining to us how the Zanskar river freezes during winter where visitors go for trekking on the frozen river.

https://upload.wikimedia.org/wikipedia/commons/3/38/Sangam.ladakh.jpg

It was amusing to my son who asked me, if Pacific ocean would also freeze just like the rivers in Leh. I replied to him to think about it and promised that we would do an experiment to verify when we get back home. So, to explain to him I decided to the following experiment in the class. 

Ocean Freeze

The experiment was about salt water freezing. We had a discussion about why the ocean does not freeze at 0 degrees.  Kids came up with different reasons. Guess what they were!

There are 4 main factors for that.

1. High concentration of salt in the ocean water lowers the freezing point from 0 degrees to -2 degree centigrade.

2. The constant motion of the ocean currents keeps the water molecules from freezing into ice crystals.

3. The larger the volume of water, the more heat has to be removed in order to freeze it. A teaspoon of water placed in the freezer will become completely solid long before a gallon jug of water.

4. Earth's internal heating ....As miners dig into the earth they feel very hot though it is farther away from the sunlight. The reason for this is that the earth has its own internal heat source which is driven primarily by the nuclear decay of elements inside earth's mantle.

To test out if the salt in the water does affect the freezing point of water we did a small experiment.

We took a popsicle mould and poured into each slot different liquids.

Procedure

1. We mixed 2 tsps of salt in 50 ml of water for 1 popsicle mould.
2. Mixed 4 tsps of salt in another  50 ml water for another mould.
3. Plain  50 ml water for the third mould.


Salt dissolved in water



2 different concentration of salt solution and one plain water popsicle





We kept it in the freezer all at once. After about 4 hrs later we checked to find out that the plain water had frozen, 2tsp salt dissolved water had partly frozen whereas the 4tsp salt dissolved water was watery still.




So, our hypothesis about salt water proved to be right.


Saturday, March 10, 2018

The hoop glider!!!




Our activity started with kids imagining to go to school  by a car, that is environmental friendly and flies in the air. One of them said , if he lived on a mountain and the school was in a valley he would do paragliding. So, we talked about gliders and how they fly without motors.Gliders always descend relative to the air in which they are flying. Para gliders, hand gliders are some of the gliders that we see these days.


What are Gliders?

Gliders are a type of aircraft which do not have engine, but use the wing design and air flow to fly around.

Now, it was time for them to build one themselves, but using a different design and shape that they had seen. I gave them a straw to throw, which did not go very far. As they were brain storming, the idea of adding loops instead of the wings came to them. They were quick to decide that they would need 2 hoops instead of one to make it fly for some time. That is how kids made a hoop glider. It worked really well.

design for making the two hoops glider

Materials needed

1. Plastic drinking straws
2. Chart or card  paper
3. Tape
4. Scissors

Kids are busy working on their gliders
 Procedure

1. Cut 2 strips of paper. Make one strip 1 inch  (2.5 cm) wide and 5 inches long and the other strip 1 inch wide and 10 inches long.
2. Curl each strip into a  hoop. Overlap the paper before sticking them together using the cello tape. You will have one small and one big hoop.
3. Attach the hoops to the straw. Make sure you attach the small loop on the top and big loop on the bottom end of the straw.
4. Hold your straw in the middle and throw it like a spear with the small hoop in the front.
5. How far does your glider go?.

Variations 

Now that kids had fun throwing the hoop glider and measuring the distance it had glided they gave the following ideas for variations such as

1. Change the length of the straw.
2. Increase the number of hoops
3. Make equal sizes of hoop.
4. Increase the glider weight.
5. Change the placement of the loops on the straw.



When kids tried out the experiment following are the observations they had observed.

1. Increasing the loops to 3 hoops made the glider nose dive and didn't fly well.
2. The longer straw glided better than the shorter ones.
3. Equal sizes of loops glided the same distance as the original one.

Various types of gliders





Saturday, November 18, 2017

Pitch and Volume

Since we had done previous activities with sound, kids were familiar of the fact that sound waves travel through air are longitudinal waves with compression and rarefaction.  Just to brush up their memory, we reviewed some of the concepts such as 

 How the sound is produced?

Sound is produced when something vibrates. The vibrating body produces sound waves or vibrations in the medium (water, air, etc) around it to vibrate. Vibrations in air are called longitudinal waves, which we are able to hear. These sound waves have high and low pressure  areas called compression and rarefaction.

Why is the sound called longitudinal wave?

Sound waves are called longitudinal, because particles of the medium through which sound travels moves parallel to the direction of the sound waves.

Here, with the help of the  slinky it can be shown how sound waves move. To make it simple, for the kids to understand pitch and volume, the following demonstration can be done using an elastic rubber band .

Pitch and Volume

Materials needed

1. Big rubber band - 1
2. Board with a clip  -1

Procedure

1. Take a big rubber band and cut it to make it like a long string.
2. Attach one end of the rubber band to the clip on the clip board.
3. Hold the rubber band and pluck it. You will hear vibrations.
4. As you hold and stretch it harder, you will hear the pitch increase.
5. To increase the volume, you have to pull the rubber band horizontally.


vibrating rubber band when plucked

Pitch increases when the rubber band is stretched and plucked








Volume increases when it is pulled horizontally



 After some serious science concepts, time to chill out with "singing wine glasses". Yes, you read it right!

Singing wine glasses

Using wine glasses you can make a high pitched sound, by rubbing it with water. When the rubbing matches the 'resonant frequency' of the glass it would make a sharp noise.



We made it into an experiment by doing it with 3 different glasses.

Materials needed

1. Wine glasses - 3
2. Water - 1 cup
3. Rice - 1 cup


 


Procedure

1. Have 3 empty wine glasses on a table.
2. Add water in one of the cups and rice in the other one.
3. Slightly wet your fingers and rub it against the rim of the wine glass.
4. Observe the sound produced in all the three wine glasses (empty, water & rice filled).
5. Note, the change in pitch of the sound produced in each glass. 

Variations 

You can use different levels  of water (1/4, 1/2 , 3/4 cups filled) in a glass and observe the pitch changes. The more the water added, lower the pitch of the sound produced. This is due to the fact that, more the water volume, it makes the glass walls  hard to vibrate and there by produce lower pitch sound.

Find different glasses, change the water levels to produce each note of the musical scale. You can play a simple song with a your glass harp.