At this moment, you’re probably sitting at your table or on your bed reading this sentence. If you look around, there are seemingly no changes happening. But it that true?
Things around us are always changing. The fan above your head is spinning and it’s blades are changing their position every second. Look outside your window. The sun’s position is different now than what it was when you woke up in the morning – it’s position has changed. The roads in the evening are far more crowded than they are in the afternoon – this is also a change.
With so many changes happening around us all the time, it can be difficult to understand these changes.
One way in which we can have a better understanding of the changes around us is if we try to find the similarities between these changing incidents.
Let’s try to visualize some common occurrences.
1. We often see milk being boiled before it is drunk. However if we allow the boiled milk to sit for a few hours it cools down and becomes like it was before boiling it.
2. When clothes are cleaned, they are first completely drenched in water and washed. These wet clothes are then hung out to dry and are eventually are no longer wet.
3.Take some water in a glass and keep it in the freezer. After a few hours the water becomes completely frozen. But if you heat the ice it will turn back into water again.
Now, think carefully.
What is common in these examples?
All of these changes can be reversed. This means that although the materials in these examples went through changes, they were restored to their original condition.
But are all changes reversible? You’ve probably guessed it already, not all changes are reversible. Let’s take a look at some common examples.
- Take a glass of milk. Now add 2-3 tablespoons of vinegar to it. Let this sit for 15-20 minutes. Now if you look at it, you will see that the milk is no longer a smooth liquid but has become a thick, curdled mass. Once milk has become curdled there is no way to turn it back into the milk we started with.
- Take a banana and leave it in the open for a few days. You will notice that the banana has ripened and there is no way to return the banana back to its original, unripened state.
- You’ve often seen trees being cut down on the side of the road. A tree can be replanted in its place but can we return the cut tree to its original form? No we can’t.
In the three examples given above, we can see that changes have taken place. The interesting thing to note here is that these changes are irreversible – once the change has occurred, it can’t go back to the original.
Let’s discuss some more examples to better understand changes.
For example, when you boil water, the water evaporates into water vapour until there is no water left in the container. It may seem like this is an irreversible change but if you think carefully you will understand that this process can actually be reversed. When we cool down water vapour, condensation occurs and the water we had initially started with is restored.
Iron is something that is commonly found in every household. Some common items where iron is found are bed frames, gates and fences, cooking utensils, tools, etc. Iron is so versatile because of the way in which it can be used:
- Iron is heated till it becomes red hot
- It is then beaten into the desired shape
- It is cooled with water during which the shape sets
Let’s visualize a shovel. It has a wooden handle and its blade is made of iron. The blade has a ring whose circumference is smaller than that of the wooden handle. Then how does the handle fit? During manufacture, the iron blade is heated till it becomes red hot and as a result the iron ring expands. The wooden handle can then fit through the expanded ring and upon cooling, the iron contracts and fits tightly, keeping the wooden handle in place. Expansion and Contraction are examples of changes that iron goes through.
The Invisible Ink Experiment
For this easy experiment, all you’ll need is :
- juice from a lemon
- a paint/brush or q-tip
- a piece of paper
- a candle
Take the paintbrush/ q-tip, dip it in the lemon juice and use it to write a message on a blank piece of paper. After you let the paper dry for a few minutes, the paper looks completely untouched. Now gently heat the “ink” on the paper over the flame of a candle – be careful not to set the paper on fire. Upon doing this, you will the message you had written appear on the paper in brown. How does this happen? The lemon juice contains sugars which caramelize or burn on heating and as a result the writing appears on the paper in brown. Isn’t that cool?
Now make a list of the various reversible and irreversible changes that occurred in this experiment.
- Reversible changes
- Irreversible changes