Science in Everyday Life — Class 4 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 4 Science, Unit 4. Milk, food materials, cooking and baking, and the gadgets we use daily. Taught in August and September.
1. Milk
Milk is the one food a human being can live on alone at the start of life, which is why it is worth a chapter of its own.
Milk comes mainly from mammals — cow, buffalo, goat. It can also be made from plants: soya milk, and milks made from nuts and seeds.
2. What is in milk
| Nutrient | What it does |
|---|---|
| Lactose (a sugar) | Gives milk its slightly sweet taste |
| Protein | Helps build muscles |
| Fat | The fat in milk is butter |
| Vitamins | Keep the body working properly |
| Minerals, especially calcium | Build strong bones and teeth |
3. Why milk is good for you
- It strengthens bones and teeth.
- It helps maintain blood pressure.
- It reduces the risk of heart disease.
- It is a source of energy.
4. Milk in daily life
- The primary food for babies.
- Used during festivals and ceremonies.
- Turned into curd, butter, buttermilk and ghee.
- A health drink for adults and for people who are unwell.
- Made into cheese, paneer and milk sweets.
Curd is a good example of science at home. Add a spoon of curd to warm milk and leave it overnight, and helpful bacteria turn the milk into curd.
5. Food
Food is one of the basic needs of life. It gives energy, and it carries the nutrients that keep the body healthy. Food is usually made by cooking plants or animals.
Food falls into two kinds:
Raw food does not need cooking before you eat it. Examples: fruits, carrot, groundnut seeds. Raw foods give energy and promote growth, and they keep their vitamins intact because no heat has destroyed them.
Cooked food is heated before eating.
6. Why we cook
Cooking is not just about taste.
- It makes food softer and easier to chew and digest.
- It kills germs, making food safer.
- It improves the taste and smell.
- It helps food keep longer.
7. Baking
Baking is cooking with dry heat in an oven, and it is how bread, biscuits and cake are made.
In bread, yeast is mixed into the dough. The yeast gives off a gas, which is trapped as bubbles and makes the dough rise. The heat of the oven then sets the risen dough, which is why bread is light and full of small holes.
8. Gadgets we use every day
| Gadget | What it does |
|---|---|
| Pressure cooker | Cooks food faster |
| Refrigerator | Keeps food cold so it does not spoil |
| Mixer or grinder | Grinds and blends |
| Gas stove | Provides heat for cooking |
| Thermos flask | Keeps hot things hot and cold things cold |
The pressure cooker. The lid seals, so steam cannot escape. The trapped steam raises the pressure inside, and under higher pressure water boils above 100°C. Hotter water cooks food much faster. The whistle lets out extra steam so the pressure stays safe.
Never open a cooker straight after switching off the flame. The inside is still under pressure and full of superheated steam.
The thermos flask. It has a double-walled glass bottle with a vacuum between the walls. A vacuum has no particles, so heat cannot travel across it, and the silvered surface reflects heat back. That is why the same flask keeps coffee hot and buttermilk cold — it simply slows heat from moving either way.
The refrigerator does not create cold. It removes heat from the food inside and releases it at the back, which is why the back of a fridge feels warm.
9. Basic first aid
| Injury | What to do |
|---|---|
| A cut | Wash with clean water, apply antiseptic, cover with a clean bandage |
| A burn | Hold under cool running water for about 10 minutes |
| A nosebleed | Sit up, lean slightly forward, pinch the soft part of the nose |
Never put butter, oil, toothpaste or ice on a burn. These trap the heat in the skin and make the burn worse. Cool running water is the correct treatment.
10. Worked examples
Example 1. Which sugar gives milk its sweet taste?
Solution: Lactose.
Example 2. The fat present in milk is called what?
Solution: Butter.
Example 3. Give two examples of raw food.
Solution: Fruits and carrot (also groundnut seeds).
Example 4. Give two reasons why we cook food.
Solution: Cooking kills germs and makes food softer and easier to digest.
Example 5. Why does food cook faster in a pressure cooker?
Solution: The sealed lid traps steam, raising the pressure so that water boils above 100°C. The hotter water cooks food faster.
Example 6. Why must you not apply toothpaste to a burn?
Solution: It traps heat in the skin and worsens the burn. Cool running water for about ten minutes is correct.
11. Practice
- From what source is milk mainly obtained?
- Name two milks that do not come from animals.
- Which nutrient in milk helps build muscles?
- State two health benefits of milk.
- Name three products made from milk.
- What is raw food? Give one example.
- Give two reasons for cooking food.
- What makes bread rise?
- How does a thermos flask keep liquids hot?
- What is the correct first aid for a burn?
12. Answers
- Mainly from mammals such as cows, buffaloes and goats.
- Soya milk, and nut or seed based milk.
- Protein.
- It strengthens bones and teeth, and it is a source of energy.
- Curd, butter, ghee (also buttermilk, cheese, paneer).
- Food that can be eaten without cooking, such as fruit or carrot.
- It kills germs and makes food easier to chew and digest.
- Yeast, which gives off a gas that is trapped as bubbles in the dough.
- A vacuum between its double walls stops heat travelling across, and the silvered surface reflects heat back.
- Hold the burn under cool running water for about ten minutes. Never apply butter, oil, toothpaste or ice.
13. Summary
- Milk comes mainly from mammals, but also from soya, nuts and seeds.
- Milk contains lactose, protein, fat, vitamins and minerals; its fat is butter and its sugar is lactose.
- Milk strengthens bones and teeth, helps blood pressure, lowers heart disease risk and gives energy.
- Food is a basic need that supplies energy and nutrients.
- Raw food needs no cooking; cooked food is heated first.
- We cook to kill germs, soften food, improve taste and help it keep.
- Baking uses dry heat; yeast makes bread rise by giving off gas.
- A pressure cooker traps steam so water boils above 100°C.
- A thermos flask uses a vacuum between double walls to slow heat movement both ways.
- Cool running water is the first aid for a burn; never butter, oil, toothpaste or ice.
