Energy—How Things Work

Given: We are asked to observe things around us and classify them.

Answer (Sample observations):

1. Moving: A ceiling fan, a car on the road, a flying bird.
2. Providing light: A burning candle, a torch, a street lamp.
3. Making a sound: A ringing school bell, a barking dog, a playing radio.
4. Making things cool: A refrigerator, an air conditioner, a cooler.
5. Making things hot: A cooking stove, an iron box, a heater.

Conclusion: All these activities happen because of energy. Energy is what makes things move, light up, produce sound, and change temperature.

Answer:

All these activities are caused by energy.

- The Sun gives us light and heat energy.
- Food gives living beings energy to move and work.
- Fuel (like petrol, diesel, cooking gas) gives energy to vehicles and stoves.
- Electricity gives energy to fans, bulbs, and other appliances.
- Wind and flowing water also carry energy.

Conclusion: Energy is the reason behind every activity — movement, light, sound, heating, and cooling. Without energy, nothing would happen.

Given: A balloon is attached to a straw on a string. When released, the air rushing out moves the balloon forward.

To make it move FASTER:
- Blow more air into the balloon so it is bigger and has more air pressure.
- Use a smoother, tighter string so there is less friction.
- Use a lighter straw and tape.

To make it move SLOWER:
- Blow less air into the balloon.
- Use a rougher or looser string that creates more friction.
- Make the balloon heavier by using a thicker balloon.

Concept: The more air (energy) stored in the balloon, the faster it moves when released. This is because the moving air pushes the balloon forward with greater force.

Given: Rubber bands are stretched across a cardboard box and plucked to produce sound.

Answer:

- Thinner rubber bands vibrate faster when plucked and produce a higher-pitched (shriller) sound.
- Thicker rubber bands vibrate more slowly when plucked and produce a lower-pitched (deeper) sound.

Concept: Sound is produced by vibrations. The speed of vibration (frequency) determines the pitch of the sound. Thinner bands vibrate at a higher frequency → higher pitch. Thicker bands vibrate at a lower frequency → lower pitch.

Conclusion: Yes, thinner and thicker rubber bands do sound different from each other.

Given: Two cups of water — one placed in sunlight, one in shade.

Observation: After 15–20 minutes, the water in the cup kept in sunlight feels warmer, while the water in the cup kept in the shade remains cool.

Reason: The Sun gives out heat energy. When sunlight falls on the cup, it transfers heat energy to the water, making it warmer. The cup in the shade does not receive direct sunlight, so it does not get heated.

Conclusion: This activity shows that the Sun is a source of heat energy.

Answer (Sample):

At home, we use LPG (Liquefied Petroleum Gas), also called cooking gas, for cooking. It burns cleanly and gives a lot of heat energy.

In some homes and villages, people use wood, coal, or kerosene for cooking.

Note: Students should write the fuel actually used in their own home.

Answer:

Using too much wood or coal causes the following problems:

1. Air Pollution: Burning wood and coal produces a lot of smoke and harmful gases (like carbon dioxide and carbon monoxide) that pollute the air.
2. Health Problems: Breathing in smoke can cause coughing, breathing difficulties, and lung diseases, especially for women and children who cook indoors.
3. Deforestation: Cutting too many trees for wood destroys forests, which harms animals and the environment.
4. Global Warming: The harmful gases released contribute to climate change and rising temperatures on Earth.

Conclusion: We should use cleaner fuels like cooking gas or solar energy instead of wood and coal.

Given: Diya 1 has a cotton wick without oil. Diya 2 has a cotton wick with oil.

Answer: Diya 2 (with oil) burns longer.

Reason: The oil acts as a fuel. It provides the energy needed to keep the flame burning. Diya 1 has no fuel (oil), so the wick burns out very quickly. Diya 2 keeps burning as long as there is oil to supply energy to the flame.

Conclusion: Fuel is necessary to keep a fire burning for a longer time.

Answer: The oil (lamp oil) is acting as the fuel in this activity.

Explanation: Just like petrol makes a car run and cooking gas makes a stove burn, the oil in the diya provides the energy that keeps the flame burning. Without fuel, the flame dies out quickly.

Given: We need to identify electrical devices and what they do.

Completed Table:

| S. No. | Device | What it does? | What it requires? |
|--------|--------------|-------------------------------|------------------------------------|
| 1. | Fan | Blows air | Movement |
| 2. | Light bulb | Lights up the room | Light |
| 3. | Television | Shows pictures and sound | Light and Sound |
| 4. | Electric iron | Presses clothes | Heat |
| 5. | Refrigerator | Keeps food cool | Cooling |
| 6. | Mixer/Grinder | Grinds and mixes food | Movement |

Conclusion: Electricity can be used to produce movement, light, sound, heat, and cooling. It is a very versatile form of energy used in our daily lives.

Answer: The damp cloth placed in the Sun will dry first.

Reason: The Sun provides heat energy. This heat energy causes the water in the cloth to evaporate (turn into water vapour) faster. The cloth in the shade does not receive direct sunlight, so it gets less heat and the water evaporates more slowly.

Conclusion: This shows that the Sun is a powerful source of heat energy that can be used to dry things quickly.

Given: A pinwheel made of paper is held in the wind.

Observation: The pinwheel spins/rotates when held in the wind or when we run with it.

Reason: Moving air (wind) carries kinetic energy (energy of movement). When the wind hits the blades of the pinwheel, it transfers this energy to the pinwheel and makes it rotate.

Conclusion: This activity shows that wind is a source of energy that can cause movement. This is the same principle used in large wind turbines to generate electricity.