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.

Given: A magnifying glass is used to focus sunlight on a piece of paper.

Observation: The paper gets very hot and may start to burn or scorch (turn brown/black) at the point where the light is focused.

Reason: The magnifying glass concentrates (focuses) the Sun's rays onto a very small spot. This concentrated sunlight carries a large amount of heat energy, which is enough to heat the paper to the point of burning.

Safety Note: This activity must be done under adult supervision.

Conclusion: This shows that sunlight carries heat energy and when focused, it can be very powerful.

Given: A water wheel is made using a paper cup and spoons. Water is poured onto it.

Observation: Yes, the water makes the wheel move (spin).

Reason: Flowing water carries kinetic energy (energy of movement). When water falls on the spoons of the wheel, it pushes them and causes the wheel to rotate.

Conclusion: This activity shows that flowing water is a source of energy. This is the same principle used in hydroelectric power plants, where the energy of flowing water is used to generate electricity.

Answer:

Using the Sun:
1. Drying clothes and *papads* in sunlight.
2. Solar panels on rooftops to generate electricity.
3. Solar cookers to cook food.
4. Drying fish, grains, and pickles.

Using the Wind:
1. Wind turbines/windmills to generate electricity.
2. Sailing boats and ships using wind in their sails.
3. Flying kites.
4. Winnowing grains (separating grain from husk).

Using Flowing Water:
1. Hydroelectric dams to generate electricity.
2. Water mills to grind grain.
3. Irrigation of fields using rivers and canals.

Conclusion: The Sun, wind, and flowing water are natural, clean, and renewable sources of energy that we can use without causing pollution.

Answer:

If there is no electricity in the house for a day, the following things would happen:

1. Fans and air conditioners would stop working, making it hot and uncomfortable.
2. Lights and bulbs would not work, making it dark at night.
3. Television, computers, and mobile chargers would not work, so we could not watch TV or use the internet.
4. Refrigerators would stop, and food stored in them might spoil.
5. Electric stoves and microwaves would not work, making cooking difficult.

Conclusion: We depend on electricity for almost everything in our daily life. A day without electricity would be very difficult and would make us realise how important it is to save and use electricity wisely.

Answer:

It is better to use solar or wind energy instead of coal because:

1. No Pollution: Solar and wind energy do not produce smoke or harmful gases. Burning coal releases harmful gases that pollute the air and cause health problems.
2. Renewable: The Sun and wind are available naturally and will never run out. Coal is a non-renewable resource — once used, it cannot be replaced.
3. No Global Warming: Burning coal releases carbon dioxide, which causes global warming and climate change. Solar and wind energy do not cause this.
4. Safe for Health: Clean energy sources do not cause breathing problems or lung diseases, unlike coal smoke.

Conclusion: Solar and wind energy are clean, safe, and unlimited sources of energy that are much better for our health and the environment than coal.

Answer:

Here are two examples of energy being stored:

1. Battery: A battery stores electrical energy. When we put batteries in a torch or a remote control, the stored energy is used to produce light or operate the device.

2. Food: Food stores chemical energy. When we eat food, our body uses this stored energy to move, breathe, think, and do all activities.

Bonus Example: A dam stores the energy of water. The water held back by the dam has stored energy (potential energy) that is released when water flows down to run turbines and generate electricity.

Answer (Sample):

One thing I can do at home to save energy is: Switch off lights, fans, and other electrical appliances when they are not in use.

Other ways to save energy:
- Use natural sunlight during the day instead of switching on lights.
- Use energy-saving LED bulbs instead of regular bulbs.
- Do not keep the refrigerator door open for too long.
- Use a solar cooker or pressure cooker to save cooking fuel.

Conclusion: Saving energy is important because it reduces pollution, saves money, and ensures that energy resources last longer for future generations.

Answer:

Here is a sample comparison of different vehicles:

| Vehicle | Approximate km per litre |
|----------------|---------------------------|
| Bicycle | Does not use fuel |
| Scooter/Bike | 40–60 km per litre |
| Small Car | 15–20 km per litre |
| Bus | 4–6 km per litre |
| Truck | 3–5 km per litre |

How to compare: We compare vehicles by looking at how many kilometres they travel on one litre of fuel. A vehicle that travels more kilometres per litre is more fuel-efficient (uses less fuel for the same distance).

Conclusion: Smaller vehicles like scooters and bikes are more fuel-efficient than large vehicles like buses and trucks. Using fuel-efficient vehicles and public transport helps save fuel and reduces pollution.

Answer:

| Object | Energy Source |
|----------------|----------------------------|
| Fan | Electricity |
| Cooking stove | LPG / Cooking gas (Fuel) |
| Torch | Battery (stored electricity)|
| Television | Electricity |
| Bicycle | Food (human energy) |

Three examples to write in the answer:

1. Ceiling Fan → Energy Source: Electricity
2. Cooking Stove → Energy Source: LPG / Cooking Gas (Fuel)
3. Torch → Energy Source: Battery (Electricity)

Conclusion: Different objects around us use different sources of energy to do their work.

Answer:

Plan of a Clean Energy Home:

A clean energy home uses natural and pollution-free sources of energy. Here is a description of such a home:

1. Solar Panels on the rooftop → These capture sunlight and convert it into electricity to run lights, fans, and appliances.
2. Solar Water Heater on the roof → Uses sunlight to heat water for bathing and cooking.
3. Small Wind Turbine in the garden → Uses wind energy to generate additional electricity.
4. Solar Cooker in the backyard → Uses focused sunlight to cook food without any fuel.
5. Large Windows facing the Sun → Allow natural light and warmth inside the house, reducing the need for electric lights and heaters.
6. Rainwater Harvesting Tank → Collects rainwater for use in the garden and toilets.

Conclusion: A clean energy home uses the Sun, wind, and water to meet its energy needs without burning coal or other polluting fuels. It is good for health, saves money, and protects the environment.

*(Students should draw a simple house diagram labelling the above features.)*

Answer:

My Energy Diary — Sample for One Day

| Time | Activity | Energy Used | Source |
|------------|-------------------------------|-------------|------------------|
| 6:30 AM | Switched on bathroom light | Electricity | Electric supply |
| 7:00 AM | Breakfast cooked on stove | Heat | LPG / Cooking gas|
| 7:30 AM | Watched TV for 30 minutes | Electricity | Electric supply |
| 8:00 AM | Travelled to school by bus | Movement | Diesel (Fuel) |
| 12:00 PM | Ate lunch (got energy to play)| Food energy | Food |
| 4:00 PM | Used fan while studying | Electricity | Electric supply |
| 7:00 PM | Switched on lights at home | Electricity | Electric supply |
| 8:00 PM | Dinner cooked on stove | Heat | LPG / Cooking gas|

Total count for the day:
- Electricity used: 5 times
- Fuel (LPG) used: 2 times
- Diesel (vehicle): 1 time
- Food energy: 2 times (lunch and dinner)

Conclusion: We use energy in many forms throughout the day. Being aware of how much energy we use helps us find ways to save energy and use it more wisely.

*(Students should fill in their own actual activities for the day.)*