Work and Energy class 5 icse

 

Work and Energy

WORK

When we pull or push an object force is applied. When force is applied on a body, it begins to move and travels a certain distance. In this case, work is said to be done.

When we use force to move things from one place to another, we do work. The amount of work done by a moving body can be measured by measuring the distance covered by it and the force applied to it.

Pushing a chair is easy, but pushing a cupboard full of books is difficult. It requires more force to move the cupboard. So the work done in moving the cupboard is more than the work done in moving the chair.

Some examples of work done are pushing a trolley, a pair of bullocks pulling a plough in a field, a person pressing a switch and an electric fan beginning to move, and birds flying in the sky.

Thus, we can say that when a body is displaced by force, work is said to be done. However, when we apply a force on an object and it does not move, no work is done. For example, if we push a wall and the wall does not move, no work is done.

ENERGY

Work and energy are closely related to cach other. Energy is the ability or capacity to do work. We all need energy to do work. There are different sources of energy. For human beings, plants and animals, the energy to work is obtained from food.

Renewable and Non-renewable Sources of Energy

Sources of energy are of two types- renewable sources of energy and non-renewable sources of energy.

Biomass energy

Hydropower Wind

energy energy

Energy

Geothermal energy

Solar energy

Energy

Fossil fuel oil

Natural gas

Coal

Nuclear

The sources of energy that can be renewed or replenished over a long period of time are called renewable sources of energy. The energy obtained from these sources is known as renewable energy. Solar energy, wind energy, geothermal energy, biomass and hydropower are examples of renewable energy.

Renewable energy and their sources

Sources of non- renewable energy

The energy sources that are present in limited quantity in nature and will not last for a long time are called non-renewable sources of energy. Some examples of these energy sources are coal, petroleum and natural gas. The energy obtained from these sources is known as non-renewable energy.

FORMS OF ENERGY

Energy exists in different forms. Let us learn about these different forms of energy.

Mechanical Energy

The energy that an object possesses due to its position and movement is called mechanical energy. Mechanical energy is further divided into two types, kinetic energy and potential energy.

A moving vehicle possesses mechanical energy due to its motion. This type of mechanical energy is called kinetic energy. A stretched bow possesses energy due to its (stretched) position. This type of mechanical energy is called potential energy.

Geothermal Energy

The word geo means Earth and therme means heat. Thus, geothermal energy is the energy obtained from the Earth's core. The steam and hot water from inside the Earth or the Earth's core are used to generate electricity. Geothermal energy is a renewable energy source because its source is the unlimited amount of heat generated by the Earth's core.

Solar Energy

The light and heat energy that we get from the Sun is called the solar energy. The Sun is the ultimate source of energy on the Earth. Solar energy is a renewable source of energy and is easily available. Solar energy can be used to cook food, heat water and also to generate electricity.

 

Wind Energy

The moving air is called wind. The energy possessed by the moving air is called the wind energy. Wind energy is clean, easily available and it is a renewable source of energy. It is used to move windmills to generate electricity and to grind grains.

Hydropower or Hydroelectric Energy

A windmill

Hydropower or hydroelectric energy is the energy obtained from moving water.

It is also a renewable source of energy which is used to generate electricity. To use hydro energy, water is collected in a lake behind a dam and dropped from a height to turn the turbines which move the generator and produce electricity.

Electrical Energy

We use electrical energy to run various appliances like washing machines, television computers, ovens, fridges, tube lights, fans, etc., at home. Today, life without electricity is hard to imagine. Most modern-day appliances run on electricity. We should always save electricity and switch off electrical appliances when not in use

 

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Heat Energy

The Sun is the ultimate source of heat energy. Heat energy can also be released by barning fuels like coal, petroleum, oil, gas, wood, etc. This energy is used to generate steam, cook food, dry clothes, etc.

Light Energy

Light energy helps us see things around us. The Sun is a natural source of light energy.

Sound Energy

Sound energy is produced when something vibrates. It helps us to hear. Our ears have the ability to recognise and differentiate between different types of sounds.

LAW OF CONSERVATION OF ENERGY

The law of conservation of energy states that energy can neither be created nor destroyed. It only gets converted from one form to other. For example, when we use electrical energy to light a bulb, the electrical energy does not get destroyed. Instead it gets converted into light energy and heat energy. There are many such examples where we can observe change of one form of energy to another
RELATION BETWEEN FORCE, WORK AND ENERGY

Force, work and energy are related to each other. We need energy to apply force on an object. When force is applied, the object moves from one place to another, and the work is done.

Energy Force Work

Let us understand this with the help of an example of a sportsperson.

Tennis players get energy from the food they eat. They use uses this energy to hit the ball on the court. This force moves the ball to the other side of the court to the other player. Thus, energy is used to exert force which results in work being done.

EXERCISES

A. Tick (✔) the correct answer.

1. Which of the following forms of energy is not directly linked to the Sun?

a. Wind

b. Solar

c. Biomass

d. Light

2. Which of the following is a non-renewable source of energy?

a. Solar

b. Wind

c. Coal

d. Hydro energy

3. Which of the following is the most easily available source of energy?

a Solar energy

b. Wind energy

c. Geothermal energy

d. Hydro energy

4. Which of the following activities is an example where work is done?

a.Swimming

b. Pushing a wall

c. Holding a bag

d. Sitting in a car

B. Fill in the blanks.

1. Pulling a bucket of water from a well is an example of _____work______.

2. Humans store energy from _______food_____

3. _____The Sun_______ is the major source of energy on the Earth.

4. Water falling from a height is used to get ___hydroelectric_________energy.

C. Match the following.

Term	Definition
1. Energy	b. Ability to do work
2. Force	e. Push or pull
3. Mechanical	d. Energy due to object's position or movement
4. Light	a. Helps us to see
5. Heat	c. Helps us to generate steam

 

D. Give reasons for the following.

 

1. We need to eat food to perform work.

·  We need to eat food to perform work because food provides us with energy. This energy is essential for our bodies to function, move, and carry out various activities. When we eat, our bodies break down the food into simpler substances, releasing energy that fuels our cells. This energy is then used to contract muscles, send nerve impulses, and perform other bodily functions, enabling us to do work.

 

2. A porter carrying a load on his head and standing at a place is not doing any work.

·  A porter carrying a load on his head and standing at a place is not doing any work because work is done only when a force is applied to an object, and that object moves a certain distance in the direction of the force. In this case, the porter is applying a force to hold the load, but the load is not moving. Therefore, no work is being done, even though the porter is exerting effort.

E. Answer the following questions in one word.

1. Which kind of force is used in the game of tug-of-war-push or pull?

·  Pull is the force used in the game of tug-of-war.  

2. Give any one example of an electrical appliance used in the kitchen.

Microwave oven is an example of an electrical appliance used in the kitchen.  

3. Give an example of a non-renewable source of energy.

Coal is an example of a non-renewable source of energy.  

4. In how many forms does mechanical energy exist?

·  Mechanical energy exists in two forms: kinetic energy and potential energy

 

F. Answer the following questions in brief.

1. List any three sources of heat energy.

·  Three sources of heat energy are:

• Sun: The primary source of heat energy on Earth.  
• Burning of fuels: Such as coal, natural gas, and petroleum.  
• Geothermal energy: Heat from the Earth's core.  

 

2. What are the effects of force?

·  Effects of force:

• Change in shape: A force can change the shape of an object, like squeezing a ball.  
• Change in direction: A force can change the direction of a moving object, like a football being kicked.  
• Change in speed: A force can increase or decrease the speed of a moving object, like accelerating a car.  
• Change in state of motion: A force can start or stop the motion of an object, like pushing a stationary box.  

3. How is electricity generated from hydro energy?

·  Hydroelectricity generation:

• Water is stored: Water is collected in a reservoir behind a dam.  
• Water is released: Water is released from the reservoir and flows through pipes.  
• Turbines are turned: The flowing water strikes the blades of turbines, causing them to rotate.  
• Generator is activated: The rotating turbines are connected to a generator, which converts mechanical energy into electrical energy.  
• Electricity is produced: The generator produces electricity, which is then transmitted to homes and industries.

 

 

 

 

G. Answer the following questions in detail.

1. What is the relation between work and energy? Give examples.

Relation between Work and Energy

Work and energy are intimately connected. Energy is the capacity to do work, while work is the application of force to move an object over a distance.  

• Energy is required to do work: To perform any task, we need energy. For instance, to lift a weight, our muscles require energy to exert the necessary force.  
• Work done results in energy transfer: When work is done, energy is transferred from one form to another. For example, when we pedal a bicycle, the mechanical energy from our legs is converted into kinetic energy of the bicycle.  
• Energy can be stored and released to do work: Energy can be stored in various forms, such as potential energy (stored energy) or kinetic energy (energy of motion). This stored energy can be released to do work, like a stretched rubber band releasing its potential energy to propel a toy car.  

 

2. What is the use of wind energy?

Use of Wind Energy

Wind energy is a clean and renewable source of energy that harnesses the power of the wind. It has various applications:  

• Electricity generation: Wind turbines convert the kinetic energy of the wind into electrical energy, which can be used to power homes, businesses, and industries.  
• Water pumping: Windmills can be used to pump water for irrigation and domestic use.  
• Mechanical power: Windmills can be used to grind grains, saw wood, and perform other mechanical tasks.  

 

3. Differentiate between renewable and non-renewable sources of energy.

3. Renewable vs. Non-Renewable Sources of Energy

• Renewable Sources of Energy:
• These sources can be replenished naturally over a relatively short period.  
• Examples include solar energy, wind energy, hydro energy, geothermal energy, and biomass energy.
• These sources are environmentally friendly and sustainable.  
• Non-Renewable Sources of Energy:
• These sources exist in limited quantities and take millions of years to form.
• Examples include fossil fuels like coal, oil, and natural gas.  
• Their use contributes to pollution and climate change.  

4. Write about any four forms of energy.

Four Forms of Energy

• Kinetic Energy: The energy possessed by an object due to its motion. Examples include a moving car, a flowing river, and a spinning top.  
• Potential Energy: The energy stored in an object due to its position or configuration. Examples include a stretched rubber band, a wound-up spring, and water stored behind a dam.  
• Thermal Energy: The energy associated with the random motion of atoms and molecules. It is related to temperature. Examples include heat from the Sun, a burning candle, and a hot cup of coffee.  
• Electrical Energy: The energy associated with the flow of electric charge. It is used to power various devices like lights, appliances, and computers.

 

Out of the Box

1. Solar energy can also be used at night when the Sun is not there. Do you agree? Give reasons to support your answer.

·  No, solar energy cannot be used at night when the Sun is not there. Solar energy is derived directly from sunlight, and without sunlight, solar panels cannot generate electricity. While there are technologies like solar batteries that can store energy generated during the day for nighttime use, the initial energy source is still sunlight.

2. How does a torch emit light though it is not connected to electricity?

·  A torch emits light through a chemical reaction. Inside the torch, there is a battery that provides electrical energy. This energy is used to activate a chemical reaction within the bulb. This reaction produces light energy, which is emitted through the transparent part of the bulb.

 

 

Worksheet

A. Read the statements given below and put a tick (✔) against the ones where work is done and a cross (X) against the rest.

1.      Raj pushed the football and a goal was scored. ✔

2.      Ram pushed a heavy rock and it did not move. X

3.      Jane is standing at the bus stop holding a bag. X

4.      Nida is coming down the slide. ✔

5.      Jasmeet is pushing a wall. X

B. Write an example each for the following forms of energy.

1.      Potential energy: A stretched rubber band ready to be released.

2.      Hydropower: Water stored behind a dam, ready to be released to turn turbines and generate electricity.

3.      Electrical energy: A light bulb glowing, powered by electricity.

4.      Geothermal energy: Hot water and steam from beneath the Earth's surface, used to generate electricity.

C. Read the statements for Assertion and Reason carefully, and choose the correct interpretation from the options that follow:

Assertion: It is important to conserve fossil fuels.

Reason: Fossil fuels are non-renewable sources of energy.

1. Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

2. The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

3. Assertion is true but the Reason is false.

4. Assertion is false but the Reason is true.

5. Both the statements are false.

 

1. Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.

Fossil fuels are limited resources that take millions of years to form. Conserving them is crucial to ensure their availability for future generations and to reduce our reliance on these polluting energy sources.