Force, Work and Energy Class 4 Notes Science

Force

Force is when you push or pull something. It can make things move, stop, or change shape. For example, when you kick a ball, you're using force to make it move. Forces are everywhere and help us do lots of things every day, like opening a door or riding a bike.

Types of Forces

There are many different types of forces. Let us study some that we come across often in our daily lives.

Friction

Friction is a force between two surfaces which are in contact. Roll a ball on the ground. It slows down and stop. Why does it not keep going?

• It stops because friction acts on it. 
• The ball will go further on a smooth surface than on a rough surface. 
• This is because the force of friction is more on rough surfaces. It is less on smooth surfaces.
• If the box is kept on a smooth surface, less force is required to move it. 
• If the box is kept on a rough surface, greater force is required to move it. This is because of friction.

• Throw up a ball. Observe it carefully. It slows down, stops, and then comes down. Why doesn't it keep going up? 
• This is because gravitational force pulls everything down. 
• You can stand on the ground because gravity pulls you down. If there was no gravity we would all be floating in the air.

  
  

Muscular Force

Magnetic Force

A magnet applies a force on things made of iron and steel and pulls them towards itself.

• This force is called magnetic force.

• The magnet does not pull things made of other substances such as paper, plastic.

Disadvantages of Friction

• Friction wastes energy because it makes it difficult for things to move.
• The soles of your shoes wear away after some time because of friction.
• Friction causes parts of the moving machine to wear out.

Advantages of Friction

• We can walk because of friction between our feet and the ground. 
• Without friction, we will slip and fall. 

Have you ever tried to walk on ice? Why is it difficult? Ice is very smooth, so there is very little friction and you can slip easily.
Cars and buses can run on roads because of friction between the tires and the road. Sometimes, cars slip on wet roads because the friction is less.

Reducing Friction

Activity - Take a carrom board. Place the striker on it and shoot it with your fingers. See how far it goes before it stops.
Now spread talcum powder all over the board. Again, hit the striker with the same force. See how far it goes now. Does it go further? Why?

• Talcum powder is smooth. It reduces the friction on the board, so the striker travels further.
  
  Reducing friction
• Oiling reduces friction between surfaces because it makes the surfaces smooth. If you put oil on the moving parts of your bicycle, it will run more smoothly. Oiling is done in machines in functions. It saves parts of machines from wearing out soon.

Oiling in machines

What is Work?

You already know that a push or a pull is called force. A force can make things move. When a force moves something, work is done.

• When you open a door you do work. When you kick a football you do work. Look at the given pictures. The man is pulling a cart. Thus, the work is done.
• However, in the second case, the boy is pushing a wall. The wall does not move.
  Thus, the work is not done in this case. This is because, there is insufficient force being applied on the wall, which does not move it. 
• On the other hand, if we apply a greater force on the wall, say using a crane, the wall will break. Thus, in that case work will be done.
  
  Work done

No work done

Simple Machines

We use some tools in our everyday life that make our work easier. These tools are called simple machines. Let's learn about some of them: 

1. Lever

A lever is a simple machine used to lift or move heavy weights, open the lid of a tin, or cut things. Examples of levers are see-saws, bottle openers, and scissors.

• Example: When you use a spoon to open a lid, the spoon acts as a lever or a sissor.

2. Inclined Plane

An inclined plane is a slope that helps move heavy objects to a higher place easily. Heavy cartons are loaded onto a truck by pushing them up on an inclined wooden plank. Ramps, slanted roads, and slides are examples of inclined planes.

• Example: Slide

3. Screw

A screw looks like a nail but has an inclined plane wrapped around a cylinder. It has a broad head and pointed tip and is used to hold things together.

• Example: Light bulb

4. Wedge

A wedge is a simple machine made of two inclined planes joined to form a sharp edge. It is used to cut things. Axes and knives are examples of wedges.

• Example: Axe

5. Wheel and Axle

In a wheel and axle arrangement, a rod (axle) passes through the wheel, helping it turn. This setup helps move heavy objects. Screwdrivers, steering wheels, and vehicle wheels are examples of wheel and axle.

• Example: Bicycle

6. Pulley

A pulley consists of a grooved wheel and a rope. It is used to lift heavy loads easily.

• Example: Crane

Energy

When you do work, you use energy. How do you feel after doing a lot of work? Do you feel tired? From where can you get more energy? You can get energy from food.

• Energy is the ability to do work.
• Energy is required to change ice to water, or water to steam, or wood to smoke and ash.

Forms of Energy

There are many forms in which we get energy. Some of these are as follows.

Sources of Energy

• Sun: The sun gives us solar energy. Plants use this energy to make food, and we can use it to cook food in solar cookers or heat water.
• Wind: Wind energy helps boats sail and windmills generate electricity.
• Water: Water energy, or hydropower, generates electricity.
• Fuel: Fuels like wood, petrol, and LPG are burned to produce energy.

Let us look at some of the main sources of energy.

Sun as a Source of Energy

Sun is the greatest source of energy on Earth. The energy from the sun is called solar energy.
Plants use this light energy to make food for the entire living world. So, the energy we get from food also comes from the Sun.
Today we have discovered many other uses of solar energy, for example- 

• Food can be cooked in solar cookers. They use sun’s energy to cook food.
  
  Solar cooker
• Solar energy is often used to heat water in solar water heater.
• Solar power is the conversion of energy from the sun into electricity. It can be used to run air conditioners, water heaters, and everything that runs on natural gas, electricity. It’s a cheaper, safer, and more eco-friendly solution.
  
  Solar panel charges solar batteries
• Solar batteries are used to light up calculators, watches and bulbs.

Wind Energy

The air or wind that blows has energy. This wind energy is used to help a boat sail and turn the shafts of a windmill. The turning shaft of the windmill provides power to a machine called a generator to produce electricity.
Windmill

Water Energy

Water is another very important energy source. People, plants and animals all depend on water.
Hydropower is energy that comes from the force of moving water. Like wind energy, water energy helps to generate electricity.
Water dam

Fuel Energy

Things which can be burnt to produce energy, such as wood, petrol, coal or LPG are called fuels. Fuels are burnt to produce heat and power.
Energy is stored in wood. When wood is burnt, this energy is given out as light and heat. LPG (Liquid Petrolium Gas, the ‘gas’ we use at home to cook food) has stored energy too. Petrol, diesel and CNG (Compressed Natural Gas) are used to run vehicle and machines.
Fuels

Concluion

energy is essential for all activities and changes around us. It powers our bodies, machines, and the natural processes that sustain life. By understanding the various sources of energy, like the sun, wind, water, and fuels, we can better appreciate how integral energy is to our everyday lives and the world around us.

Important Points

1. A push or a pull is called a force.
2. Force can move an object, stop a moving object, change the direction and speed of a moving object, or change the shape of an object.
3. Gravity of the earth pulls everything towards itself.
4. Friction is the force between two surfaces in contact.
5. Work is done when a force moves an object.
6. Energy is required to do work or to change matter.
7. There are various forms of energy—heat, light, electrical and sound energies.
8. Energy can be stored for later use.
9. Sun is the main source of energy.