1. Force : Push or pull which acts on an object. 2. Gravity : Force that pulls everything towards the earth. 3. Friction : Force that opposes the movement of a body. 4. Solar energy : Energy which is obtained from the sun. 5. Atomic energy : Energy which is obtained from the splitting of an atom. 6. Pulley : A set of wheels over which a rope or chain is pulled to lift heavy objects. 7. Screw : A thin pointed piece of metal with a raised spiral line.
Points to Remember
+ A push or pull which acts on an object is called force. + There are two types of forces in nature-gravity and friction. + There are also other types of forces-magnetic force, electrical force, etc. + A particular work is done when we use force on an object and it moves to a distance. + Energy is the capacity to do work. Sun, water, wind and atoms are some of the sources of energy. + Machines make our work easier. + There are different types of machines - wheel and axle, inclined plane, screws, wedges and levers.
Answer the following questions:
1. What do you mean by force ? Why do we use force?
A pull or push which acts on an object is called force.
We use force to stop or to move an object. We also use it to change the direction or position of an object. force can increase or decrease the speed of an object.
2. How is frictional force important in our life?
Frictional force plays a very important role in our lives. It is the frictional force that causes moving vehicles such as cycle, scooter, bus etc. to stop. When we apply the brakes of a cycle, the frictional force between the brakes and wheel cause the cycle to stop.
3. What are the different sources of energy?
The different sources of energy are- Sun Water Wind Atom Fossil fuels
4. What is atomic energy ?
Atomic energy is the energy that we get from splitting of an atom.
5. Which simple machines help us in our daily work?
We use many kinds of simple machines like wheel and axle, the inclined plane, screws, pulleys, wedges and levers.
6 How are fossil fuels beneficial for us?
Fossil fuels such as coal, petroleum and natural gas are good sources of energy. These fuels have energy stored in them. This energy can be released by burning the fuels. i) Coal is mostly used to generate heat. ii) Petrol and diesel are used to run vehicles. iii) kerosene and natural gas are used to get light and heat.
7. Give reasons why solar energy is an important form of energy.
i) We get heat and light from the sun. Green Plants use solar energy to prepare their food. ii) The heat of the sun helps in maintaining the water cycle... iii) Solar cells are used as batteries in various instruments.
Fill in the blanks:
1. Energy is the capacity to do work. 2. Pull and push are examples of Force. 3. Gravity pulls objects towards the center of the earth. 4. Atomic energy comes from the splitting of an atom. 5. Energy produced by waves is called tidal energy. 6. Kineticenergy is possessed by a body due to its motion. 7. Coal and petroleum are fossil fuels. 8. Pulley is a simple machine.
Name the following:
1. A machine which consists of a wheel with a rope around it: Pulley 2. Energy which is obtained from the sun: Solar energy 3. The force that opposes the speed of an object on a surface: Fiction 4. The force that we apply by our muscles: Muscular force 5. The rod which is used between wheels: Axle
Write T' for true and 'F' for false statements given below
1. When we lift something, it is called gravity. [F] 2. The sun is the main source of energy. [T] 3. Moving water has no energy at all.[F] 4. We get heat and light from the moon. [F] 5. Atom is useless as it cannot produce any energy.[F] 6. Tools make our work difficult.[F] 7. Wedge is a complex machine.[F] 8. A stretched bow has kinetic energy as well as potential energy. [F]
Think and answer:
1. What would happen if the earth had no gravity?
If Earth had no gravity, objects and people would no longer be pulled towards its center. Everything, including us, would float into space, making it impossible to stay on the ground or hold things down. This would drastically change the way we live, walk, and interact with our surroundings, causing chaos and disruption.
2. What would happen if there was no sun to give us light and heat?
The absence of the sun's light and heat would have a profound impact on Earth. Darkness would engulf our days, and temperatures would plummet, making it extremely cold. Plants would struggle to grow, and animals, including us, would face challenges in finding food and surviving. The sun is essential for life as we know it, providing energy and warmth that are crucial for sustaining ecosystems.