Chapter 4: Force, Work and Energy
Descriptive Questions
- Q: What is friction?
- A: The force that opposes the motion of an object is known as frictional force. A ball stops rolling on the floor due to the opposing friction that acts on it.
- Q: List different forms of energy.
- A: Different forms of energy are mechanical, light, magnetic, sound energy, geothermal energy and atomic energy.
- Q: Why is geothermal energy referred to as a renewable source of energy?
- A: The energy we get from the earth is geothermal. The earth is very hot from inside and the steam and hot water are used to generate electricity. This source of energy can be renewed or replenished and hence is a renewable source of energy.
- Q: List the different types of force.
- A: Different types of force are frictional force, magnetic force, electrostatic force, gravitational force, muscular force and mechanical force.
- Q: Write a note on wind energy and solar energy.
- A: Wind energy: The energy that we get from wind. It is used to generate electricity by running the windmill. Solar energy: The energy that we get from the sun. We use it to cook food, produce heat and light energy, and it is used in solar watches, solar calculators and solar cars.
- Q: Differentiate between renewable and non-renewable sources of energy.
- A: Renewable sources of energy can be renewed or replenished (e.g., wind, solar, geothermal and hydro energy). Non-renewable sources of energy cannot be renewed or replenished (e.g., coal, petroleum and natural gas) as they take millions of years to form.
- Q: With the help of suitable examples, discuss when work is done, and when it is not done.
- A: When we push a ball or a chair, it moves in the direction in which the force is applied; work is said to be done. Suppose you are pushing a wall and the wall does not move, no work is said to be done.
Objective Questions
- Fill in the blanks:
- Pushing or pulling an object is called force.
- The energy we get from the earth is geothermal energy.
- To move an object we need to apply force.
- Wind energy is used to generate electricity by running the windmill.
- True or False:
- The ability to do work is called force: False
- Things can move without any force acting on them: False
- Energy is necessary to do work: True
- Wind energy is a non-renewable source of energy: False
- Answer in one word:
- The energy that we get from water: Hydro
- The device that uses solar energy: Solar car
- A source of energy which can be renewed: Renewable
- A non-renewable source of energy: Coal