LESSON NOTES:-

FORCE, WORK AND ENERGY

Fill in the blanks:-

  1. Our main source of energy is the sun
  2. Food gives us energy to work.
  3. A push or a pull is called a force.
  4. The standard unit of force is Newton.
  5. Volume of liquids express in liter
  6. I cm3= 1 ml
  7. Standard unit of energy isJoule.
  8. Energy is the ability of doing work.
  9. Scissor is a kind of lever.
  10. To stop a moving object we need to applyforce.

Name the following:-

1. Force that pulls everything down -gravity

  1. The measure of space occupied by an object. - volume
  2. The amount of substance present in an object - density
  3. Name the force that helps us to walk on the ground without slipping -friction
  4. The standard unit of work -joule
  5. Energy used for photosynthesis -solar energy
  6. When force move an object from one place to another - work
  7. A fossil fuel -petrol, coal
  8. A simple tool that make our work easier -simple machine
  9. Energy that comes from the splitting of an atom - nuclear energy

Give reason:-

  1. Base of a dam is broader than the top. Why?

Ans. This is because pressure of a liquid increases with depth.

  1. Why do we sprinkle talcum powder on a carom board?

Ans. We sprinkle talcum powder on the carom board to reduce the friction. This enables the coin to move freely on the board.

  1. Work is not done when we push a wall. Why?

Ans. A work is said to be done only if the applied force can move the wall.

Answer the following:-

  1. What is a force? List out a few things which force can do.

Ans. The cause of motion is called force. It gives the feeling of push and pull.

  • Force can move an object
  • Force can stop a moving object
  • Force can change the direction of motion
  • Force can change the speed of a moving object.
  • Force can change the shape of an object
  1. What are machines?

Ans. A machine is a tool which makes our work easier, and increases speed of doing work. Some machines help to change the direction of applied force.

  1. Define work.

Ans. Work is said to be done if a force can move an object through a distance.

Work= force × distance

  1. How is friction useful?

Ans. Friction is helpful in many ways:-

  • Friction holds your shoe to the ground, allowing you to walk
  • We could not hold a pencil in your hand without friction
  • We could not stop a car without the friction of the brakes and the tires
  1. Define density.

Ans. Density is the amount of substance present in unit volume.

  1. Define pascal’s law of fluid pressure.

Ans. The Pascal’s law states that all the fluids exert pressure equally in all directions.

  1. A Special quality of energy is that it can be convert from one form to another. There are some appliances given below, mention they convert which form of energy into which form.
  • Electric oven: converts electrical energy into heat.
  • Fan : converts electrical energy into mechanical energy.
  • Hand pump: converts muscular energy into mechanical energy
  • Electric engine: converts electrical energy into mechanical energy.