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NCERT 8th Class (CBSE) Science: Force and Pressure

NCERT 8th Class (CBSE) Science: Force and Pressure

Question: What two things fully describe a force?

Answer: Two things that fully describe a force in push and pull.

Question:If several forces act in different directions on a body, in which direction will the body move?

Answer: When two or more forces act on an object in different directions, the effect on the object is due to the magnitude and direction of the net force acting on it.

Question: If object is thrown up, it finally comes down. Why?

Answer: If an object is thrown up, it finally comes down because of the force of gravity. Gravity is the force with which the earth pulls everything towards itself.

Question: What is the difference between mass and weight?

Answer: The difference between mass and weight is as follows:

Mass
Weight
1. Mass is the quantity of matter contained in the body.
1. Weight is the force of gravity acting on the body.
2. It is measure of inertia of the body.
2. It is measure of gravity.
3. Mass is scalor quantity.
3. Weight is vector quantity.
4. Mass is expressed in (Kg) Kilogram.
4. Weight is expressed in Newton (N).
5. It only has magnitude.
5. It has magnitude as well as direction.

Question: Why can a magnet act from a distance?

Answer: It can act from a distance because it is surrounded by an invisible field of magnetic force.

Question: What is pressure? What does pressure depends on?

Answer: Pressure is force unit per area. Pressure depends on two factors:

  1. The magnitude of force applied – the greater the force, the greater is its effect.
  2. The area over which the force is applied, i.e. the area of contact between the two objects.

Question: What is atmosphere pressure? What is it caused by?

Answer: The pressure exerted by air is called atmospheric pressure. It is caused by the air above us which presses down on us with a force equal to that exerted by a mass of 1 kg, on every square centimeter.

Question: Why is it difficult to cut vegetable with a blunt knife?

Answer: When the knife is blunt the area of contact becomes larger which results into effect of the force. Thus it is difficult to cut vegetables with a blunt knife.

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