Class 8 Science Lesson 12 Inside Question and Answer NCERT & CBSE Board Here in this post. NCERT Class 8 Science Textbook Lesson 12 Inside Questions.
- Grade: VIII
- Lesson 12 Friction
Que. 1) fill in the blanks.
(1) The substance reduces friction are called —–
Ans- Lubricants.
(2) The frictional force exerted by fluids is also called—–
Ans- drag
(3) The static friction is slightly —— than sliding friction.
Ans- greater.
(4) Friction is caused by the ——– on the —— surface in contact.
Ans- irregularities, two.
(5) Friction is —- if a surface is rough.
Ans- greater.
Que. 2) answer the following.
(1) What is spring balance?
Ans- spring balance is a device used for measuring the force acting on an object. It consist of a coiled spring which gets stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force.
(2) What happed when we rub our palms together?
Ans- when we rub our palms together for a few minutes it produces heat.
(3) What is fluid friction? Explain.
Ans- fluid friction is the force of friction when objects move. The frictional force exerted by fluids is also called drag. The frictional force on an object in a fluid depends on its speed with respect to the fluid. The frictional force also depends on the shape of the object and the nature of the fluid. the objects move through fluids they overcome friction acting on them. All vehicles are designed to have shapes which reduces fluid frictions.
(4) What is lubricants?
Ans- the substance which reduces the friction are called lubricants. In some machines , vehicles, for avoiding frictions lubricants are used.
(5) Friction is caused by irregularities of two surface. Explain.
Ans- friction is caused by the irregularities on the two surfaces in contact. Even those surface which appears very smooth have a large number of minute irregularities on them. On the rough surfaces there are a larger numbers of irregularities so the force of friction is greater if a rough surface is involved.