Question

3. Why are the dams over river made broader at the bottom than at the top?
Give three methods of reducing friction.
4. Give three methods of reducing friction.
5. Why is friction a necessary evil? Explain.
6. On what factors does the limiting value of the force of static friction depen
7. What do you mean by the resultant force?
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Answer 1

Answer:

3) The deeper the river goes the stronger is the pressure. That is pressure of water is the strongest at the bottom

4)There are a number of ways to reduce friction:

Make the surfaces smoother.

Lubrication is another way to make a surface smoother.

Make the object more streamlined.

Reduce the forces acting on the surfaces.

Reduce the contact between the surfaces.

Roll the bodies instead of sliding them.

5)Frictional force causes a lot of losses in general upkeep and wear and tear of machinery.Hence it is considered a evil.  But almost all crucial tasks cannot be carried out without the presence of friction. Basic activities like walking and writing on a surface are possible due to friction. Hence it is considered as a necessary evil .

6) The limiting coefficient of static friction between two surfaces depends on the two surfaces, and as such, should be the same for the same pair of surfaces. However, the coefficient depends on a number of factors such as dampness, adherence of dust to the surfaces, scratches, or minor surface changes, hence the measurement for the same pair of surfaces may differ with time.

7) A resultant force, also called a net force, is a force equal to the sum of all forces applied to an object.

Answer 2

Answer:

1. The reason is that the pressure increases as we go deeper and deeper into the water. So, the pressure is greatest at the bottom of the water. So, to withstand the pressure, dams are made broader at the bottom.

Explanation:

1. 4)There are a number of ways to reduce friction:

• Make the surfaces smoother. ...
• Lubrication is another way to make a surface smoother.
• Make the object more streamlined. 5)Friction is said to be a necessary evil because it is useful as well as harmful. friction helps us to walk, write, hold things, lift objects. So it is necessary in our lives. 6)Without friction many essential processes can not be done. The limiting coefficient of static friction between two surfaces depends on the two surfaces, and as such, should be the same for the same pair of surfaces. 7)A resultant force is the single force and associated torque obtained by combining a system of forces and torques acting on a rigid body. The defining feature of a resultant force, or resultant force-torque, is that it has the same effect on the rigid body as the original system of forces