Force and Pressure

Samacheer Book Back Questions And Answers For Science Standard 8 “Forces and Pressure“

I. Choose the best answer:
1.If we apply a force against the direction of motion of a body, then the body will _____.
(a) Stop moving
(b) Move with an increased speed
(c) Move with a decreased speed
(d) Move in a different direction

2. Pressure exerted by a liquid is increased by _____.
(a) The density of the liquid
(b) The height of the liquid column
(c) Both (a) & (b)
(d) None of the above

3. Unit of pressure is _____.
(a) Pascal
(b) N m-2
(c) Poise
(d) Both (a) & (b)

4. The value of the atmospheric pressure at sea level is _____.
(a) 76 cm of mercury column
(b) 760 cm of mercury column
(c) 176 cm of mercury column
(d) 7.6 cm of mercury column

5. Pascal’s law is used in _____.
(a) Hydraulic lift
(b) Brake system
(c) Pressing heavy bundles
(d) All the above

6. Which of the following liquids has more viscosity?
(a) Grease
(b) Water
(c) Coconut oil
(d) Ghee

7. The unit of viscosity is _____.
(a) Nm²
(b) Poise
(c) kg m s^-1
(d) No unit

II. Fill in the blanks:
1. The pressure of a liquid column _____ with the depth of the column.
2. Hydraulic lift works under the principle of _____.
3. The property of _____ of a liquid surface enables the water droplets to move upward in plants.
A simple barometer was first constructed by _____.

Answers:
1. Increases
2. Pascal’s Law
3. Surface tension
4. Torricelli

III. State whether the following statements are true or false:
1. Force acting on a given area is called pressure.
2. A moving body comes to rest due to friction alone.
3. A body will sink if the weight of the body is greater than the buoyant force.
4. One atmosphere is equivalent to 1,00,000 newton force acting on one square metre.
5. Rolling friction is slightly greater than the sliding friction.
6. Friction is the only reason for the loss of energy.
7. Liquid pressure decreases with the decrease of depth.
8. Using barometers, one can measure the height of a building.
9. Surface tension causes the spherical nature of a water drop.
10. Viscosity depends on the pressure of a liquid.

Answers:
1. True
2. True
3. True
4. True
5. False (Rolling friction is slightly lesser than the sliding friction)
6. True
7. True
8. False (Using barometers, one can measure the atmospheric pressure)
9. True
10. True

IV. Arrange the following in the increasing order:
1. Rolling friction, static friction, sliding friction
2. Let a marble roll on the following surfaces. Arrange the choice of the material such that a marble moving over it covers a greater distance.
Cotton cloth, glass plate, paper, card board, silver plate

Answers:
1. Static friction, Rolling friction, Sliding friction.
2. Glass plate, silver plate, paper, cotton cloth, card board.

V (A). Match the following:
1. Static friction                                      A. Viscosity
2. Kinetic friction                                    B. Least friction
3. Rolling friction                                    C. Objects are in motion
4. Friction between the liquid layers      D. Objects are sliding
5. Sliding friction                                    E. Objects are at rest

Answers:
1. E
2. C
3. B
4. A
5. D

V (B). Match the following:
1. Barometer                              A. Reduce friction
2. Increasing area of contact      B. Atmospheric pressure
3. Decreasing area of contact    C. Cause of friction
4. Lubricants                               D. Increases friction
5. Irregular surface                     E. Decreases friction

Answers:
1. B
2. D
3. E
4. A
5. C

VI. Analogy:
1. Knot in a thread : _____ friction :: ball bearing : friction _____
2. Downward force : weight :: Upward force offered by liquid : _____

Answers:
1. Rolling, Static.
2. Buoyant force.

VIII. Assertion & Reason:
1. Assertion: Sharp knives are used to cut the vegetables.
Reason: Sharp edges exert more pressure.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.

2. Assertion: Broad straps are used in bags.
Reason: Broad straps last for long life.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Reason: Pressure will be low.

3. Assertion: Water strider slides easily on the surface of water.
Reason: Water strider experiences less buoyant force.
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Reason: Due to surface tension.

Visit Our YouTube Channel For More Free Videos: Click Here