# Tamil Nadu Board Class 8 Science Chapter 2 Force and Pressure

if you are looking for Tamil Nadu Board Class 8 Science Chapter 2 Force and Pressure then you are at the right place. Here we are providing solutions as well as additional QA / Important Notes.

Choose the best answer.

If we apply force against the direction of motion of the 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

Pressure exerted by a liquid is increased by

• a) the density of the liquid
• b) the height of the liquid column
• c) Both a and b
• d) None of the above

Unit of pressure is

• a) Pascal
• c) Poise
• b) Nm
• d) Both a and b

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

Pascal’s law is used in

• a) hydraulic lift
• b) brake system
• c) pressing heavy bundles
• d) All the above

Which of the following liquids has moviscosity?

• a) Grease
• c) Coconut oil
• b) Water
• d) Ghee

The unit of viscosity is

a) Nm2 b) poise c) kgms1 d) No unit

Fill in the blanks.

1.  The pressure of a liquid column ________with the depth of the column.[increases]
2.  Hydraulic lift works under the principle of ________ [pascal’s law]
3.  The property of ____ of a liquid surface enables the water droplets to move upward in plants.[surface tension]
4.  A simple barometer was first constructed by __________ [torricelli]

III. State true or false. If false, correct the statement.

1. Force acting on a given area is called pressure.[True]
2. A moving body comes to rest due to friction alone.[False – A moving body comes to rest due to friction and possibly other forces like air resistance.]
3. A body will sink if the weight of the body is greater than the buoyant force.[True]
4. One atmosphere is equivalent to 1,00,000 newton force acting on one square metre.[False – One atmosphere is equivalent to 1,00,000 pascals of pressure acting on one square metre.]
5. Rolling friction is slightly greater than the sliding friction.[False. Rolling friction is less than sliding friction.]
6. Friction is the only reason for the loss of energy. [False. Friction is one reason for the loss of energy, but not the only reason. Energy can also be lost due to other factors such as air resistance, heat, and sound.]
7. Liquid pressure decreases with the decrease of depth.[True]
8. Viscosity depends on the pressure of a liquid.[False. Viscosity primarily depends on the temperature of a liquid, not its pressure.]

Match the following.

A

• Static friction  –  Viscosity
• Kinetic friction –  Least friction
• Rolling friction –  Objects are in motion
• Friction between the liquid layers – Objects are sliding
• Sliding friction – Objects are at rest

Solution-

• Static friction – Objects are at rest
• Kinetic friction – Objects are in motion
• Rolling friction – Least friction
• Friction between the liquid layers – Viscosity
• Sliding friction – Objects are sliding

B

• Barometer – reduce friction
• Increasing area of contact – Atmospheric pressure
• Decreasing area of contact – cause of friction
• Lubricants – increases friction
• Irregular surface – decreases friction

Solution

• Barometer – Atmospheric pressure
• Increasing area of contact – decreases friction
• Decreasing area of contact – increases friction
• Lubricants – reduce friction
• Irregular surface – cause of friction

Complete the analogy.

•  Knot in a thread:_____friction:: Ball bearing:______friction
•  Downward force: Weight :: Upward force offered by liquid:____

Solution-

• Knot in a thread: Increased friction :: Ball bearing: Decreased friction
• Downward force: Weight :: Upward force offered by liquid: Buoyant force

VII. Consider the statements given below and choose the correct option.

Assertion: Sharp knives are used to cut the vegetables. Reason: Sharp edges exert more pressure.

Ans – Both assertion and reason are true and reason is the correct explanation of assertion.

Assertion: Broad straps are used in bags. Reason: Broad straps last for long.

Ans – Assertion is true, but reason is false.

Assertion: Water strider slides easily on the surface of water.Reason: Water strider experiences less buoyant force.

Ans- Assertion is true, but reason is false.

VIII. Answer very briefly.

Give two examples to verify that a force changes the shape of a body.

Squeezing a rubber ball: When you squeeze a rubber ball, its shape changes due to the applied force.

Stretching a spring: When you pull or compress a spring, its shape changes.

Give two examples to verify that a force tends to change the static condition of a body.

Pushing a stationary car: When you push a car at rest, it starts to move, changing its static condition.

Kicking a football: When you kick a football lying on the ground, it starts to roll, changing its state from rest to motion.

How do you feel when you touch a nail immediately after it is hammered into a wooden plank? Why?

You feel heat when you touch the nail because hammering generates friction between the nail and the wood, converting kinetic energy into thermal energy.

How does the friction arise between the surfaces of two bodies in relative motion?

Friction arises due to the microscopic irregularities on the surfaces of the two bodies in contact. These irregularities interlock and resist relative motion.

Name two instruments which help to measure the pressure of a fluid.

Barometer: Measures atmospheric pressure.

Manometer: Measures the pressure of a fluid in a closed system.

Define one atmosphere.

One atmosphere (1 atm) is the pressure exerted by a mercury column of height 76 cm in a barometer at sea level, equivalent to 101,325 pascals (Pa).

Why are heavy bags provided with broad straps?

Heavy bags are provided with broad straps to distribute the load over a larger area of the shoulders, reducing the pressure and making it more comfortable to carry.

How does surface tension help a plant?

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