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.
- The pressure of a liquid column ________with the depth of the column.[increases]
- Hydraulic lift works under the principle of ________ [pascal’s law]
- The property of ____ of a liquid surface enables the water droplets to move upward in plants.[surface tension]
- A simple barometer was first constructed by __________ [torricelli]
III. State true or false. If false, correct the statement.
- Force acting on a given area is called pressure.[True]
- 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.]
- A body will sink if the weight of the body is greater than the buoyant force.[True]
- 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.]
- Rolling friction is slightly greater than the sliding friction.[False. Rolling friction is less than sliding friction.]
- 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.]
- Liquid pressure decreases with the decrease of depth.[True]
- 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?
Surface tension aids in capillary action, helping water to rise through the narrow xylem vessels from the roots to the leaves against gravity.
Which has greater viscosity, oil or honey? Why?
Honey has greater viscosity than oil because its internal friction between its layers is higher, making it flow more slowly.
Answer briefly.
Define friction. Give two examples of the utility of friction in day to day life.
Friction is the force that opposes the relative motion or tendency of such motion of two surfaces in contact. It acts in the opposite direction of the moving object.
Examples:
Walking: Friction between our shoes and the ground allows us to walk without slipping.
Writing: Friction between the pen and paper allows us to write.
Mention any three ways of minimising friction.
Using lubricants: Applying substances like oil or grease between moving parts reduces friction.
Using ball bearings: Ball bearings convert sliding friction into rolling friction, which is significantly lower.
Streamlining: Designing objects like cars and airplanes with smooth, streamlined shapes reduces air resistance (a type of friction).
State Pascal’s law and mention its applications.
Pascal’s Law: Pascal’s law states that the pressure applied to any point of a confined fluid at rest is transmitted undiminished in all directions throughout the fluid.
Applications:
Hydraulic lift: Used in car service stations to lift vehicles.
Hydraulic brakes: Used in vehicles to provide braking force.
Hydraulic press: Used to compress materials like cotton or cloth bundles.
Why is a ball bearing used in a cycle hub?
A ball bearing is used in a cycle hub to reduce friction between the moving parts of the wheel and the axle. The ball bearings allow the wheel to rotate smoothly with minimal resistance, enhancing the efficiency and longevity of the cycle.
Answer in detail.
Friction is a necessary evil – Explain.
Friction is called a necessary evil because it has both beneficial and detrimental effects.
Beneficial Effects:
Walking: We can walk without slipping due to the friction between our shoes and the ground.
Driving: Cars can move and stop safely because of the friction between tires and the road.
Holding Objects: We can hold and grip objects securely due to friction.
Detrimental Effects:
Wear and Tear: Friction causes wear and tear on moving parts of machines, leading to maintenance costs.
Energy Loss: A significant amount of energy is lost as heat due to friction in machines, reducing efficiency.
Noise and Heat: Friction generates unwanted noise and heat, which can be problematic in mechanical systems.
Give the different types of friction and explain each with an example.
Types of Friction:
Static Friction: The friction that acts on objects when they are at rest relative to each other. It must be overcome to start moving an object.
Example: Pushing a heavy box on the floor. The box does not move until the applied force exceeds the static friction.
Kinetic Friction: The friction that acts on objects when they are in motion relative to each other. It can be further divided into sliding and rolling friction.
Sliding Friction: Occurs when an object slides over another surface.
Example: Sliding a book across a table.
Rolling Friction: Occurs when an object rolls over a surface.
Example: Rolling a soccer ball on the ground. Rolling friction is usually less than sliding friction.
Explain how friction can be minimised.
Minimizing Friction:
Lubrication: Applying lubricants like oil or grease reduces the contact between surfaces, thus minimizing friction.
Ball Bearings: Using ball bearings reduces sliding friction by converting it to rolling friction, which is significantly lower.
Streamlining: Designing objects with smooth, streamlined shapes reduces air resistance, a form of friction.
Polishing Surfaces: Making surfaces smoother reduces friction by minimizing the microscopic irregularities.
