Basic Science Solutions for Class 8 Science Chapter 8 Force And Pressure are provided here with simple step-by-step explanations. These solutions for Force And Pressure are extremely popular among class 8 students for Science Force And Pressure Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Basic Science Book of class 8 Science Chapter 8 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Basic Science Solutions. All Basic Science Solutions for class 8 Science are prepared by experts and are 100% accurate.

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We have to apply force to change the speed or direction of the motion of a moving body.

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Force of friction brings the moving ball to rest in a while even is no force is applied.

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Gravitational force of earth causes the ball to fall back to the ground.

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Three types of force that can act from a distance are:
(a) Gravitational force
(b) Frictional force
(c) Magnetic force

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It is helpful to increase friction in stopping the tyres of moving vehicles and in the steering wheel of the car.

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Three disadvantages of friction between the parts of a machine are as follows:
(a) It causes surfaces to wear down.
(b) It produces heat.
(c) It wastes energy.

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Pressure is defined as the force applied per unit area of an object. The SI unit of pressure is N/m.

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The cutting edge of a knife is made sharp to decrease the surface area. This helps in applying more pressure.

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Atmospheric pressure causes a coaster placed over the rim of a glass of water to stick to the glass even when the glass is inverted.

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The SI unit of force is Newton (N).

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A streamlined body is defined as a body with smooth outlines. It is designed to reduce the resistance offered by air or water to its movement.

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(a) Oil reduces friction by filling up the dents on the surfaces that move against each other in a machine. It also prevents direct contact between the surfaces by forming a film between them.

(b) Ball bearing converts sliding friction into rolling friction, which is less than sliding friction. This helps in reducing friction.

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When a force is applied to move a body, frictional force resists the movement. As the force increases, the frictional force also increases. As the force applied becomes greater than the frictional force, the body starts moving and frictional force decreases. It is because frictional force has limited strength and as long as the force applied does not cross this limit, frictional force flexes its muscles and acts like a bully. When the force applied passes this limit, frictional force becomes weaker.

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(a) All these forces, i.e, magnetic, electrostatic and gravitational forces, can act from a distance.
(b) When a body leaves the earth's gravitational field, it becomes weightless.

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(a) Gravitational force depends on the mass of two bodies concerned. Moreover, unless one body is very massive, it cannot be felt. We all are almost equal in weight; therefore, we do not attract each other.

(b) Moon has considerably less mass than the earth itself. Therefore, force of gravity of moon is less than that of the earth.

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Spring balance measures the weight of a body.
Take a spring and hang it on a nail and note the length. Now, hang a small stone from the other end of the spring and note the increase in length. Hang a bigger stone and note the change in length of the spring again. It would be observed that the bigger the stone, greater is the extension of the spring, as a bigger stone has more mass. Therefore, it is pulled by the earth with a greater force. The extension of the spring gives the weight of the body. This is the principle on which a spring balance works.

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Pressure increases with the depth of a liquid. Let us prove it with the following example.
Take a U-tube and fix it on a board. Fill half of the tube with water such that both the arms of the tube have equal water level. This will work like a manometer. Now, attach one end of one meter rubber tube over one end of U-tube and attach funnel to the other end of the rubber tube. Stretch a thin balloon over the mouth of the funnel and fix it with thread or rubber band. Lower the funnel slowly into a bucket of water. The difference between the heights of water in the two arms of manometer will increase as the funnel goes deeper into the bucket of water. This shows that pressure increases with the depth of the liquid.   

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Friction helps us in cycling in the following ways:
1. It helps us in applying brakes.
2. It helps the cycle to move.
3. It keeps our feet on the pedals.
4. It helps us in gripping the handlebar.
5. It helps us to sit on the saddle.

Friction creates problems while cycling in the following ways
1. Friction between moving parts wastes energy.
2. Friction causes wearing down.
3. Air resistance wastes our energy.

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1. Rolling friction is less then the sliding friction.
2. A body has weight because of gravitational force.
3. The force which opposes the motion of one body over another is frictional force.
4. The smoother the surface, the lesser is the frictional force.
5. Kinetic friction is less than the static friction.
6. The smaller the area over which a force is applied, the higher is the pressure.
7. The pressure at a particular depth in a liquid is same in every direction.

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(c) between all bodies in the universe
Gravitational force acts between all bodies in the universe because it is a universal force.



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(c) 1 kgf = 9.8 N
The relation between the SI units of force and weight of a one kilogram mass is given by the formula:
 1 kgf = 9.8 N

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(b) 10 N/m2
If a force of 100 N acts on an area of 10 m2, the pressure equals 10 N/m2 because:
    Pressure = Force/Area

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(d) water reduces friction between the road and the tyres
A car skids on a wet road because water reduces the friction between the road and the tyres.

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(c) Friction helps a ship move through water
There is no friction between a ship moving through water.

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1. Gravitational force  A. Contact force m. Makes a pencil work
B, t, n B. Non-contact force n. Acts between any two objects
2. Frictional force   o. Always opposes motion
A, o, s   p. Can act on iron but not on paper
3. Magnetic force   q. Can act on paper
B, p   r. A non-contact force that depends on mass
4. Electrostatic force   s. Reduces when a body starts moving
B, q   t. Prevents objects from flying away from earth



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