Class 8 Science Force

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Fill in the blanks :

1.—–Force-——– is a push or pull acting on an object.

1. Magnetic and gravitational forces are the types of—–non-contact ——- force.
2. The S.I. unit of pressure is—— N/m2 or Pa ———–

.

1. It is easier to carry school bags with ——- broad ———straps.
2. Foundations of high-rise buildings are kept——– wide foundations ———–.
3. Iron nails can be separated from husk by using—–magnet——-.

State whether True or False

1. The pressure in a liquid at greater depths is greater. T
2. A piece of rubber regains its shape on squeezing. T
3. Cutting and piercing tools have blunt edges. F
4. Camel cannot walk on sand due to its broad feet. F
5. Non-contact force can act from a distance. T
6. The syringe works on a principle of atmospheric pressure. T
7. People at plains suffer from nose bleeding. F
8. Fluids exert pressure. T

Give reasons for the following:

1. School bags have broad straps.

Larges area of cross-section of school bag reduces the pressure

1. A camel can easily walk on sand.

This is due to the fact that nature has provided the camel with broad feet. Hence, when a camel walks on sand, the pressure exerted by it on the sand is quite small due to the increased area of contact, its feet do not sink much in the sand. Therefore, a camel can easily cross vast regions in deserts.

1. Some people suffer from nose bleeding at high altitudes.

The atmospheric pressure is a maximum on the surface of the earth. When we go to a higher altitude (say a high mountain), then the atmospheric pressure decreases. So, at high altitudes, the atmospheric pressure becomes much less than our blood pressure. Since our blood is at a higher pressure than the outside pressure,

Therefore, some of the blood vessels in our body burst and nose bleeding can occur at high altitudes.

1. Astronauts wear special suits in space.

Spacesuits help astronauts in several ways. Spacewalking astronauts face a wide variety of temperatures. In Earth orbit, conditions can be as cold as minus 250 degrees Fahrenheit. In the sunlight, they can be as hot as 250 degrees. A spacesuit protects astronauts from those extreme temperatures.

Spacesuits also supply astronauts with oxygen to breathe while they are in the vacuum of space. They contain water to drink during spacewalks. They protect astronauts from being injured from impacts of small bits of space dust.

1. An apple always falls to the ground from the tree.

The earth pulls them down due to the force of gravity or gravitational force.

1. A heavy truck is fitted with six to eight wheels.

A heavy truck is fitted with six to eight wheels because increased area reduces the pressure on wheels so they do not burst or damage on the road. the truck has broad tyres so that there is less pressure on the ground and the tyres do not sink in the soil.

1. Skiers use long flat skies to slide over snow.

Skiers use long and flat skies to slide on the snow. Larges area of the cross-section of skies reduces the pressure on the snow and prevents the skiers from sinking into the soft ground. So, the skiers

easily slide over snow without sinking their feet into the ground.