Page 67 - Innovator's Science-8

Grasp-Up

Force: A push or pull that can change the state of mo on or shape of an object.
Mo on: The act of moving or changing posi on.
Contact force: A force that occurs only when two objects are in physical contact.
Non-contact force: A force that acts even when objects are not touching each other.
Muscular force: The force produced by the muscles of animals, including humans.
Fric on: A force that opposes mo on between two surfaces in contact.
Buoyant force: The upward force exerted by a liquid on an object immersed in it.
Upthrust: Another name for buoyant force; the upward push of a fluid.
Balanced forces: Forces that cancel each other's effect and keep an object at rest or moving uniformly.
Unbalanced forces: Forces that do not cancel each other's effect and cause mo on or a change in speed.
Fluid pressure: The pressure exerted by liquids or gases in all direc ons.
Atmospheric pressure: The pressure exerted by the air around us due to its weight.
Hydraulic system: A system that uses liquid pressure to transmit force and perform work.
Spring balance: An instrument used to measure the weight of an object using the extension of a spring.

Points to Reflect

• Force is seen as a push or a pull.
• Force acts only when the objects interact.
• Pressure is exerted by solids, liquids and gases.
• Atmospheric pressure is measured using a barometer.
• Friction is offered by one object or the other only when they are in contact.
• Friction wastes energy, wears out the rubbing surfaces and generates heat.
• Static friction is greater than sliding friction which is greater than rolling friction.

NCERT Textbook Questions (Solved)

Let Us Enhance Our Learning

1. Why does it feel harder to pedal a bicycle when going uphill than on flat ground?
Ans. When we ride a bicycle uphill, gravity tries to pull us back down toward the ground. On flat land, gravity
only pulls straight down, so it doesn’t make it harder to move forward. But on a slope, part of gravity
pulls backward against us, so we have to push harder to keep moving up the hill.
2. Why is it easier to slip on a wet surface?

Ans. It is easier to slip on a wet surface because the fric on between your foot and the ground becomes less.
The water forms a thin layer that acts like a lubricant, reducing grip and making it easier to slide.

3. Why do we feel ‘light’ or like we are ‘floa ng’ just a er our swing reaches its highest point and begins
to come down?
Ans. Do yourself

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Science-8