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✦ Class 8 · Science
Exploring Forces
You'll learn why a giant ship floats, but a tiny nail sinks, and how you can make paper bits dance without touching them!
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What this lesson covers
Step by step, in this order.
- 1Define force as a push or pull from an interaction between two objects. State its SI unit: Newton (N).
- 2Explain the effects of force: sets a still object moving (kicking a football), changes speed (bicycle brakes), changes direction (catching a cricket ball), and changes shape (squeezing a sponge).
- 3Introduce the comparison table with two columns: 'Contact Forces' (objects touching) and 'Non-Contact Forces' (objects not touching).
- 4Introduce Muscular Force (e.g., pushing a trolley) and Friction (e.g., rolling a ball on carpet vs tiles, bicycle brakes, slipping on a wet floor). Explain friction is more on rough surfaces and less on smooth or wet ones, and can be increased or reduced when useful.
- 5Introduce Magnetic Force (e.g., magnets attracting/repelling) and Electrostatic Force (e.g., rubbed objects; like charges repel, unlike attract).
- 6TRY IT activity: Rub a balloon on your dry hair, then bring it near small bits of paper. Observe what happens due to electrostatic force.
- 7Introduce Gravitational Force (e.g., Earth pulling things down, an astronaut on the Moon).
- 8Explain Mass vs Weight: Mass is the amount of matter (kg) and is the same everywhere. Weight is the gravitational pull on it (N) and changes with place. We measure weight with a spring balance.
- 9NUMERICAL: Work through an example: Weight = mass x 10 N per kg (on Earth). A 60 kg bag weighs 600 N. On the Moon, its weight is about one-sixth, so 100 N, but its mass is still 60 kg.
- 10Explain Floating and Sinking: Water pushes up with a 'buoyant force' or 'upthrust'. An object floats when the upthrust can balance its weight.
How it looks
A real board, not a video.
This board is from a different Science lesson — yours will look like this. She writes and draws while she explains, and stops to check you followed.
Doubts this lesson clears up
- Why is friction sometimes helpful and sometimes a problem we try to reduce?
- How can forces like magnetism or gravity work without objects actually touching each other?
- If my weight changes on the Moon, why does my mass stay the same?
- How can a giant, heavy ship float, but a tiny, light nail sinks?
- What happens if the buoyant force pushing an object up is less than its weight?
- Can we always feel or see the forces acting on objects?
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