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课程 7 · 年级 6–8
Forces: Newton and three laws
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Newton described motion in three rules. 1) A body at rest stays at rest until a force pushes (inertia — that is why braking throws you forward). 2) F = m×a: force equals mass times acceleration — heavy things are harder to speed up. 3) Action = reaction: the rocket pushes gas down — the gas pushes the rocket up.
- ●Mass (kg) ≠ weight (N): less weight on the Moon, same mass
- ●Friction: helps walking, slows machines
- ●Aerodynamics: shape decides, the sports car "cuts" air
🚗 The seatbelt is inertia\u2019s direct consequence: on impact the body keeps flying at vehicle speed. Always buckle up.