Mechanics · Forces & Newton's laws
Chapter 1 · 3
The idea
Connected particles
Why two bodies joined by a light inextensible string share one acceleration and one tension, the two-step method that runs every problem — whole system for the acceleration, a single body for the internal force — and why the connecting force is internal to the system but external to each body.
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
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Mechanics · Forces & Newton's laws
Connected particles
Why two bodies joined by a light inextensible string share one acceleration and one tension, the two-step method that runs every problem — whole system for the acceleration, a single body for the internal force — and why the connecting force is internal to the system but external to each body.
Why it works
Two facts unlock everything
Tow a trailer, stack two blocks, hang a load from a lift: in each case two bodies move together, joined by a string or by contact.- Same acceleration. A light, inextensible string can't stretch, so the two bodies move as one rigid unit — they have the same acceleration. (Bodies simply in contact and staying in contact share an acceleration too.)
- Same tension. A light string has no mass, so the tension is the same all the way along it — the trailer pulls back on the car exactly as hard as the car pulls forward on the trailer. There is one number , not two.
Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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