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# Pulleys watch

1. http://i-want-to-study-engineering.o...nt_of_inertia/
why are the tensions different?
in the following video, it is the same:
http://www.examsolutions.net/maths-r...tutorial-1.php
2. (Original post by runny4)
http://i-want-to-study-engineering.o...nt_of_inertia/
why are the tensions different?
in the following video, it is the same:
http://www.examsolutions.net/maths-r...tutorial-1.php
In the first one it's not a "light" pulley, so you need the difference in the tensions to get the pulley turning. In the early mechanics modules in A level Maths, the pulleys are always light.
3. (Original post by tiny hobbit)
In the first one it's not a "light" pulley, so you need the difference in the tensions to get the pulley turning. In the early mechanics modules in A level Maths, the pulleys are always light.
ok thanks
4. Take a look at the first couple of pages in the Edexcel M1 book. A pulley is considered to be smooth (no friction at the pulley), with its strings light (the strings have no weight) and inextensible (the strings have equal acceleration, i.e. equal force).
5. (Original post by aymanzayedmannan)
Take a look at the first couple of pages in the Edexcel M1 book. A pulley is considered to be smooth (no friction at the pulley), with its strings light (the strings have no weight) and inextensible (the strings have equal acceleration, i.e. equal force).
And the pulley is light, so that the tension can be the same on both sides.

Equal acceleration does not, of itself, mean that the tensions must be the same.

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