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Question Number 22071 by Tinkutara last updated on 10/Oct/17

STATEMENT-1 : If an object is at  rest then there should not be any friction  on it.  STATEMENT-2 : If an object is moving  then the friction acting on it has to be  kinetic.  STATEMENT-3 : If an object is at rest  then kinetic friction cannot act on it.

$$\mathrm{STATEMENT}-\mathrm{1}\::\:\mathrm{If}\:\mathrm{an}\:\mathrm{object}\:\mathrm{is}\:\mathrm{at} \\ $$$$\mathrm{rest}\:\mathrm{then}\:\mathrm{there}\:\mathrm{should}\:\mathrm{not}\:\mathrm{be}\:\mathrm{any}\:\mathrm{friction} \\ $$$$\mathrm{on}\:\mathrm{it}. \\ $$$$\mathrm{STATEMENT}-\mathrm{2}\::\:\mathrm{If}\:\mathrm{an}\:\mathrm{object}\:\mathrm{is}\:\mathrm{moving} \\ $$$$\mathrm{then}\:\mathrm{the}\:\mathrm{friction}\:\mathrm{acting}\:\mathrm{on}\:\mathrm{it}\:\mathrm{has}\:\mathrm{to}\:\mathrm{be} \\ $$$$\mathrm{kinetic}. \\ $$$$\mathrm{STATEMENT}-\mathrm{3}\::\:\mathrm{If}\:\mathrm{an}\:\mathrm{object}\:\mathrm{is}\:\mathrm{at}\:\mathrm{rest} \\ $$$$\mathrm{then}\:\mathrm{kinetic}\:\mathrm{friction}\:\mathrm{cannot}\:\mathrm{act}\:\mathrm{on}\:\mathrm{it}. \\ $$

Commented by ajfour last updated on 10/Oct/17

 a block not slipping and resting  on a rough inclined plane , then  friction is in action.    a wheel  rolling without sliding  on a rough plain horizontal floor,  no friction  acts.    other forces keep a the object  at rest while some other object  slides over it.

$$\:{a}\:{block}\:{not}\:{slipping}\:{and}\:{resting} \\ $$$${on}\:{a}\:{rough}\:{inclined}\:{plane}\:,\:{then} \\ $$$${friction}\:{is}\:{in}\:{action}. \\ $$$$ \\ $$$${a}\:{wheel}\:\:{rolling}\:{without}\:{sliding} \\ $$$${on}\:{a}\:{rough}\:{plain}\:{horizontal}\:{floor}, \\ $$$${no}\:{friction}\:\:{acts}. \\ $$$$ \\ $$$${other}\:{forces}\:{keep}\:{a}\:{the}\:{object} \\ $$$${at}\:{rest}\:{while}\:{some}\:{other}\:{object} \\ $$$${slides}\:{over}\:{it}.\: \\ $$

Commented by Tinkutara last updated on 11/Oct/17

3^(rd)  is not clear. Why kinetic friction  will act on it then?

$$\mathrm{3}^{\mathrm{rd}} \:\mathrm{is}\:\mathrm{not}\:\mathrm{clear}.\:\mathrm{Why}\:\mathrm{kinetic}\:\mathrm{friction} \\ $$$$\mathrm{will}\:\mathrm{act}\:\mathrm{on}\:\mathrm{it}\:\mathrm{then}? \\ $$

Commented by ajfour last updated on 11/Oct/17

say a light block slides on the   inclined surface of a heavy  wedge, the wedge remains at  rest but there is kinetic friction  between block and wedge which  the wedge expeeiences and it is  at rest due to static friction on  ground.

$${say}\:{a}\:{light}\:{block}\:{slides}\:{on}\:{the}\: \\ $$$${inclined}\:{surface}\:{of}\:{a}\:{heavy} \\ $$$${wedge},\:{the}\:{wedge}\:{remains}\:{at} \\ $$$${rest}\:{but}\:{there}\:{is}\:{kinetic}\:{friction} \\ $$$${between}\:{block}\:{and}\:{wedge}\:{which} \\ $$$${the}\:{wedge}\:{expeeiences}\:{and}\:{it}\:{is} \\ $$$${at}\:{rest}\:{due}\:{to}\:{static}\:{friction}\:{on} \\ $$$${ground}. \\ $$

Commented by Tinkutara last updated on 11/Oct/17

Thank you very much Sir!

$$\mathrm{Thank}\:\mathrm{you}\:\mathrm{very}\:\mathrm{much}\:\mathrm{Sir}! \\ $$

Answered by ajfour last updated on 10/Oct/17

1−not always true  2−not always true  3−not always true

$$\mathrm{1}−{not}\:{always}\:{true} \\ $$$$\mathrm{2}−{not}\:{always}\:{true} \\ $$$$\mathrm{3}−{not}\:{always}\:{true} \\ $$

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