direction and point of application.

Transcription

1 Konu 1 DEINITION ND CLSSIICTION O ORCES s dened beoe, oce s an acton o one bod on anothe. It s a ecto quantt snce ts eect depends on the P decton as well as on the magntude o the acton. The eect o the oce appled to the bacet depends on P, the angle and the locaton o the pont o applcaton. Changng an one o these thee speccatons wll alte the eect on the bacet such as the ntenal oce geneated n the wall o deomaton o the bacet mateal at an pont. Thus, the complete speccaton o the acton o a oce must nclude ts magntude, decton and pont o applcaton. We can sepaate the acton o a oce on a bod nto two eects as etenal and ntenal. o the bacet, the eects o P etenal to the bacet ae the eacte oces (not shown) eeted on the bacet b the wall. oces etenal to a bod can be ethe appled o eacte oces. The eect o P ntenal to the bacet s the esultng ntenal oces and deomatons dstbuted thoughout the mateal o the bacet. oces ae classed as ethe contact o bod oces. contact oce s poduced b dect phscal contact; an eample s the oce eeted on a bod b a suppotng suace. bod oce s geneated when a bod s located wthn a oce eld such as a gatatonal, electc o magnetc eld. n eample o a bod oce s ou weght. oces ma be uthe classed as concentated o dstbuted.

2 Konu Ee contact oce s actuall appled oe a nte aea and s theeoe a dstbuted oce. Howee, when the dmensons o the aea ae e small compaed wth the othe dmensons o the bod, the oce ma be consdeed concentated at a pont. oce can be dstbuted oe an aea, as n the case o mechancal contact, oe a olume when a bod oce such as weght s actng o oe a lne, as n the case o the weght o a suspended cable. Concentated oce concete Dstbuted oce The weght o a bod s the oce o gatatonal attacton dstbuted oe ts olume and ma be taen as a concentated oce actng though the cente o gat. cton and Reacton ccodng to Newton s thd law, the acton o a oce s alwas accompaned b an equal and opposte eacton. It s essental to dstngush between the acton and the eacton n a pa o oces. To do so, we st solate the bod n queston and then dent the oce eeted on that bod (not the oce eeted b the bod). It s e eas to mstaenl use the wong oce o the pa unless we dstngush caeull between acton and eacton.

3 Konu 3 CLSSIICTION O ORCES CCORDING TO THEIR WYS O PPLICTION: Concuent oces Coplana oces Paallel oces Collnea oces The elatonshp between a oce and ts ecto components must not be conused wth the elatonshp between a oce and ts pependcula (othogonal) poectons onto the same aes. o eample, the pependcula poectons o oce onto aes a and b ae a and b, whch ae paallel to the ecto components o 1 and. It s seen that the components o a ecto ae not necessal equal to the poectons o the ecto onto the same aes. The components and poectons o ae equal onl when the aes a and b ae pependcula. b b 1 a a

4 Konu 4 SOME COMMON TYPES O ORCES CONTCT ND RICTION ORCE Let s consde two bodes whch ae n contact. The oce actng on bod 1 om bod s. can be dded nto two components as a nomal oce N, dawn pependcula to the tangent lne at the pont o contact and oce, dawn paallel to the tangent lne. N s named as the nomal component o the contact oce and s named as the cton component o the contact oce. I the contactng suaces ae smooth, then can be neglected ( 0); but the contactng suaces ae ough t has to be taen nto consdeaton. The elatonshp between N and s gen b µn, whee µ s a dmensonless coecent o cton ang between 0 and 1. tangent N N tangent N tangent N

5 Konu 5 N ORCES IN STRINGS, CLES, WIRES, ROPES, CHINS ND ELTS oces n stngs, cables, etc. ae alwas taen along the stng, cable, etc. and the decton alwas ponts awa om T the bod n consdeaton. The eet oce onl when the ae tght. When loose the eet no oce. Hence, the alwas wo n tenson. Usuall the weghts ae neglected compaed to the oces the ca o suppot. ORCES IN PULLEY ELT SYSTEMS Pulles ae wheels wth gooes that ae used to change the dectons o belts o opes and T 1 geneate a hghe output load wth a much smalle nput oce. Unless stated othewse, o appaent T 1 T T om the poblem, the tenson oces at both sdes o a belt ae taen as equal. The ae equal as long as the belt does not slde on the pulle, and the pulle otates eel wth a constant eloct.

6 Konu 6 ORCES IN SPRINGS spng (Spng oce) (: spng constant, : deomaton o the spng) spng Spng oce s alwas dected along the spng and s n the decton as to etun the spng nto ts undeomed length. (a) (b) 1 P P 1 Unstetched poston Stetched poston Uncompessed poston Compessed poston

7 Konu 7 THREE DIMENSIONL DESCRIPTION O ORCE * When the decton angles o a oce s gen; The angles, the lne o acton o a oce maes wth the, and aes ae named as decton angles. The nes o these angles ae called decton nes; the spec the lne o acton o a ecto wth espect to coodnate aes. In ths case, decton angles ae, and. Decton nes ae, and. l m n * When coodnates o two ponts along the lne o acton o a oce s gen; n m l e e ) (,, 1 1 n m l e, ( ) ( ) ( ) ( ) ( ) ( ) / / e (,, ) (,, ) / e

8 Konu 8 * When two angles descbng the lne o acton o a oce gen; e sn sn sn sn sn ( sn sn ) e ( sn sn )