e14 - applied mechanics: statics

1mon/wed/fri, 12:50-2:05pm, 370-370

e14 - applied mechanics: statics

2syllabus

e14 - applied mechanics: statics

fifthhomework

due

38.1 characteristics of dry friction

• the heat generated by theabrasive action of friction canbe noticed when using thisdrinder to sharpen a metalblade• friction is a force thatrisists the movement of twocontacting surfaces relativeto one another• friction always acts tan-gent to the surface and is di-rected opposite to a possiblemotion

from friction to heat

4

theory of dry friction

8.1 characteristics of dry friction

8.2 problems involving dry friction

slipping & tipping

pushing on the uniform crate of weight W sitting on a rough surface. if themagnitude P is small, the crate will remain in equilibrium and not move(left FBD). as P increases, the crate will either be on the verge of slipping,F = µs · M, or, if the surface is very rough with large µs, the resultant forcemoves towards the corner and beyond, x>b/2, and the crate will tip over.tipping also depends on the height h of the force P.


example 8.1


example 8.1


example 8.3


example 8.3

109. center of gravity and centroid

• to discuss the concept of thecenter of gravity, center ofmass, and centroid• to show how to determinethe center of gravity and cen-troid for a system of par-ticles• to show how to determinethe center of gravity and cen-troid for composite bodies

today‘s objectives

119.1 center of gravity/mass and centroid

location of the center of gravity from sum of all forces andmoments of resultant

center of a collection of particles

x = ! x dW ! dW

y = ! y dW ! dW

z = ! z dW ! dW

129.2 composite bodies

the center of gravity of thiswater tank can be determinedby dividing it into compositeparts

divide the structure!

x = ! x W ! W

y = ! y W ! W

z = ! z W ! W

I

II

III


example 9.10


example 9.10


example 9.11


example 9.11

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e14 - applied mechanics: statics