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.

68.2 problems involving dry friction

example 8.1

78.2 problems involving dry friction

example 8.1

88.2 problems involving dry friction

example 8.3

98.2 problems involving dry friction

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

139.2 composite bodies

example 9.10

149.2 composite bodies

example 9.10

159.2 composite bodies

example 9.11

169.2 composite bodies

example 9.11