Lecture 3 Differential geometry of surfaces 3.1 Definition of surfaces Implicit surfaces F(r,,a)=0 Example: 22+6+2=1 Ellipsoid, see Figure 3.1 Figure 3.1: Ellipsoid · Explicit surfaces If the implicit equation F(, y, a)=0 can be solved for one of the variables as a function
I. Choose the Correct Answer 1. Which of the following quantities are independent of the choice of inertial frame? (There may be more than one correct answer) (A)Velocity (B)Acceleration (C)Force (D)Work Solution: In all the inertial frame, the forces acted on a body are same,=ma=F'=ma', therefore the force and acceleration are independent of the choice of inertial frame
Before we look specifically at thin-walled sections, let us consider the general case (i.e, thick-Walled) Hollow thick-walled sections Figure 12.1 Representation of a general thick-walled cross-section 中=c2 on one boundary φ=c1 on one boundary This has more than one boundary(multiply-connected do=0 on each boundary
1. abide by(=be faithful to;obey)忠于;遵守。 2. be absent from缺席,不在 3. absence or mind(=being absent-minded-)心不在焉 4. absorb(=take up the attention of)吸…的注意力(被动语态):be