1. Engineering Mechanics Lecture 2
5/10, Friday
3-4am

2. 2-Particle Interactions
Sun : earth
f21
Atom : atom
f12 2 1

3. 3-Particle InteractionsF3 3
f32
f23
f31 2 F2
f13
f21 F1
f12 1

4. Many-Particle Interactions
For an N particles system, in equilibrium
Newton’s 1st law F3 3
Summation of the above equation gives
f32
f23
f31 2 F2
f13
Newton’s 3rd law
f21 F1
f12 1
Therefore:

5. Free-Body-Diagram
Isolate the body in question with the representation of all external forces acting on it.

6. Problem 1

7. Remove Spike from Timber
It is desired to remove the spike from the timber by applying force along its horizontal axis. An obstruction A prevents direct access, so that two forces, one is 1.6kN and the other P, are applied by cables as shown. Compute the magnitude of P necessary to ensure axial tension T along the spike. Also find T.

8. Remove Spike from Timber
Vertical:
Horizontal:

9. Problem 2

10. Knot in Static Equilibrium?F1 F2
Horizontal: a b
Vertical:
Mass: m

11. When strings are almost straight horizontallyF1 F2 a b
when
Mass: m