Statics (the second half of the story)

Section 12.1, 12.3

1. Define torque 2 ways:

• t ≡ F x r
• A twisting action

 

2. Explain the difference between a vector dot product and cross product.

Note: the torque (t = F x r) and work (w = F•r) equations look like they'd yield the the result same but one is a cross product and a vector. The other is a dot product and a scalar

 

3. State all of the requirement for a static condition to exist.

SF_x = 0, SF_y = 0, SF_z = 0

St_xy =  0, St_yz =  0,  St_zx =  0

Note: We will typically work in only 2 dimensions (x, y) for forces and in only one plane (xy) for torque

 

Homefun: Problems 13, 15, 23, 57, 55. Serway

Metacognition Problem Solving Principle 6.1: When solving statics problems using torque equations the pivot point can be placed anywhere. Often the problem can be greatly simplified by placing it in a convenient location.

Lesson 1

Key Concept: Static equilibrium

Purpose: Define and understand the conditions required for static equilibrium.

Interactive Discussion: Objectives

In Class Problem Solving:  

1. Toto atop the storm cellar door
2. Luke Skywalker walks the plank.
3. Ed the restaurateur hangs his sign.
4. Bob's big bicept
5. Calculate mechanical advantage (what they didn't tell you in physical science class)