Phy21 - Chap 5: Turning effects of forces (incomplete)

Moment/ torque

quantitative measure of the tendency of a force to cause rotational motion around a pivot (eg opening a door, opening a can)
Moment = F x perpendicular distance (d) from pivot to line of action

Principal of moments states that ____.

for any object in rotational equillibrium, the sum of CM about any point (acting as a pivot) is equal to the sum of ACM about the same point.
Basically, sum of CM = sum of ACM

CG of an object

point through which the entire weight of an object appears to act for any orientation of the object.

What is a couple?

Pair of forces that are
1. equal in magnitude
2. opposite in direction
3. lines of action do not coincide

Static equilibrium

Translational equilibrium (FR = 0) and rotational equilibrium (TR aka torque = 0)

Types of equilibria (3)

1. Stable: low CG + wide base. When slightly displaced, will return to OG position
2. Unstable: high CG + narrow bade. When slightly displaced, will fall away from OG position
3. Neutral equilibrium: CG remains at same level. When slightly displaced, will stay in equilibrium in new position

Stability of an object

ability of an object to regain its OG position after being tilted

Factors affecting stability

1. Base area (affect line of action)
2. Height of CG (allows inc degrees of tilts, can dec height of CG by increase weight at bottom)

Maximum angle of tilt

angle when the object just begins to topple