Example: Ladder Leaning Against a Wall
Given: A ladder leans against a frictionless wall.
Required: Angle between ladder and ground when it
starts to slip.
EF 152 Spring, 2015 Lecture 1-3
What is the sign of the moment of Nw about the base
of the ladder?
What is the equation for the magnitude of the
moment caused by Nw about the base of the ladder?
2
Stability
Tipping calculations:
• Be careful with the ‘normal force’ location
• Assume normal force location at point at
which the object _________
Tipping with arbitrary loads:
•
Sum moments about each extreme and assume the normal
force to be located at that point
•
If the resultant moment would cause the object to fall away
from the support area, then the object will tip
•
Also need to consider ______________.
Which of the five scenarios is impossible?
EF 152 Spring, 2015 Lecture 1-3
4
Example: Stability
A truck is parked on an inclined road
as shown. Determine the slope of the
road that causes the truck to tip over.
1.6 m
Center of mass
2.4 m
θ
2.2 m
EF 152 Spring, 2015 Lecture 1-3
5
Example: Refrigerator
A 200 pound refrigerator is on an incline.
Determine the range of the force P so
the refrigerator does not move.
P
µs=0.6
40°
EF 152 Spring, 2015 Lecture 1-3
N=?
Minimum tipping force
6