Do It Now . Newton’s Laws Quiz. 1011 or 1012: Physics. Notes on Free Body diagrams Practice with Free Body diagrams Force calculations Homework : Finish free body diagrams and Freaky Forces; QUIZ next class. Proficiencies.
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Freebody
Speeding up
+
Sum of all the F
∑F = Fnet

Slowing down
0
At rest
Constant speed
Reaction to weight
perpendicular
Usually = weight
weight
Unless freefall
Let’s calculate your mass now:
Pounds/2.2 lb/kg = ?
downward
Or an inclined plane
Depends on location
X 26.8 m/s/s
In space, weight = 0
Mass is NOT = 0
X 9.81 m/s/s
X 2.7 m/s/s
Only overcome Ffriction
acceleration
Gravity does not slow objects moving horizontally. ONLY friction does
To move an object
If Fnet not = 0
Fnormal = Wt
Fnet = ?
F= ma=( 9.81 m/s/s)(25 kg)
Since the box is moving at a CONSTANT speed, the Fapplied = Ffriction.
Fnormal = Wt
Fnet vertical = ?
FFriction = 12.5N
F= ma =( 9.81 m/s/s)(5 kg)
Fnet horizontal = ?
Since the box is accelerating, the
Fnet = Fapplied  Ffriction.
Fnormal = Wt
Fnet vertical = ?
FFriction = 23.5N
F = ma =( 9.81 m/s/s)(7.2 kg)
Fnet horizontal = ma = (7.2 kg)(6.5 m/s/s) = ?
46.8N = Fapplied – 23.5N. What is Fapplied?
The force that produces equilibrium is equal in magnitude and opposite in direction.
Why is the red arrow longer than the blue ones this time?
Why isn’t the red arrow directly opposite in direction?
What is the resultant force?
8N
8N + 6N = 14 N north
6N
What force would put this in equilibrium?
14 N due south
7N + 5N = 12 N north
Plus some components outward
What is the resultant force?
The N part drops to say 5N
The N part drops to say 7N because some of it is outward now
What force would put this in equilibrium?
12 N due south and some components inward
5N + 3N = 8 N north
Plus more components outward
What is the resultant force?
The N part drops to say 3N
The N part drops to say 5N because some of it is outward now
What force would put this in equilibrium?
8 N due south and morecomponents inward
8N  6N = 2 N blue direction
What is the resultant force?
What force would put this in equilibrium?
2 N due red direction
This vector has one component because we choose to set it at the 0 deg position.
Could it possibly be in equilibrium now?
What direction would the spring scales move?
25 N
19 N
The vector or force that would put it in equilibrium would also have a left and a down vector component.
? N
This vector has a to the right component and a down component (as we look at it)
25 N
19 N
? N
If the mass of the elevator is 435 kg, what is the tension in the rope?
Would this increase or decrease if the elevator accelerated upward?
If it accelerated downward?
Tension = weight
Weight = Fup