Transcript statics FBD2010

Physics Day 42 – FBD
-LO: FBD with numbers
-LO: FBD for Static problems
AGENDA
Do Now
Finish WS1
Notes
Do Now –
1. Please draw a Free
Body Diagram of a 5kg
book lying on a table
being pulled by a string
to the right with a force
of 3N. (not moving)
What is force do?
• How do we change motion in velocity or only
direction? Why some objects accelerate at
higher rates than others do?
• A force is a push or pull upon an object resulting
from the object's interaction with another object.
Whenever there is an interaction between two
objects, there is a force upon each of the
objects.
• Forces cause changes in velocity over time, or
accelerations.
Type of forces
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Contact Forces
Frictional Force
Tension Force
Normal Force
Air Resistance Force
Applied Force
Spring Force
Type of forces
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Action-at-a-Distance Forces
Gravitational Force
Electrical Force
Magnetic Force
Normal Forces
Physics Book
Table
Normal Forces
a=0
Physics Book
Table
Fn
Fg
Friction
The force of friction is zero because the book is not trying to
slide in any direction. If you put a friction force in, it would
be unbalanced and cause an acceleration (and that never
happens)
a = 0, v = 0
Physics Book
Table
Fn
Fg
Friction
String tied to book
Physics Book
Table
Friction
String tied to book
Fstring
Physics Book
Table
Fµ
Fn
Fg
a = 0 (constant velocity to the right)
Equilibrium and Statics
When all the forces that act upon an object
are balanced, then the object is said to be
in a state of equilibrium.
The forces are considered to be balanced
if the rightward forces are balanced by the
leftward forces and the upward forces are
balanced by the downward forces.
Determining the Net Force
• An object at rest tends to stay at rest and
an object in motion tends to stay in motion
with the same speed and in the same
direction unless acted upon by an
unbalanced force.
Spring Forces
• Stretched spring Fs< 0
• Equilibrium Fs=0
4.00 kg
The object hung from the cable has a weight of 25 N. Write the equation for the
sum of the forces in the y-direction. What is the tension in the cable? Repeat the
problem above with a 5 degree angle. How does the tension compare?
The object hung from the cable has a weight of 25 N. Write the equation for the
sum of the forces in the y-direction. What is the tension in the cable? Repeat the
problem above with a 5 degree angle. How does the tension compare?
2TSin30 = 25N
T=25N
T2Cos30 = 30N
T2Sin30 = T1
T2 = 2*T1
T2 = 30N/0.87
T2 = 34.5N
T1 = 69N
Use g = 10 m/s/s
W=mg = 20 kg * 10 m/s/s = 200N
Fn = mgCos30 = 200N*cos30 = 174N
How did we do that?