Surface area
• The different size of surface
area does not create different
friction force of an object
(_____)
• Why? Î ________
↑Area, ↓Pressure
↓Area, ↑Pressure
• Pressure : P = F/A
Unit : 1.0 Pascal (Pa) = 1.0 N/ 1
Cf) 1 psi = 6894.8 Pa
a and friction
t
1.0m2
Friction in spo
move
• Friction is good or bad in spo
• Following action will increas
coefficients?
– The grips of racket or bat
leather or rubber ( )
– The soles of the balling s
friction coefficient
– Waxing the bottom of sno
– Touching rosin bag prior
– Spike of the sole of runni
– What about chalks of gym
ort and human
ement
ort and human movement?
se friction or decrease friction
t are made of materials such as
shoes are designed to ( )
ow skis ( ) )
to pitching ( )
ing shoe ( )
mnast’s hand? (
Addition
• Vector Addition
– “tip-to-tail” method
– Component (decompo
• Colinear forces vs Co
of forces
osition) method
oncurrent forces
Static Equ
• In case of ΣF = 0, there
• Newton’s 1st law
• Two case for static equ
– Stationary (No moving)
– Constant velocity
• How to solve problems
1. Draw FBD
2. Define appropriate coor
3. Establish ΣF = 0 for eac
4. Solve the unknowns
uilibrium
e is static equilibrium
uilibrium
)
s of static equilibrium
rdinate system
ch axis
Example)
Example)
F
W
Fs RN
Example ) Static friction coeffic
θ
cient (µs)
Q4 (chap 4) Dave is trying to pu
field. Dave pulls on the rope atta
upward and forward force of 300
are directed at an angle of 30° ab
is 50 kg, and the sled’s mass is 8
friction between the sled runners
Dave move the sled?
ull Dana on a sled across a flat
ached to the sled with an
0 N. This force and the rope
bove horizontal. Dana’s mass
8 kg. If the coefficient of static
s and the snow is 0.10, will
A 60-kg skier is in a tuck and mov
resistance pushes backward on the
force acts in a direction upward an
coefficient of dynamic friction bet
0.08. What is the resultant force th
ving straight down a 30° slop. Air
e skier with a force of 10 N (this
nd parallel to the 30° slope). The
tween the skis and the snow is
hat acts on the skier?
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Terminal Velocity • The object’s velocity when the acceleration of falling become _____. • Air resistance (Aerodynamic drag) f(drag coefficient, surface
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