Download Technical Physics 1

Physics
Force
Force
• What is force?
– Any push or pull that tends to cause a change in
motion
– measured in Newtons (N) or pounds (lbs)
• 1 N = 0.225 lbs
– examples of force
•
•
•
•
gravity (weight)
magnetism
electricity
tension or compression
Newton’s Laws of
Motion
• 1st Law - Law of Inertia
– An objects motion will remain in motion until acted
upon by an outside force.
• 2nd Law - F = ma
– The net force on an object will cause it to accelerate
inversely proportional to its mass
• 3rd Law - Action - Reaction
– For every action there is an equal but opposite reaction
Equilibrium
• Forces are balanced (1st law)
• The net force (resultant force) is 0
• There is no change in motion
–a=0
– v is constant
Friction
• Friction (THEORY GIVEN BY GALILEO)is
dependant on 2 factors, the roughness of the
surfaces (coefficient of friction) in contact and the
force pushing the surfaces together (normal force)
Ffric = m Fnorm
Friction may be static (starting or kinetic (moving) You may
use subscripts to indicate this. ie. ms or mk
CONTACT FORCES
FRICTIONAL
TENSIONAL
NORMAL
AIR RESISTANCE
APPLIED
SPRING
AT A DISTANCE FORCE
GRAVITATIONAL
ELETRICAL
MAGNETIC
Normal force (Fnorm)
Applied(Fapp)
(Force on hanger)
Friction force (Ffric)
Gravity (Fgrav)
(Force on plane)
Force
x-component y-component
Applied
Fapp
0
Gravity
0
-W
Friction
-Ffric
0
Normal
0
N
Normal force (N)
Pull(P)
(Force on hanger)
Friction force (Ff)
Weight (W)
(Force on plane)
Free body diagrams are diagrams that
Show all the forces acting on an object
Wy =Wcos
Wx =Wsin
Force
x-component
y-component
Applied
P
0
Gravity
-Wsin
-Wcos
Friction
-Ff
0
Normal
0
N
P - Ff - Wsin = 0
N - Wcos = 0
F = 0
Wy =Wcos
Wx =Wsin
As long as the object is sitting still or at
constant acceleration
Fapp - Ffric - Wsin = 0
Fapp = Ffric + Wsin
Ff = m N
Fy = 0
Fx = 0
Fnorm - Wcos = 0
Fnorm = Wcos