Specifications

K
K56
Parker Hannifin Corporation
Pneumatic Division
Wadsworth, Ohio
www.parker.com/pneumatics
Pneumatic Actuator Products
Air Motors
Frictional Forces Between Two Objects
A frictional force always occurs between two objects with
surfaces in contact with each other. It is always exerted against
the direction of movement.
The frictional force is either static or kinetic. When selecting
an air motor, we need to consider the larger of the two forces,
static or kinetic.
The size of the static frictional force or the kinetic frictional
force is the product of the normal force F
n and the coefficient
of static friction (µ
0
), or the product of the normal force Fn and
the coefficient of kinetic friction (µ).
The size of the contact surface between the objects is
irrelevant.
Formula:
F
static
= Fn x µ
0
F
kinetic
= Fn x µ
F
n
= m x g
F
static
= static friction in N
F
kinetic
= kinetic friction in N
F
n
= force from object in N
m = mass in kg
g = gravitation (9.81) in m/s
2
Material Coefficient of Static Friction µ
0
Dry Lubricated
Bronze Bronze 0.28 0.11
Bronze Grey Iron 0.28 0.16
Grey Iron Grey Iron — 0.16
Steel Bronze 0.27 0.11
Steel Ice 0.027 —
Steel Grey Iron 0.20 0.10
Steel Steel 0.15 0.10
Steel White Metal — —
Wood Ice — —
Wood Wood 0.65 0.16
Leather Grey Iron 0.55 0.22
Brake Lining Steel — —
Steel Nylon (polyamide) — —
Material Coefficient of Static Friction µ
0
Dry Lubricated
Bronze Bronze 0.2 0.06
Bronze Grey Iron 0.21 0.08
Grey Iron Grey Iron — 0.12
Steel Bronze 0.18 0.07
Steel Ice 0.014 —
Steel Grey Iron 0.16 0.05
Steel Steel 0.10 0.05
Steel White Metal 0.20 0.04
Wood Ice 0.035 —
Wood Wood 0.35 0.05
Leather Grey Iron 0.28 0.12
Brake Lining Steel 0.55 0.40
Steel Nylon (polyamide) 0.5 0.10
Example: A steel component with a weight of 500 kg is to be
pulled across bronze plate without lubrication. What will the
frictional force be when the component moves?
F
static
= F
n
x µ
0
F
kinetic
= F
n
x µ
F
static
= 500 x 9.81 x 0.27 = 1324 N
F
kinetic
= 500 x 9.81 x 0.18 = 883 N
The static frictional force should always be compared with the
force provided by the motor when it starts.
Kinetic Resistance
Kinetic resistance is a term expressing the total resistance,
consisting of rolling resistance and the frictional force in the
bearing.
Formula:
F
F
= µ
F
x F
n
F
F
= kinetic resistance in N
µ
F
= coefficient of kinetic resistance
F
n
= force from object in N
Coefficient of Kinetic Resistance:
Object Coefficient of Kinetic
Resistance
Railway vehicle on steel rails 0.0015 to 0.0030
Vehicle with rubber wheel on asphalt 0.015 to 0.03
Example:
A railway carriage with a weight of 2 tons is to move over flat
rails. What will the kinetic resistance be?
F
F
= µ
F
x Fn
F
F
= 0.0030 x 2 x 1000 x 9.81
F
F
= 4.86 N
F
n
F
F
Fstatic
F
kinetic
Fn
Ffriction
Catalog 0900P-E
Technical Data