Friction: "the force that resists relative motion between two bodies in contact"

Merriam Webster
Friction force is tangential to the contacting surfaces of the two bodies.
Contact force act perpendicular or "normal" to the surfaces of the contacting bodies.

see Figure 1

Figure 1: The friction force between two objects is realted to the force of contact. The coefficient of friction is computed as the simple ratio of friction force to contact force. The tanget can be computed on a calculator or using the graphic in (b).

Published hand friction Data

Material
(n=42)		 Dry Moist
(n=42)		 Combined
(n=84)
Sand Paper (#320) -- -- 0.61±0.10
Smooth Vinyl -- -- 0.53±0.18
Textured Vinyl -- -- 0.50 + 0.11
Adhesive Tape 0.41±0.10 0.66±0.14 --
Suede 0.39±0.06 0.66±0.11 --
Aluminum -- -- 0.38±0.13
Paper 0.27±0.0 0.42±0.07 --

Buchholz B, Frederick L Armstrong T. An investigation of human palmar skin friction and the effects of materials, pinch force and moisture. Ergonomics 31(3):317-325, 1988.

Bobjer O, Johansson SE, Piguet S. Friction between hand and handle. Effects of oil and lard on textured and non-textured surfaces; perception of discomfort. Applied Ergonomics. 1993 Jun 1;24(3):190-202.

A simple method for measuring static coefficient of friction, CoF

The static CoF can be estimated by placing an object on a flat hand and calculating the tagent of the tilt angle at which the object begins to slide (see Figure 2). The CoF will be affected by many factors such as the moistness of the skin and the weight of the object.

       
Figure 2: The object shown in (a) will begin to slide when the gravity force exceeds friction force between the hand and the object. The static coeficient of friction, CoF, can be computed as the tangent of the angle, θ, at which the object begins to slide (a). The tanget can be computed on a calculator or using the graphic in (b).

Seo N, Armstrong T, Drinkaus P. A Comparison of Two Methods of Measuring Static Coefficient of Friction at Low Normal Forces: A Pilot Study. Ergonomics 52(1):121-135, 2009.