Adhesion	[Newtons; N] the attractive contact force acting perpendicular to the substrate.
Friction	[Newtons; N] the contact force resisting motion parallel to the substrate.
Static friction	[Newtons; N] the friction force acting on a stationary object.
Dynamic friction	[Newtons; N] the friction force acting on a sliding object.
Contact area	[square meters; m2] the area of an adhesive in direct contact with a substrate.
Adhesive stress (Tenacity)	[Newtons per square meter; N/m2] the adhesion force per unit contact area. It provides a scale-independent representation of adhesive capacity.
Shear stress	[Newtons per square meter; N/m2] the friction force per unit contact area.
Fluid viscosity	[Newton seconds per square meter; N-s/m2] the resistance of a fluid to shearing. For example, honey is 10,000 times more viscous than water.
Substrate roughness	[nanometer; nm] the average height of the bumps, features, and asperities on a substrate.
Substrate energy	[milli-Newton per meter; mN/m] the excess energy that a surface of a material has compared to its bulk. If a substrate has high energy, then, generally, liquids and solids interact strongly with it.
Surface tension	[milli-Newton per meter; mN/m] the force (per unit length) acting tangential to a liquid-air interface. It is what enables insects to stand on the water surface and drives water drops to become spherical.
Young’s modulus (Stiffness)	[Pascals; Pa] the physical property that represents how easily a material can stretch or deform.