Have you ever observed why water flows easily when compared to ghee, coconut oil, honey, etc.? This is because the relative force between different layers of water is less when compared to the relative force between different layers of ghee, coconut oil, honey, etc. This relative force is called viscous force.
Flow of honey
Flow of water
When liquid flows, there is a frictional force between different layers of the liquid. If this force acts in a reverse order to stop the relative motion between layers of the liquid, it is referred as viscous force. Such a property of a liquid is called viscosity.
Viscous force is measured by or in S.I. units.
Where \(N\) stands for \(newton\).
In CGS Unit, the viscous forces are measured as \(Poise\) (\(P\)) or \(Pouseuille\)(\(PI\)) named after famous mathematician Jean Poiseuille.
Friction is a type of contact force, i.e. if the friction between your hand and the glass is high, then you can hold the glass firmly (or) with more grip.
A person holds a glass
Have you ever got a scolding from your mother for dropping a glass of water? Since your hands were oily, or you ate oily food before, because of the friction between your hands and the glass reduced by the oil. As a result, you drop the glass from your grip.
Highly viscous liquids such as oil, ghee can reduce the friction between the objects easily. Friction is possible between two moving bodies or bodies that tend to move. Friction always acts in a direction opposite to the moving bodies.