Main Difference – Dynamic vs. Kinematic Viscosity

This update allows us to accurately model the physical characteristics of a robot to achieve more realistic kinematic simulations. When installed in the Unity Editor, this package allows the user to select a URDF file to import. It parses the XML file behind the scenes and stores the links and joints in the appropriate C# classes.

Viscosity is very important to any process that depends on a flow of fluid. Usually, two types of viscosity are quoted: dynamic and kinematic viscosity. The main difference between dynamic and kinematic viscosity is that dynamic viscosity is a measurement of how difficult it is for a fluid to flow whereas kinematic viscosity is the dynamic viscosity of a fluid divided by its density.

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• I'm using Unity 2019.4.2f1 personal. I'm getting exception: Non-convex MeshCollider with non-kinematic Rigidbody is no longer supported since Unity 5. If you want to use a non-convex mesh either make the Rigidbody kinematic or remove the Rigidbody component. Scene hierarchy path. I have a parent GameObject with some components including a.
• Then there's Unity's kinematic motion. In that model, a rigid body like a door is not affected by gravity and cannot be pushed out of the way by a user or dynamic object striking it. It moves, yet it itself is immovable.

What is Dynamic Viscosity

Whenever a fluid flows against a surface, the different layers of fluid exert frictional forces between each other, causing them to flow at different speeds. A force needs to be applied to a layer of fluid in order to make it flow at a constant speed relative to any other layer. The force required to move a layer of fluid in this way is related to the velocity at which the fluid layer will move by the equation:

where is the area of the layer and is the distance between the layers. is a constant of proportionality, and it is known as the dynamic viscosity of the fluid. In this sense viscosity is a measurement of how difficult it is to make a fluid flow. Note that the above equation is only valid for so-called Newtonian fluids. Non-Newtonian fluids cannot be described with one value for viscosity.

Honey is more viscous than water, and so it is more difficult to get it flowing.

The forces between different layers exert a type of shear stress since the forces act parallelly to the layers. For this reason, dynamic viscosity is also called shear viscosity. Dynamic viscosity is also referred to as absolute viscosity at other times. The SI unit of measuring dynamic viscosity is pascal seconds (Pa s). However, the most commonly-used unit for measuring viscosity is the centipose (cP). 1000 cP = 1 Pa s.

What is Kinematic Viscosity

Kinematic viscosity () of a fluid is the ratio of the fluid’s dynamic viscosity to its density :

The SI unit of kinematic viscosity is m² s^-1. However, the more commonly-used unit for measuring kinematic viscosity is the centistoke (cSt). 10⁶ cSt = 1 m² s^-1. Note that since viscosity depends on temperature (the viscosity decreases as temperature increases in liquids, while the viscosity decreases when the temperature of a gas increases). When the viscosity of a substance is quoted, the temperature should be specified.

Difference Between Dynamic and Kinematic Viscosity

Involvement of Density

Both dynamic and kinematic viscosities measure how difficult it is for a fluid to flow. Kinematic viscosity measures this in terms of density, whereas dynamic viscosity does not.

Units of Measurement

Unity Kinematic Rigidbody Velocity

Dynamic viscosity has SI units of Pa s. It is more commonly measured in centipose (cP).

Kinematic viscosity has SI units of m² s^-1. It is more commonly measured in centistokes (cSt).

Image Courtesy

“Viscosity Manifest” by Beny Shlevich (Own work) [CC BY 2.0], via flickr

Unity Is Kinematic

For this short Unity Lesson, I teach you what the is Kinematic option does on the Rigidbody component in Unity. The is kinematic setting makes it so that the rigidbody object will not move because of Physics.

Unity3d Iskinematic

Now you might be wondering, why would you want to attach a rigidbody component to an object only to disable to physics of the object? The answer is that sometimes you want an object to be stationary until a certain point and only after something happens do you want the object to interact with physics. At that point, all you have to do is disable the is kinematic option.

Unity Kinematic Vs Dynamic

For example in my Zig Zag tutorial series I want the platforms to eventually fall but not until that ball touches the platform and then leaves the platform. This will then make it look like all the platforms are falling just behind the ball.