# Strange Kinetic frictional force values

**URL:** <https://forums.unrealengine.com/t/strange-kinetic-frictional-force-values/490821>\
**Category:** World Creation\
**Tags:** friction, unreal-engine, Physics, question\
**Created:** [November 19, 2021, 7:01am UTC](https://forums.unrealengine.com/t/strange-kinetic-frictional-force-values/490821 "2021-11-19T07:01:12Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Shadowfax2021](https://d1ap1mz92jnks1.cloudfront.net/user_avatar/forums.unrealengine.com/shadowfax2021/32/88717_2.png) [@Shadowfax2021](https://forums.unrealengine.com/u/Shadowfax2021)\
**Post date:** [November 19, 2021, 7:01am UTC](https://forums.unrealengine.com/t/strange-kinetic-frictional-force-values/490821/1 "2021-11-19T07:01:12Z")

</div>

As being new to UE4, I’m testing simple scenarios and at this time I tried to learn how friction factor influence the object’s movement.

**First experiment - zero friction**

I set a physical material with zero friction for both, a floor and a cube, then add one shot of force of 1N to the cube within axis x:

- FPS = fix 40fps (so tick time step = 0.025s)
- Gravity = -2000cm/s^2 (just in order to have nice numbers)
- Cube mass = 1kg
- Physical Material Friction = 0.0
- addForce = 1N

The change of velocity should be:

- TickStepTime = 1/fps = 0.025s
- addForce = 1N
- velocity change after one shot of force = 1N\*0.025s/1kg = 0.025m/s = 2.5cm/s

And this is exactly what I get

![351952-test8noriction.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/f/f/2/ff2372d10ac8f8ec73acaceebfbd2317e3342cf8.png)

**Second experiment - friction value = 0.025**

At this time, the expected kinetic frictional force should be:

- weight of cube = 2000cm/s^2 \* 1kg = 20N
- the kinetic frictional force should be then = 0.025 \* 20N = 0.5N

The change of velocity after the force shot should be:

- TickStepTime = 1/fps = 0.025s
- addForce = 1N
- kinetic frictional force = 0.5N
- velocity change after one shot of force = (1N-0.5N)\*0.025s/1kg = 0.0125m/s = 1.25cm/s

But the results are strange - velocity is not only at x axis, and there even ticks where the x velocity is negative as shown in the snapshot.  
Even the first velocity value is 0.396 cm/s and is absolutely far from the expected value 1.25cm/s

![351953-test8friction.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/f/8/2f8025791fd826755f94b76b2ca2e8e3e2dc029a.png)

I will be glad for a help for understanding how to fit the UE4 physics behavior to the expected values.

Thanks.

========================================================================

Settings and cube blp snapshots attached here

========================================================================

 ![351954-test8settings.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/5/a/8/5a8cdce4ed267e5da04f44355d0974331459749e.png)

 ![351955-test8cube-blp.png](https://d3kjluh73b9h9o.cloudfront.net/original/4X/e/6/c/e6c558d6fa27c1b312cb551e30e1f8013e48c66b.png)