What the fric.....tion?

[Urb4n0ninj4]

Are there plans to add friction in the game? Any would be nice... Watching Rovers and Kerbals alike slide across the rocky Mun surface (or any surface, really) like it's made of ice has spelled frustration and doom for many a mission.

Anyone know of decent mods that might add something to the game to satiate my need for a more realistic planet surface in the meantime?

My slippery Kerbals thank you all in advance.

[EdFred]

Well, keep in mind that mu is reduced quite a bit when gravity is also reduced. However it would be cooler if they bounced rather than slid.

[hellion13]

Ground friction really only works if there is enough gravity. The Mün doesn't really have enough.

Also, check your speed the next time you go skittering across the ground.

[Urb4n0ninj4]

Oh, I agree that the low gravity affects the movement of kerbals and vehicles alike. But get your kerbal going 5m/s horizontally and let him hit the surface, and he will slide like the surface is smooth as silk. I would just like to see it act like the surface is made of the dust, dirt, and particulate it is visually represented as. It would make things a little more predictable. Though I'll admit the slippery surface is humorous...but keep it to Minmus' frozen lakes.

[CalculusWarrior]

A source of friction I'd like to see added would be between the kerbals and spaceships. Right now if you have a kerbal standing on a rover, they will slip off as soon as you start driving. It's a small feature, I know, but it would be pretty cool to see.

[Urb4n0ninj4]

A source of friction I'd like to see added would be between the kerbals and spaceships. Right now if you have a kerbal standing on a rover, they will slip off as soon as you start driving. It's a small feature, I know, but it would be pretty cool to see.

Totally agree. I hate how helpless they are

I see it on ladders mostly though, when you get out of a vehicle they just slide up or down until they reach the end, and off into space.

[paul23]

Well, keep in mind that mu is reduced quite a bit when gravity is also reduced. However it would be cooler if they bounced rather than slid.

Sliding is caused by gravity - and is reduced by the same factor.. So lower gravity (for same mass) shouldn't slide at less steep slopes. (BTW: mu is a material constant, however the maximum force before sliding is mu * normal force, where the normal force is of course gravity * cos(theta))

[comham]

There is something deeply wrong with surface friction in KSP, I imagine it's something that was set at a placeholder value 2 years ago and never changed, even after the addition of wheels.

[Urb4n0ninj4]

Sliding is caused by gravity - and is reduced by the same factor.. So lower gravity (for same mass) shouldn't slide at less steep slopes.

I dunno man, I am getting a lot of slipperiness on near-flat parts of the Mun, at as low as 5m/s. I'll have to get a video of it I s'pose. Not now, obviously...I'm at work (shh!)

[Depth]

Oh, I agree that the low gravity affects the movement of kerbals and vehicles alike. But get your kerbal going 5m/s horizontally and let him hit the surface, and he will slide like the surface is smooth as silk. I would just like to see it act like the surface is made of the dust, dirt, and particulate it is visually represented as. It would make things a little more predictable. Though I'll admit the slippery surface is humorous...but keep it to Minmus' frozen lakes.

5 meters per second = 18 KPH. Should quickly stop (or likely fall over) on Kerbin but in a low gravity environment there's not really anything there to stop you.

[zarakon]

When sliding across a flat surface, the deceleration will be equivalent to the acceleration due to gravity divided by the coefficient of kinetic friction.

The coefficient of friction depends entirely on the materials involved, but suppose it's 0.25 for a Kerbal sliding on the Mun. Since the Mun's gravity is 1.63 m/s^2, that means the Kerbal will decelerate at about 0.41 m/s^s. If you started sliding at just 5 m/s, it would take more than 12 seconds to slow down to a stop.

That 0.25 guess for the coefficient of friction might actually be pretty high, especially considering that the surface is likely covered in fine powder

[Urb4n0ninj4]

5 meters per second = 18 KPH. Should quickly stop (or likely fall over) on Kerbin but in a low gravity environment there's not really anything there to stop you.

Rocky loose ground? I mean if you infer from the splash page for the game, the rocket is dug into the ground, pretty well too...what's the impact tolerance of that command pod, like 17m/s? If it hit the Mun that soft and moved that much ground, I would think that a kerbal hitting the surface at 5m/s would still build up matter in front of him to slow him down.

I mean, I know that is just a fun little thing shown on the front of the game, but how else does one infer how loose the Mun surface is?

My ultimate point here is it seems friction across ALL bodies in the game is lacking, not just the Mun, Kerbin too.

[EdFred]

Sliding is caused by gravity - and is reduced by the same factor.. So lower gravity (for same mass) shouldn't slide at less steep slopes. (BTW: mu is a material constant, however the maximum force before sliding is mu * normal force, where the normal force is of course gravity * cos(theta))

Odd, I slid my hot tub up an inclined plane last week and onto my new deck. Must have been a gravitational flip that allowed me to do that.

[Urb4n0ninj4]

When sliding across a flat surface, the deceleration will be equivalent to the acceleration due to gravity divided by the coefficient of kinetic friction.

The coefficient of friction depends entirely on the materials involved, but suppose it's 0.25 for a Kerbal sliding on the Mun. Since the Mun's gravity is 1.63 m/s^2, that means the Kerbal will decelerate at about 0.41 m/s^s. If you started sliding at just 5 m/s, it would take more than 12 seconds to slow down to a stop.

That 0.25 guess for the coefficient of friction might actually be pretty high, especially considering that the surface is likely covered in fine powder

It's times like this I wish I took some physics classes...

[worir4]

Odd, I slid my hot tub up an inclined plane last week and onto my new deck. Must have been a gravitational flip that allowed me to do that.

Lol what?

Inclined bath tub, that can't end well...

Edited October 24, 2014 by worir4

[cantab]

Most spacecraft parts grip OK. It's the kerbals that really like to slide around, presumably the game represents them somewhat differently. And the wheels are iffy, IIRC it's what Unity provides in stock.

[EdFred]

Lol what?

Inclined bath tub, that can't end well...

Heh. Hot tub/jacuzzi. Not a bath tub. LOL

[LethalDose]

The statements above are correct: mu wouldn't be affected by gravity, but the normal force would be.

Sliding is caused by gravity - and is reduced by the same factor.. So lower gravity (for same mass) shouldn't slide at less steep slopes. (BTW: mu is a material constant, however the maximum force before sliding is mu * normal force, where the normal force is of course gravity * cos(theta))

force of gravity is g*cos(theta)*mass.

Odd, I slid my hot tub up an inclined plane last week and onto my new deck. Must have been a gravitational flip that allowed me to do that.

That's how an inclined plane works... it has nothing to do with friction.

[EdFred]

The statements above are correct: mu wouldn't be affected by gravity, but the normal force would be.

force of gravity is g*cos(theta)*mass.

That's how an inclined plane works... it has nothing to do with friction.

I thought I laid on the sarcasm thick enough for it to be picked up. My point was it slid uphill. Gravity wasn't causing the sliding.

[paul23]

Odd, I slid my hot tub up an inclined plane last week and onto my new deck. Must have been a gravitational flip that allowed me to do that.

In your bath tub you don't slide over the material (metal, and skin mu), instead you slide because of aqua planing, a small film of water is between you and the metal. @ above: Well then either KSP physics has a bug, or you didn't start from equillibrium. I think the latter, at which point the equation is increased with the object's momentum, adding an extra variable to the equation (speed). At this point to "keep sliding" you have to find the speed for which this equation holds true (considering a flat surface now to show how the mass falls into the equation):

F||move = d(mv)/dt = mu_dynamic * n

Considering for our car mass is constant with time (no rockets used for breaking, just sliding along ground), n is the normal force (= m * g for horizontal, or m * g * cos(theta) )

m * a = mu_dynamic * m * g => a = mu_dynamic * g.

So as you can see for the whole equation the breaking acceleration (for sliding) is only dependent on the mu_dynamic - this is a break which would normally be called "locked breaks, abs malfunctioning". To calculate the maximum breaking (AND acceleration!!!) force before you start sliding (note that mu_dynamic is always a lot higher than mu_static so you really dont' wish to go over that):

F <= mu_static * n

m * a <= mu_static * m * g

a <= mu_static * g

In other words the mass will once again divide out, and increasing the mass has no effect on how fast something will slide. The influence is the acceleration (so don't try to speed up too fast/break too fast) and most importantly the mu of the moon. Now I think there's a mistake in this mu_static as it seems on the moon you immediatelly start sliding, so this would mean that mu_static is 0?

Edited October 25, 2014 by paul23

[arkie87]

why not make mu (dimensionless coefficient of friction) upgradable as you unlock new parts/rover-wheels?

Default should be about 1. Perhaps advanced wheels can be 2? Or in Kerbol, maybe they figured out how to make mu = 10?