Realistic values for air resistance and friction

Hiya, say I have a ball that I throw in the air in an arc, I want to slow it down in the air by air resistance and on the ground by friction - oh and it needs to bounce. I'm assuming no wind.

I know the ball could have all sorts of different textures that may affect the air resistance and friction, so assume it's pretty smooth like plastic (not like a polished thing). Also assume the ground is very well maintained short grass without unusual bumps, not a mirror smooth surface.

Naturally I'll be applying gravity and making it bounce (I'll set the ball up with an appropriate Young's Modulus).

I'm wondering if it's worth applying air resistance at all or if it'll be such a low amount as to not be worth bothering.

Mainly the ball needs to slow down when rolling on the ground towards the end but should I retard the horizontal velocity as a result of it bouncing? (probably should do) Naturally I'll be changing the vertical velocity as a result of the bounce. Then they'll be a point when it ceases to bounce and just rolls and that's when my friction really kicks in, so I need a realistic value.

I know I could go more complex than this by introducing spin, but I want to keep it simple.

Assume ball is moving in metres per second so the friction values can be related to that.

Any suggestions appreciated, thanks!

Depends on the size of the cross-section of the ball.

OK well the ball is pretty small, maybe 5cm across.

If you don't apply air resistance what else is going to slow it down - aside from ground friction or impacts? You have to apply it in my book. Just set a value and tweak it - that's what I do until it moves 'realistically' within the game-play tolerances I want.

Does it need to be super-realistic/accurate. Can't you just tweak the variables until it looks right?

Hujiklo: Ground friction and impacts seem to work pretty well, but maybe I'll apply a bit of air friction too, I dunno.

big10p: Well yeah, but I wanted to start with some good values :-) Looks OK at the moment actually, but I think I need to let it roll further.

For sure it's worth applying air resistance if you want to design something realistic
The book "Physics for game developer" by David Bourg supplies coefficients and curves for air resistance and friction

Air Friction is exponential in nature. The faster the ball moves, the more air friction will resist that movement. The converse is also true. The slower the ball moves, the less affect air friction will have on the ball.

What this means is that if you fire the ball out of a cannon, it will slow down rapidly initially, but after that initial deceleration it will continue moving at a slower rate of speed for a very long time.

So if you were making a tennis game, you might want the ball to slow down a bit after it's hit due to air friction, but the real reason it comes to a stop eventually is due to losses when it hits the ground due to the inelastic component of the collision.

What I'm saying is that the effect you want, you probably won't get by applying air friction.

http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/josh_fritts/flight.html

Alberto: It doesn't need to be ultra realistic, just realistic enough, so I wondered if air resistance was worth bothering with, it may not be.

sswift: you mean "inverse" ;-) converse is a brand of shoes. Yep I see, so more initial slowdown based on speed. I'm also applying energy loss when it hits the ground, and this works fine. At a certain point I'm stopping it from bouncing and making it "roll" but this is causing me hassle at the moment, I'm sure I'll crack it.

Indiepath: Thanks. very appropriate.

If you're doing things right, rolling should occur naturally - when a bounce means not enough energy is left in the ball to counter gravity?

P.S. What's wrong with 'converse'? :)

oh OK then :-) I'll use it all the time now ;-)

Yeah got the rolling working. Part of the problem is the order you do things. Do you take off gravity first, or after you bounced etc? It has a subtle but important effect on stuff because in reality it all occurs at once, but in a program stuff happens in a linear fashion and is looped rapidly - this is not the same of course.

Grey:
If you expect me to converse with you, I expect you to know the meaning(s) of converse!

yeah sorry dude :-)

Don't let it happen again, or I shall have to reebok you once more!