Scratch

This belongs in Help with Scripts. I will ask a Scratch Team member to move.

Hardmath123 wrote:

@your post: Yes, it is to a low level; but a more technically accurate way is:

forever
if <touching [ground v]?>
set [yvel v] to (1)
else
change [yvel v] by (-1)
end
change y by (yvel)

Foar acceleration due to gravity. 

EDIT: Don't forget to put it in a forever block. That's important. 

I made it scratchblocks. For better clarity.
To make it more realistic; (I came up with this myself - I'd appreciate some credit  )

change [yvel v] by (([0] - ((Gravity) / [20])) * (Weight)) //Gravity being the 
//strength for the gravity. 10 is Earth-like

Last edited by Splodgey (2012-03-14 11:55:47)

MoreGamesNow wrote:

Splodgey wrote:

I made it scratchblocks. For better clarity.
To make it more realistic; (I came up with this myself - I'd appreciate some credit  )

change [yvel v] by (([0] - ((Gravity) / [20])) * (Weight)) //Gravity being the 
//strength for the gravity. 10 is Earth-like

Weight doesn't effect gravitational acceleration.   

change [y-vel v] by ((-1) * (gravitational constant))

Unless you're talking about something as big as the moon, but if your project had the moon falling, you already have other physics problem (orbit? collisions? elasticity?).

well to make realistic gravity you can use the variables option. Just say
IF GREEN FLAG CLICKED
FOREVER
CHANGE Y BY YVEL.(just make a variable labeled xvel and yvel.)

IF GREEN FLAG CLICKED
FOREVER
SET YVEL. TO YVEL. MULTIPLIED BY .91

IF GREEN FLAG CLICKED
FOREVER
IF TOUCHING THIS
SET YVEL. TO 0
IF UP ARROW KEY PRESSED
CHANGE YVEL. BY 5
ELSE
SET YVEL. TO -0.5

you can use this.
The one's on the top will make you character change y position
the bottom one will make sure it doesn't go through the ground.

AgentRoop wrote:

this is what i always do for gravity:

when gf clicked
forever
  if <touching [ground]?>
    set [y velocity v] to (0)
  else
    change [y velocity v] by (-1)
  end
end

this will apply gravity, then, of course, do this:

when gf clicked
change y by (y velocity)

then, if you want to jump or something, make sure you set y velocity to a certain number (and make sure that it's positive) 

I hope this helps and I always use it because it's nice and simple. 

Fixed it a bit 

JDProducers wrote:

well to make realistic gravity you can use the variables option. Just say

when gf clicked
forever
change y by <yvel>

when gf clicked
forever 
set [yvel v] to <<yvel>*[0.91]>

when gf clicked
forever
if <touching [ground v]?>
set [yvel v] to [0] 
end
if <key [up arrow v] pressed?>
change [yvel v] by [5]
else
set [yvel v] to [-0.5]
end

you can use this.
The one's on the top will make you character change y position
the bottom one will make sure it doesn't go through the ground.

Fixed this one too! 

@Splodgey

The equation for the force of gravity is this:

F = G (mass_1 * mass_2) / (distance^2)

and

F = mass * acceleration

two of the masses cancel, resulting in:

acceleration = G * mass_1 / (distance^2)

So the acceleration of something falling towards earth is "G*(mass of earth)/( (distance from earth)^2).  "G" is just a constant, so acceleration is only based on the mass of the earth and the distance (basically "mass/(distance*distance)").  Admittedly, the Earth does accelerate towards you (at an acceleration based on your mass), but this is, in my opinion, negligible.  If you want to include the acceleration of the "world" towards you, and calculate an overall velocity, use this:

(G/(distance^2))((mass of earth)+(mass of you))

That should be it anyway 

Edit: the acceleration caused by you on the earth may not be enough to counter act what little friction there is on earth.  But that's just speculation on my part.

Edit (again): I just realized how appropriate my current quote is to this topic 

Last edited by MoreGamesNow (2012-03-17 20:49:03)