diff --git a/2020/sketch_2020_07_31a/particles.py b/2020/sketch_2020_07_31a/particles.py
new file mode 100644
index 00000000..037c79c4
--- /dev/null
+++ b/2020/sketch_2020_07_31a/particles.py
@@ -0,0 +1,103 @@
+
+
+class Particle:
+    
+    F = 10
+
+    def __init__(self, position, PS):
+        self.acceleration = PVector(0, 0)
+        self.velocity = PVector(random(-1, 1) / 5, random(-1, 1) / 5)
+        self.position = position.copy()
+        self.timeToLive = 255.0
+        self.mass = random(5, 50)
+        self.PS = PS
+
+    def run(self):
+        self.update()
+        self.display()
+
+    def applyForce(self, force):
+        # print self.acceleration
+        self.acceleration += force / self.mass
+
+    def update(self):
+        for p in self.PS.particles:
+            if p is self:
+                break
+            else:
+                dir = self.position - p.position
+                # Distance between objects
+                d = dir.mag()
+                # Normalize direction vector
+                dir.normalize()
+                # Keep distance within a reasonable range
+                d = constrain(d, 1, 100)
+                # Repelling force is inversely proportional to distance
+                force = 1 * self.F / (d * d)
+                # print force
+                force = constrain(force, 0, 50)
+                if force > 10:
+                    print force
+                # Get force vector -= 1: magnitude * direction
+                dir *= -force
+    
+                self.applyForce(dir)    
+                p.applyForce(dir * -1)
+    
+        
+        self.velocity += self.acceleration
+        self.position += self.velocity
+        self.acceleration.setMag(0)
+        # # self.timeToLive -= 1
+        self.velocity *= .95
+         
+        if self.position.x > width + 50: self.position.x = -50
+        if self.position.x < -50: self.position.x = width + 50
+        if self.position.y > height + 50: self.position.y = -50
+        if self.position.y < -50: self.position.y = height + 50
+
+    def display(self):
+        # stroke(0, 0, 0, self.timeToLive)
+        # strokeWeight(2)
+        noStroke()
+        fill(self.mass * 5, 200, 200, 255)#self.timeToLive)
+        ellipse(self.position.x, self.position.y, self.mass, self.mass)
+
+    def isDead(self):
+        if self.timeToLive < 0.0:
+            return True
+        else:
+            return False
+
+class ParticleSystem():
+
+    def __init__(self, position):
+        self.origin = position
+        self.particles = []
+
+    def addParticle(self, pos=None):
+        pos = pos or self.origin
+        self.particles.append(Particle(pos, self))
+
+    def applyForce(self, force):
+        for p in self.particles:
+            p.applyForce(force)
+
+    def applyGravity(self):
+        for p in self.particles:
+            p.applyForce(gravity * p.mass)
+
+    def applyRepeller(self, r):
+        for p in self.particles:
+            force = r.calculateRepelForce(p)
+            p.applyForce(force)
+
+    def run(self, force=None):
+        for p in reversed(self.particles):
+            p.run()
+            
+            if force is not None:
+                self.applyForce(force)
+            
+            if p.isDead():
+                self.particles.remove(p)
diff --git a/2020/sketch_2020_07_31a/sketch_2020_07_31a.gif b/2020/sketch_2020_07_31a/sketch_2020_07_31a.gif
new file mode 100644
index 00000000..342cd681
Binary files /dev/null and b/2020/sketch_2020_07_31a/sketch_2020_07_31a.gif differ
diff --git a/2020/sketch_2020_07_31a/sketch_2020_07_31a.pyde b/2020/sketch_2020_07_31a/sketch_2020_07_31a.pyde
new file mode 100644
index 00000000..387841d2
--- /dev/null
+++ b/2020/sketch_2020_07_31a/sketch_2020_07_31a.pyde
@@ -0,0 +1,38 @@
+add_library('video')    # import processing.video.*
+add_library('opencv_processing') # import gab.opencv.*
+
+
+from particles import ParticleSystem
+
+def setup():
+    global video, opencv, particles
+    size(400, 400)
+    video = Capture(this, 640/2, 480/2)
+    opencv = OpenCV(this, 640/2, 480/2)
+    video.start()
+
+    particles = ParticleSystem(PVector(width / 2, 50))
+    # repeller = Repeller(width / 2, 280, power=20000)
+    colorMode(HSB)
+    for _ in range(20):
+        particles.addParticle(PVector(random(width), random(height)))
+
+
+
+def draw():
+    background(0)
+    opencv.loadImage(video)
+    opencv.calculateOpticalFlow()
+    ave_flow = PVector().set(opencv.getAverageFlow())
+    print ave_flow
+    if not ave_flow.x != ave_flow.x:
+        particles.run(ave_flow)
+
+    stroke(255)
+    scale(1.5, 2)
+    opencv.drawOpticalFlow()
+
+
+        
+def captureEvent(c):
+    c.read()
diff --git a/README.md b/README.md
index 5dbdeb78..6f9698b0 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,12 @@
 
 ---
 
+![sketch_2020_07_31a](2020/sketch_2020_07_31a/sketch_2020_07_31a.gif)
+
+[sketch_2020_07_31a](https://github.com/villares/sketch-a-day/tree/master/2020/sketch_2020_07_31a) [[Py.Processing](https://villares.github.io/como-instalar-o-processing-modo-python/index-EN)]
+
+---
+
 ![sketch_2020_07_30d](2020/sketch_2020_07_30d/sketch_2020_07_30d.gif)
 
 [sketch_2020_07_30d](https://github.com/villares/sketch-a-day/tree/master/2020/sketch_2020_07_30d) [[Py.Processing](https://villares.github.io/como-instalar-o-processing-modo-python/index-EN)]