# Collision

We also want the gem to go back to the top if it touches the spaceship. If you had done Scratch before, you might remember the `if touching sprite` command. In Pygame Zero, we'll use `if gem.colliderect(ship):` or `if ship.colliderect(gem):` (...both works the same).

``````if gem.colliderect(ship):
gem.y = 0
``````

...or...

``````if ship.colliderect(gem):
gem.y = 0
``````

Try it out!

# Random

It's not vey interesting to have the gem fall from the same spot everytime. In Introduction to Python, you learned to use the `random` module. We'll use it here to randomize the x position of the gem.

Before we can use the `random` module, we'll need to import it.

``````import random
``````

To assign a random x position, we use...

``````gem.x = random.randint(20, 780)
``````

The `random.randint(20, 780)` function will provide a random number between 20 to 780. This should be added whenever we return the gem to the top of the screen.

Your program should look like this now.

``````import pgzrun
import random

WIDTH = 800
HEIGHT = 600

ship = Actor('playership1_blue')
ship.x = 370
ship.y = 550

gem = Actor('gemgreen')
gem.x = random.randint(20, 780)
gem.y = 0

def update():
if keyboard.left:
ship.x = ship.x - 5
if keyboard.right:
ship.x = ship.x + 5

gem.y = gem.y + 4
if gem.y > 600:
gem.x = random.randint(20, 780)
gem.y = 0
if gem.colliderect(ship):
gem.x = random.randint(20, 780)
gem.y = 0

def draw():
screen.fill((80,0,70))
gem.draw()
ship.draw()

pgzrun.go() # Must be last line
``````