We have the ability to jump, but it still feels a bit off. This is because we’re not taking this pesky thing called gravity into consideration. Let’s see if we can adjust that a bit.

when green flag clicked
forever
	if <key [space v] pressed> then
		set [velocity v] to [10]
		repeat [21]
			change y by (velocity)
			change (velocity) by [-1]
		end
	end
end

What’s happening here?

• We start by setting a local variable for how much the sprite should jump.
• We repeat this just enough to go all the way up and then all the way back down.
  • We change the y position of the sprite by the velocity.
  • We then slow it down a bit.
  • At some point, it will become negative and sprite will settle back to where it began.

The alternative approach is to try to sense whether or not you’re on the ground end the jumping motion.

Using Multiplication

We can also try to do this by using multiplication.

when green flag clicked
forever
	if <key [space v] pressed> then
		set [y speed v] to (10)
		repeat (((y speed) * [2]) + [1])
			change y by (y speed)
			change [y speed v] by [-1]
		end
	end
end

Preventing the Rocket Ship Effect

The problem with this logic is that our hero will fly off the screen. We check to see if Arnold is not jumping before we let him jump.

when green flag clicked
forever
	if <key [space v] pressed> then
		if <(y speed) < [0]> then
			set [y speed v] to (10)
		end
		repeat (((y speed) * [2]) + [1])
			change y by (y speed)
			change [y speed v] by [-1]
		end
	end
end

Next, let’s look at adding and removing obstacles in our game.