How do I make a cannon fire a cannonball with momentum?

I am looking for a way for a click to cause a cannon to fire a cannonball that has momentum?

You'll have to be more specific with what you mean by momentum. If you use the bullet behavior on the cannonball it will move on it's own. You could use the physics behavior instead to make it be able to interact with other physics objects.

This may help..not sure though. I made a capx file but it won't let me post it because i have no reputation. Sorry!

When the mouse is clicked i want the cannon to fire a cannonball at a certain velocity and for it to have physics. How would I do this?

Well you add the physics behavior to the object that the cannon fires(lets call it cannonball) and then you have events:

Event : on cannon touched(or tapped, or clicked, etc.)

Actions: cannon spawn object cannonball on layer XX

cannonball apply physics force XX at angle cannon.angle + XX

And just replace the XX's with the values you want.

But the angle is where the cannon is facing because it follows my arrow so?

If you make the cannon ball a "bullet" using the bullet behaviour you can set the gravity.

https://www.scirra.com/manual/90/bullet

I guess that's what you mean?'

I got help with a similar problem in this thread before. Maybe this can help you out.

https://www.scirra.com/forum/viewtopic.php?f=147&t=148511

But the angle is where the cannon is facing because it follows my arrow so?

That is why I said replace the XX's with the values you want. In this case(if I understand you question correctly) the expression should be:

cannonball apply physics force XX at angle cannon.angle + 90

I've done it, thanks guys.