Time for action – starting physics for the paddle and ball

Right now, our display objects are rather stagnant. In order for the game play to initiate, we have to activate physics for collision detection to occur between the paddle and ball. Perform the following steps:

Above the gameLevel1() function, create a new function called startGame():
```
function startGame()
```

Add in the following lines to instantiate the physics for the paddle and ball:

  physics.addBody(paddle, "static", {density = 1, friction = 0, bounce = 0})
  physics.addBody(ball, "dynamic", {density = 1, friction = 0, bounce = 0})

Create an event listener that
uses the background display object to remove the "tap" event for startGame(). Close the function with end:
```
  background:removeEventListener("tap", startGame)
end
```
In the addGameScreen() function that we created in the previous chapter, we have to add the following line after the call to the gameLevel1() function. This starts the actual game when the background is touched:
```
  background:addEventListener("tap", startGame)
```

What just happened?

The paddle object has a "static" body type, so it is not affected by any collision that occurs against it.

The ball object has a "dynamic" body type because we want it to be affected by the collisions on the screen due to directional changes caused by the wall borders, bricks, and paddle.

The event listener on the background is removed from the startGame() function; this way, it doesn't affect any of the other touch events that are applied in the game.