# Tutorial:Physics

In this example we will create a red ball that rolls around on a green ground.

The finished example is at the end of this page. All of these functions may be placed in one file: main.lua

We'll start in the love.load() function.

First we need to set up a world for the physics bodies to exist in.

```function love.load()
love.physics.setMeter(64) --the height of a meter our worlds will be 64px
world = love.physics.newWorld(0, 9.81*64, true) --create a world for the bodies to exist in with horizontal gravity of 0 and vertical gravity of 9.81```

Now that a world has been created, we can add bodies, shapes, and fixture to it.

```   objects = {} -- table to hold all our physical objects

--let's create the ground
objects.ground = {}
objects.ground.body = love.physics.newBody(world, 650/2, 650-50/2) --remember, the shape (the rectangle we create next) anchors to the body from its center, so we have to move it to (650/2, 650-50/2)
objects.ground.shape = love.physics.newRectangleShape(650, 50) --make a rectangle with a width of 650 and a height of 50
objects.ground.fixture = love.physics.newFixture(objects.ground.body, objects.ground.shape) --attach shape to body

--let's create a ball
objects.ball = {}
objects.ball.body = love.physics.newBody(world, 650/2, 650/2, "dynamic") --place the body in the center of the world and make it dynamic, so it can move around
objects.ball.shape = love.physics.newCircleShape( 20) --the ball's shape has a radius of 20
objects.ball.fixture = love.physics.newFixture(objects.ball.body, objects.ball.shape, 1) -- Attach fixture to body and give it a density of 1.
objects.ball.fixture:setRestitution(0.9) --let the ball bounce

--let's create a couple blocks to play around with
objects.block1 = {}
objects.block1.body = love.physics.newBody(world, 200, 550, "dynamic")
objects.block1.shape = love.physics.newRectangleShape(0, 0, 50, 100)
objects.block1.fixture = love.physics.newFixture(objects.block1.body, objects.block1.shape, 5) -- A higher density gives it more mass.

objects.block2 = {}
objects.block2.body = love.physics.newBody(world, 200, 400, "dynamic")
objects.block2.shape = love.physics.newRectangleShape(0, 0, 100, 50)
objects.block2.fixture = love.physics.newFixture(objects.block2.body, objects.block2.shape, 2)```

Now to wrap up the love.load() function, let's set up the screen size and background color.

```  --initial graphics setup
love.graphics.setBackgroundColor(0.41, 0.53, 0.97) --set the background color to a nice blue
love.window.setMode(650, 650) --set the window dimensions to 650 by 650 with no fullscreen, vsync on, and no antialiasing
end```

Okay, that's enough for the initial set up of the physics engine. Now we need to edit the love.update() function.

### love.update()

```function love.update(dt)
world:update(dt) --this puts the world into motion

--here we are going to create some keyboard events
if love.keyboard.isDown("right") then --press the right arrow key to push the ball to the right
objects.ball.body:applyForce(400, 0)
elseif love.keyboard.isDown("left") then --press the left arrow key to push the ball to the left
objects.ball.body:applyForce(-400, 0)
elseif love.keyboard.isDown("up") then --press the up arrow key to set the ball in the air
objects.ball.body:setPosition(650/2, 650/2)
objects.ball.body:setLinearVelocity(0, 0) --we must set the velocity to zero to prevent a potentially large velocity generated by the change in position
end
end```

Now that the world is updating, we can draw the ground and ball.

### love.draw()

First, the ground.

```function love.draw()
love.graphics.setColor(0.28, 0.63, 0.05) -- set the drawing color to green for the ground
love.graphics.polygon("fill", objects.ground.body:getWorldPoints(objects.ground.shape:getPoints())) -- draw a "filled in" polygon using the ground's coordinates```

And finally, we can draw the circle that represents the ball and the blocks.

```  love.graphics.setColor(0.76, 0.18, 0.05) --set the drawing color to red for the ball

love.graphics.setColor(0.20, 0.20, 0.20) -- set the drawing color to grey for the blocks
love.graphics.polygon("fill", objects.block1.body:getWorldPoints(objects.block1.shape:getPoints()))
love.graphics.polygon("fill", objects.block2.body:getWorldPoints(objects.block2.shape:getPoints()))
end```

There you have it! Put this file in a zip file, rename it to physics.love (or whatever), run it. And you'll have a ball rolling around in a lush green environment like I promised.

Screenshot of the mostly finished product.

## The main.lua

```function love.load()
love.physics.setMeter(64) --the height of a meter our worlds will be 64px
world = love.physics.newWorld(0, 9.81*64, true) --create a world for the bodies to exist in with horizontal gravity of 0 and vertical gravity of 9.81

objects = {} -- table to hold all our physical objects

--let's create the ground
objects.ground = {}
objects.ground.body = love.physics.newBody(world, 650/2, 650-50/2) --remember, the shape (the rectangle we create next) anchors to the body from its center, so we have to move it to (650/2, 650-50/2)
objects.ground.shape = love.physics.newRectangleShape(650, 50) --make a rectangle with a width of 650 and a height of 50
objects.ground.fixture = love.physics.newFixture(objects.ground.body, objects.ground.shape); --attach shape to body

--let's create a ball
objects.ball = {}
objects.ball.body = love.physics.newBody(world, 650/2, 650/2, "dynamic") --place the body in the center of the world and make it dynamic, so it can move around
objects.ball.shape = love.physics.newCircleShape(20) --the ball's shape has a radius of 20
objects.ball.fixture = love.physics.newFixture(objects.ball.body, objects.ball.shape, 1) -- Attach fixture to body and give it a density of 1.
objects.ball.fixture:setRestitution(0.9) --let the ball bounce

--let's create a couple blocks to play around with
objects.block1 = {}
objects.block1.body = love.physics.newBody(world, 200, 550, "dynamic")
objects.block1.shape = love.physics.newRectangleShape(0, 0, 50, 100)
objects.block1.fixture = love.physics.newFixture(objects.block1.body, objects.block1.shape, 5) -- A higher density gives it more mass.

objects.block2 = {}
objects.block2.body = love.physics.newBody(world, 200, 400, "dynamic")
objects.block2.shape = love.physics.newRectangleShape(0, 0, 100, 50)
objects.block2.fixture = love.physics.newFixture(objects.block2.body, objects.block2.shape, 2)

--initial graphics setup
love.graphics.setBackgroundColor(0.41, 0.53, 0.97) --set the background color to a nice blue
love.window.setMode(650, 650) --set the window dimensions to 650 by 650
end

function love.update(dt)
world:update(dt) --this puts the world into motion

--here we are going to create some keyboard events
if love.keyboard.isDown("right") then --press the right arrow key to push the ball to the right
objects.ball.body:applyForce(400, 0)
elseif love.keyboard.isDown("left") then --press the left arrow key to push the ball to the left
objects.ball.body:applyForce(-400, 0)
elseif love.keyboard.isDown("up") then --press the up arrow key to set the ball in the air
objects.ball.body:setPosition(650/2, 650/2)
objects.ball.body:setLinearVelocity(0, 0) --we must set the velocity to zero to prevent a potentially large velocity generated by the change in position
end
end

function love.draw()
love.graphics.setColor(0.28, 0.63, 0.05) -- set the drawing color to green for the ground
love.graphics.polygon("fill", objects.ground.body:getWorldPoints(objects.ground.shape:getPoints())) -- draw a "filled in" polygon using the ground's coordinates

love.graphics.setColor(0.76, 0.18, 0.05) --set the drawing color to red for the ball