Dan Ebberts provides example expressions and tutorials for learning how to work with expressions on his MotionScript website. For example, Dan provides an excellent page about collision detection.

Trish and Chris Meyer provide a series of articles about expressions on the ProVideo Coalition website. These articles contain many useful examples.

Colin Braley provides a tutorial and example project on his website that show how to use expressions to make one layer repel others in a natural-seeming manner.

The AE Enhancers forum provides many examples and much useful information about expressions, as well as scripts and animation presets. In this post on the AE Enhancers forum, Paul Tuersley provides a tutorial and example project that show how to use expressions to animate several layers in a swarm.

Rick Gerard provides an example on his website that demonstrates rolling a square object along a floor so that the sides stay in contact with the floor plane.

Carl Larsen provides a video tutorial on the Creative COW website that demonstrates how to use expressions and parenting to relate the rotation of a set of wheels to the horizontal movement of a vehicle.

Marcus Geduld provides some examples from his book, After Effects Expressions, on the Focal Press website. In the "String Manipulation" section, Marcus shows how to use basic JavaScript to manipulate the text in the Source Text property of a layer. He even shows how to use an array of strings so that a layer's Source Text property can be set to a specific word from a list. In the "Physical Simulations" section, Marcus shows how to use expressions for orbits, bounces, jiggles, and collision detection.

Chris Zwar provides an example project on his website for automatically arranging still images or videos into a grid (like a video wall). You can easily adjust position and spacing with sliders that are connected to a system of expressions. There are three compositions in the project—one for stills, one for videos, and one to create an auto-storyboard in which a video is sampled at user-defined intervals and aligned into a grid.

JJ Gifford’s website provides several example projects that demonstrate how to use expressions.

Rhys Enniks provides a video tutorial on his website in which he uses expressions and multiple text animators and range selectors to animate text as if it is being typed onto a computer screen.

Maltaannon (Jerzy Drozda, Jr.) provides a video tutorial on his website that shows how to use expressions to create a volume meter using the results of the Convert Audio To Keyframes command.

Harry Frank provides a tutorial on his graymachine website that shows how to use expressions to read data from an external text file.

1. Select a layer, press P to reveal its Position property in the Timeline panel, and Alt-click (Windows) or Option-click (Mac OS) the stopwatch to the left of the property name.
2. Enter the following in the expression field:

     [(thisComp.width/2), (thisComp.height/2)] + [Math.sin(time)*50, -Math.cos(time)*50]

1. Import or create two long, narrow solid-color layers: an hour hand and a minute hand. (See Solid-color layers and solid-color footage items.)
2. Set the anchor points at the ends of the layers. (See Layer anchor points.)
3. Move the layers so that the anchor points are at the center of the composition. (See Move layers in space.)
4. Set Rotation keyframes for the hour hand. (See Set or add keyframes.)
5. Select the Rotation property for the minute hand and choose Animation > Add Expression.
6. Drag the pick whip to the Rotation property for the hour hand. The following expression appears:

     thisComp.layer("hour hand").rotation

7. To make the minute hand rotate 12 times as fast as the hour hand, add *12 at the end of the expression as follows:

     thisComp.layer("hour hand").rotation*12

1. Start with three layers. (See Creating layers.)
2. Animate the positions of the first two layers in the Timeline panel. (See Motion paths.)
3. Select the third layer, press P to reveal the Position property, and Alt-click (Windows) or Option-click (Mac OS) the stopwatch button to the left of the property name.
4. Enter the following in the expression field:

     (thisComp.layer(1).position + thisComp.layer(2).position)/2

1. Start with two solid-color layers that are scaled to approximately 30% of the composition size. (See Solid-color layers and solid-color footage items.)
2. Animate the position of the first layer. (See Motion paths.)
3. Select the second layer, press P to reveal the Position property, and Alt-click (Windows) or Option-click (Mac OS) the stopwatch button to the left of the property name.
4. Enter the following in the expression field:

     thisComp.layer(thisLayer, -1).position.valueAtTime(time - .5)

5. Duplicate the last layer five times by selecting it and pressing Ctrl+D (Windows) or Command+D (Mac OS) five times.

1. Start with two layers. Make one layer a magnifying glass or similar object with a hole in the middle and name it Magnifier. (See Creating layers.)
2. Animate the position of the magnifying glass layer. (See Motion paths.)
3. Apply the Bulge effect to the other layer. (See Apply an effect or animation preset.)
4. Select the Bulge Center property of the Bulge effect in the Timeline panel and choose Animation > Add Expression, or Alt-click (Windows) or Option-click (Mac OS) the stopwatch button for the property.
5. Select the default expression text and type the following:

     fromWorld(thisComp.layer("Magnifier").position)

• Apply the following expression to a property to wiggle it beginning at time 2 seconds:

    timeToStart = 2; 
    if (time > timeToStart){ 
        wiggle(3,25); 
    }else{ 
        value; 
    }

• Apply the following expression to a property to stop wiggling it at time 4 seconds:

    timeToStop = 4; 
    if (time > timeToStop){ 
        value; 
    }else{ 
        wiggle(3,25); 
    }

• Apply the following expression to a property to start wiggling it at time 2 seconds and stop wiggling it at time 4 seconds:

    timeToStart = 2; 
    timeToStop = 4; 
      
    if ((time > timeToStart) && (time < timeToStop)){ 
        wiggle(3,25); 
    }else{ 
        value; 
    }