Gravity: The Freefall

A study in gravity is more than just dropping objects off the Tower of Pisa. In animation, it involves several other factors that include velocity and wind drag—but ultimately, all objects in the natural world will find their way down. Falling objects need smooth motion. Don't use a sharp turn unless there's a clear reason for it, such as an outside force that changes the object's direction. A smartly placed blur will help sell the motion.

The first project we'll create in our study of gravity starts with a single image on a Photoshop layer. The orange will appear as if it is rolling on a surface and then drops off suddenly. Because there is some momentum to the rolling orange, it will not drop straight down along the very edge of the surface but will roll forward off the corner and then down at an arc.

1. Import the sliced orange file, OrangeSlicedSmall.psd on the DVD, into a new After Effects project as a composition—which retains the transparency around the orange.

2. Open the composition into a Comp window, and change the composition settings to 640 x 480 NTSC.

Note: If you want to follow along with a completed After Effects project file,you'll find GravityFall.aep as well as the completed QuickTime movie on the DVD in the Chapter 4 folder. I've included finished QuickTime versions of all the projects of this chapter.

Click the orange and move it to the upper half of the window. Make the rulers visible (View > Show Rulers; F/Alt+R) and drag down a guideline to the bottom of the orange's surface. Drag out a guideline from the left side to just past the halfway point. These guides will act as our surface and the edge of the drop-off (Figure 4.1).

Click the orange layer in the Timeline window, and drag the Current Time Indicator to the 1-second mark. Move the orange in the Comp window to the center of the vertical guide and touch the bottom edge with the horizontal guide.

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Figure 4.1

The guidelines will help us correctly animate the orange rolling off an imaginary table surface.

Figure 4.1

The guidelines will help us correctly animate the orange rolling off an imaginary table surface.

Press the P key on the keyboard to show the Position settings. Click the Stopwatch, and return the Indicator back to zero (or home key). Drag the orange in the Comp window off the left side of the window, keeping it in line horizontally with the previous position by holding down the Shift key while dragging the layer.

Press the R key to select the Rotation settings, and click the Stopwatch to set the current degree of rotation. Move the Indicator to the 1-second mark, and set the rotation to +180°.

Select RAM Preview to note the path your orange is moving, and make sure it is rotating the right amount for the motion path it's traveling. If it looks as if it's spinning on the surface, then adjust the degree of rotation at the 1-second mark to a lesser rotation. If it appears to be dragging on the surface, then increase the degree of rotation (Figure 4.2).

Figure 4.2

Adjust the rotation of the orange along the horizontal guide so that the orange appears to be rolling on a flat surface.

Figure 4.2

Adjust the rotation of the orange along the horizontal guide so that the orange appears to be rolling on a flat surface.

8. Return to the Timeline window and move the Indicator to 01:03 (three frames past the 1-second mark). In the Comp window, drag the orange down to the right of the intersection of the guidelines; use that intersection as an imaginary corner to the table, and place the orange at a 45° angle right on the corner. Set the rotation to an additional 45°.

9. Because there is no more contact with the table surface, the orange will drop down in a freefall, and it will spin approximately another 45° in the duration. Move the Indicator on the Timeline window to 01:10; then continue to move the orange down to the right and off the bottom of the Comp window, creating a slight arc from its departure from the table surface. Add an additional 45° to the rotation at the bottom point (Figure 4.3). Run a RAM Preview to see the motion path the orange takes.

Figure 4.3

The orange continues a slight rotation and at a slight arc because of the momentum created from rolling before the freefall.

£ This animation is now functional, but it still lacks visual realism during the

^ freefall. To enhance this, we will add a motion blur (Directional Blur) to the orange layer.

10. Move the Indicator on the Timeline window to the 01:03 mark, where the starting point of the freefall will begin the motion blur. Select Effect > Blur & Sharpen > Directional Blur, click the Stopwatch for the Blur Length settings in the Timeline window, and leave the default setting of zero at this point.

11. Move the Indicator to the 01:05 mark, click the Direction Stopwatch, and set the Direction to -60° and the Blur Length to 24 pixels (Figure 4.4).

12. Because the orange is still spinning slightly during the freefall, it is important to adjust the blur direction to keep it in a vertical motion blur. Move to the 01:10 mark and increase the Direction and Blur Length. I've selected a Direction of -105°, but you can adjust yours to get the arc you want. In addition to the rotation, the freefall of the orange is at a maximum toward the bottom of the Comp window, so I increased the Blur Length to 50 pixels.

Run a RAM Preview, and take note of any discrepancies in the animation motion path, rotation, or motion blur. Make minor adjustments accordingly. If the overall timing is an issue, then open up all of the settings in the Timeline window and select/drag an entire column of markers to the right or left to make adjustments (Figure 4.5).

Figure 4.3

The orange continues a slight rotation and at a slight arc because of the momentum created from rolling before the freefall.

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Figure 4.4 Adding a Directional Blur to the freefall portion of the animation will provide smoothness and realism,similar to the natural motion blur in video or film footage.

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Figure 4.5 Make global adjustments to the timing of the animation with an entire column of Timeline markers.

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