The Classic Sudden Stop

What's the visual difference between a normal stop and a classic stop of an object? In the natural world, something with mass that's moving rapidly either rolls to a stop or needs a great deal of friction to bring it to a complete stop. If it's a solid object, a car for instance, it will most likely roll or skid to a stop. The only effect that inertia will have on it will be transferred through the tires, wheels, and suspension and to the body, which may move up and forward slightly and then come to rest back in its normal position.

However, in the cartoon world, the car's tires will just stop suddenly and the whole vehicle will bend or lurch forward, as if it were made of Jell-O. Then it will spring back slightly beyond its normal position before resting. This effect isn't confined to just classic cartoons; you will notice it in TV commercials and movies.

Let's do a simple experiment with this effect, using an image of a motorcycle. Create a new project in After Effects and a new composition, 640 x 480 NTSC. Import the file HD_V-Rod.psd from the Chapter 5 folder on the DVD as footage, and drag the PSD file into the Comp window (Figure 5.1).

Figure 5.1 Place the single-layer image onto the Comp window in the lower third of the frame.

Note: As always,you can see the final effect we're after here by viewing the finished Inertia-Stop movie on the DVD.

1. We need to first move the motorcycle across the screen, setting the start and stop points on the Timeline. Move the Indicator on the Timeline down to the Frame 17 mark, press the P key, and click the Stopwatch to set the stop point key frame.

2. Move the Indicator back to the Frame 6 mark, and drag the motorcycle layer out of the frame off to the left so it's out of view (Figure 5.2).

3. Move the Indicator down to approximately a half second so the motorcycle is visible in the Comp window. Apply the Transform effect to the motorcycle layer (Effect > Distort > Transform) and set the Skew to 20 at a +90° angle. Move the Indicator to Frame 21 and click the Skew stopwatch to set the key frame with the current amount of skew. Move the Indicator back to Frame 14 and set the amount of skew to 0.0, so the motorcycle isn't leaning all the way into the frame.

Figure 5.2

Create the start and stop points for the motion path of the motorcycle layer.

Figure 5.2

Create the start and stop points for the motion path of the motorcycle layer.

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4. The entire motorcycle skews from the center of the image, so we need to reposition the Anchor Point to the base of the motorcycle to make it lean forward at the tires (the center of rotation is at the ground level). Click the Anchor Point crosshair button in the Effects palette, and set the position manually in the Comp window (Figure 5.3). Because the effect is applied to the layer, it will make the motorcycle jump up to the layer's Anchor Point to match.

To make the motorcycle appear to lean forward under the force of inertia, the timing of the skew placement is important. The longer it takes for the effect to move forward before the recoil, the more energy appears to be applied to the motorcycle. If it's a short "snap back," then either the vehicle wasn't traveling very fast or the mass of the object is not that great.

5. After the skew forward is applied, move the Indicator down a few frames and reverse the skew at a lesser degree, and then move back to the upright unskewed position at rest (Figure 5.4). Apply the settings for the position and the applied Skew effect from Table 5.1; then use RAM Preview to see the timing of the effect.

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Figure 5.3

Apply a Skew effect to the layer to make the motorcycle lean forward, and reposition the Anchor Point to raise the bike into the frame so that the skew rotation is anchored at the ground level.

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Figure 5.3

Apply a Skew effect to the layer to make the motorcycle lean forward, and reposition the Anchor Point to raise the bike into the frame so that the skew rotation is anchored at the ground level.

To enhance the effect of the motorcycle's speed, let's add some motion blur. Select Effect > Blur & Sharpen > Directional Blur. Set the Direction to +90.0° and the Blur Length to 20.

Move the Indicator to Frame 17 in the Timeline, and click the Blur Length Stopwatch to set the key frame (Figure 5.5). Move the Indicator to Frame 20, and set the Blur Length to 0.0.

Figure 5.4 A reverse skew of a smaller degree provides the "snap back"of the effect.
Table 5.1 Position and Skew Effect

Effects:Transform

00;00

00;14

00;17

00;20

00;24

00;28

01;02

Anchor Point

223,228.5

Skew

0.0

20.0

20.0

-5.0

0.0

Skew Axis

+90.0°

Transform

Position

-230,320

350,320

Figure 5.5

Adding motion blur to the motorcycle will enhance the illusion of speed.

Figure 5.5

Adding motion blur to the motorcycle will enhance the illusion of speed.

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