---
title: "Motion specification in animation"
subject: "Computer Graphics"
chapter: 1
key: "semester_5/computer_graphics:motion-specification-animation"
source: https://www.bctengineer.com/q/semester_5/computer_graphics/motion-specification-animation
site: BCT Engineering
---

# Motion specification in animation

Computer Graphics · Chapter 1: Introduction and Application

- Asked in: 2081 Chaitra (new course), 5 marks
- Video: [Motion Specification : Direct, Goal Directed system, Kinematics and Dynamics | lecture 5](https://www.youtube.com/watch?v=KowOTxoc0i4) — PolyTechGuru
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/computer_graphics/motion-specification-animation
- Whole chapter: https://www.bctengineer.com/md/semester_5/computer_graphics/chapter-1

## Question

Explain about motion specification in computer animation.

## Short answer

Motion specification methods include direct manual input, goal-directed commands, kinematic (forward/inverse), dynamic (physics-based forces), keyframe interpolation, and procedural scripted approaches.

## Answer

**Motion specification** tells the animation system how objects move, i.e. their position, orientation and size over time. The main methods are:

#### 1. Direct motion specification
The animator gives the position, rotation angles and scale factors for each frame or key time directly (e.g. rotate 30° and translate 5 units per frame). Simple but needs full manual control.

#### 2. Goal-directed (high-level) specification
The animator states the goal in general terms ("walk to the door", "pick up the cup") and the system works out the detailed motion. Used in robotics and character animation.

#### 3. Kinematic specification
Motion is given using position, velocity and acceleration, without considering forces.
- *Forward kinematics:* joint angles are given, end position is calculated.
- *Inverse kinematics:* the end position (e.g. hand) is given and the joint angles are calculated.

#### 4. Dynamic specification
Motion is calculated from physical forces and torques acting on objects, using Newton's laws (F = ma). Gives realistic motion such as falling, collision and cloth.

#### 5. Keyframe specification
The animator defines key frames (important positions), and the computer produces the **in-between frames** by interpolation (linear or spline).

```text
Key frame 1       in-betweens        Key frame 2
   O      ->     o    o    o    ->      O
```

#### 6. Procedural / scripted specification
Motion is controlled by an algorithm or script (e.g. particle systems, flocking, rotating fan).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. In direct specification the animator
   A. gives position, rotation and scale per frame or key time
   B. states a goal
   C. uses forces
   D. uses scripts
   Answer: A. Simple but manual. (Key point: Direct)

2. Inverse kinematics
   A. gives joint angles to compute end position
   B. gives end position and computes joint angles
   C. uses forces
   D. interpolates frames
   Answer: B. Forward is the reverse. (Key point: Inverse kinematics)

3. Dynamic specification uses
   A. key frames
   B. goals
   C. forces and torques with Newton's laws
   D. scripts only
   Answer: C. Gives realistic falling and collisions. (Key point: Dynamic)

4. In keyframe specification the computer produces
   A. key frames
   B. goals
   C. forces
   D. in-between frames by interpolation
   Answer: D. Animator defines key frames. (Key point: Keyframe)

## Related in Computer Graphics

- [Anti-aliasing methods in animation](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Aanti-aliasing-computer-animation) — Computer Graphics, chapter 1
- [Raster animation](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_graphics%3Araster-animation) — Computer Graphics, chapter 1

## Related in other subjects

- [Conceptual, specification, implementation model classification](https://www.bctengineer.com/question.md?key=semester_6%2Fobject_oriented_analysis_and_design%3Ahospital-conceptual-specification-implementation) — Object Oriented Analysis and Design, chapter 2