Physics in games
Game physics, as defined by Bluebird International. (n.d.) “refers to the set of rules and algorithms used to simulate the behavior of physical objects and movements within a video game environment”.
The American Physical Society (2023) identifies Trespasser (1998) as the first game to utilise a complete physics-based engine including ragdolls, describing its glitches as “disastrous”.

Figure 1. Trespasser 1998
Some helpful definitions
​A rigid body
According to Wikipedia (2024) a rigid body is “a solid body in which deformation is zero or negligible”.
“Rigidbodies allow your GameObjects to act under control of the physics engine” (Unity, 2024)
A ragdoll
Extended from this a ragdoll is a series of rigid bodies connected by a system of constraints. (Wikipedia, 2024)
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​In his GDC talk, Naughty Dog's Michal Mach (GDC 2025, 2019) identifies ragdoll physics as one of the most common example of physics in a game. According to Larksuite (n.d.) ragdoll physics “refers to a type of physics engine that simulates the behavior of limp bodies, mimicking the movements of a ragdoll.” Mach’s talk also describes some of the the basic elements of a ragdoll physics simulation.​​

Figure 2. Basic Physics Simulation GDC 2025 (2019)
The elbow
In a physics engine, actors are treated as a series of physics bodies connected by joints, each with tailored settings to customise their individual characteristics. These settings also define the relationships between the rigid bodies, such as through the joints. In a human, the elbow has a natural restriction of movement. It has the ability to flex in only one direction, and also an inability to rotate around it’s axis. If an elbow didn’t meet these constraints, we would likely consider that person in pain, or, if over-rotated enough, they would have a broken arm. These attached rigid body cylinders in the arm which representing the forearm and upper arm now need to understand their relationships through their associated settings. Without these constraints, the movement of the characterised person would look completely unnatural and broken to us as the player. The one-way rotation of the elbow joint would be a characteristic of hinge and joint settings in terms of a physics engine. The hinge would be limited to one axis and would be registered to the associated joint. (GDC 2025, 2019)
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In simple objects like as a cube or sphere that are set to be moving within a physics-based game, Bennett Foddy in his GDC 2025 talk (2018) highlights some core elements of physics in the engine that need to be controlled such as:
Gravity
Units
Timesteps
Collisions
Resolving constraints
Mass
Slowing down – adding custom drag forces
These elements are used in game to creates impressions such as the weight of an object, relative feeling of size and scale between game objects, buoyancy, responsiveness of interactions while minimising game breaking bugs GDC 2025 (2018).
In contrast, would be a system fully driven by animations. Animations are keyframed sequences which are playing through a series of preplanned movement stages. These stages of design are usually designed to look realistic, for example, a player running. However, there is no inertia added to the player at these points; the keyframes are being played through more like a video player. As such, the interactions of the animation to objects in game do not have physics and therefore cannot pass onto other elements in the games unless other objects in the game have physics-cased elements set up to respond in a way that appears appropriate in a game situation.
What are we using in games?
Common 3D physics engines in Unreal and Unity are:
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PhysX which is a realtime physics engine middleware developed by Nvidia (Wiki, n.d.)
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Havok
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Unreal’s Chaos Physics system
Chaos Physics is Unreal’s solution to provide users with a light-weight physics simulation system. As Epic (n.d.) states, “[w]hile using Chaos Physics, users should not notice much of a difference from PhysX while performing basic Physics simulations with Unreal Engine.”
These systems help developers interpret physics in the game without having to design a calculation-based system to characterise each of the items in the game. The simulation is generated through calculations within these engines based on its design.
These are just a few examples of the types of physics systems now included in Unreal Engine’s Chaos Physics system (Epic Games, n.d.) Each of these elements has precalculated behind-the-scenes algorithms to determine the reaction and interactions rules that govern the elements within the game space.
Just some of the time of physics systems in unreal
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Destruction
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Networked Physics
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Chaos Visual Debugger
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Rigid Body Dynamics
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Rigid Body Animation Nodes and Physical Animation
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Cloth Physics and Machine Learning Cloth Simulation
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Ragdoll Physics
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Vehicles
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Physics Fields
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Fluid Simulation
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Hair Physics
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Flesh Simulation
Lark Suite (n.d.) defines these solutions as a “software component that calculates and simulates the physical interactions and movements of objects within a game environment.” They handle the calculations for the some of the core elements of physics including: mass, gravity, drag forces, inertia, velocity, acceleration, rigid bodies and constraints.
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Bullet eg
Buttons you’ve probably pressed

References:
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American Physical Society. (2023). Video game incorporates physics. Available at: https://www.aps.org/apsnews/2023/09/video-game-incorporates-physics [Accessed 28 Oct. 2024].
Bluebird International. (n.d.). Game physics. Available at: https://bluebirdinternational.com/game-physics/ [Accessed 28 Oct. 2024].
Epic Games. (n.d.). Chaos physics overview. Available at: https://dev.epicgames.com/documentation/en-us/unreal-engine/chaos-physics-overview?application_version=4.27 [Accessed 28 Oct. 2024].
Epic Games. (n.d.). Physics in Unreal Engine. Available at: https://dev.epicgames.com/documentation/en-us/unreal-engine/physics-in-unreal-engine [Accessed 28 Oct. 2024].
GDC 2025 (2018). Designing with Physics: Bend the Physics Engine to Your Will. Available at: https://www.youtube.com/watch?v=NwPIoVW65pE [Accessed 28 Oct. 2024].
GDC 2025 (2019). Physics Animation in Uncharted 4: A Thief's End. Available at: https://www.youtube.com/watch?v=7S-_vuoKgR4&list=PLuGpfSZhKuAhNsVbghYb-8mDjGJ4zAsNr&index=10 [Accessed 28 Oct. 2024].
Lark Suite. (n.d.). Ragdoll physics. Available at: https://www.larksuite.com/en_us/topics/gaming-glossary/ragdoll-physics [Accessed 28 Oct. 2024].
Unity Technologies. (n.d.). Programming physics. Available at: https://unity.com/solutions/programming-physics [Accessed 28 Oct. 2024].
Unity Technologies (2014) Rigidbody. Available at: https://docs.unity3d.com/560/Documentation/Manual/class-Rigidbody.html (Accessed: 29 October 2024).
Wikipedia. (n.d.). PhysX. Available at: https://en.wikipedia.org/wiki/PhysX [Accessed 28 Oct. 2024].
Wikipedia (2024) Ragdoll physics. Available at: https://en.wikipedia.org/wiki/Ragdoll_physics (Accessed: 29 October 2024)
Wikipedia (2024) Rigid body. Available at: https://en.wikipedia.org/wiki/Rigid_body (Accessed: 29 October 2024).
JOES SECTION
As video games physics engines get more complex over time, so does the need for a game's sound design to compliment the deepening minutiae of a game's interactivity. Luckily, the parameters and information supplied to us by a physics engine can directly feed into information to alter in-game sound accordingly. (Sinclair, 2020)
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The use of physics-based parameters in procedural sound design allows for subtle real-time manipulations based on the players interaction with the game world, allowing for a deeper sense of immersion and interactivity within the game. (Marks, 2017) (Bridget, 2021)
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Anything that can roll, slide, collide, bend and break in a game is physics related, and can have its own corresponding sound from the information provided. Rather than creating an exhausting amount of individual audio files, implementing physics-engines to inform immersive sound design is much less time consuming. If you were to throw an item in a game, a sound designer could use several variables to create a suitable outcome for its sound upon impact. Using real-time parameters, an appropriate sound system could gauge the item size and throwing intensity and use real-time parameters - mass, velocity, and speed - to drive real-time effects such as pitch or volume. (Somberg, 2021)
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Figure 1: Unreal Engine demonstration of physics-based sound design in-game, with the foley work matching up accurately with the movements of the various objects. (Oosterhuis, 2024)
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​Figure 2 shows an example of progressively complicated Unreal Engine blueprints interpreting physics-based information to inform the sound output. From top to bottom: A simple object collision; the sound process of an object impacted by velocity and finally, the use of curves to implement a choice of three sounds according to impact. (Stevens & Raybould, 2016)
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Figure 2. (Stevens & Raybould, 2016, pp. 270-273)
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​One important, constantly used asset in video games is the doppler effect. In real life, when a fire engine passes you by, the pitch of the siren is higher approaching you then lower when moving away. This is because the sound waves are emitted more often when a vehicle is approaching you and vice versa. (Gunn, 2023)
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Figure 3: Simplified demonstration of the doppler effect. (BBC Bitesize, 2024)
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The doppler effect is so prominent that it is included as a built-in audio feature in both Unreal Engine and Unity, with people needing to find ways to implement it into different audio engines. Here is a demonstration of what Unreal Engine’s Doppler node does. Although it may have made sense to show off a vehicle moving, this demonstrates how the node approaches a sound – the song speeding up and slowing down depending on the player approaching/receding from the source. (Daichi Gamedev, 2022)
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Figure 4: Unreal Demonstration. (Daichi Gamedev, 2022)
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The implementation of physics-based audio can be used to make a game feel more real than ever before, but this does not mean a naturalistic, complete reflection of reality is always the end goal. Rather, an audio designer’s goal is to use these tools to emphasise what makes the game feel immersive and fun – to contextualise the player to the game world and ground them to the experience. (Filimowicz, 2019)
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Figure 5: In Super Mario Galaxy, several levels utilise a rolling ball. The speed Mario rolls directly effects the pace, pitch and instrumentation of the music. (Nintendo Movies, 2020)
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References:
BBC Bitesize (2024) The Doppler effect – The expanding Universe – Higher Physics Revision – BBC Bitesize. Available at: https://www.bbc.co.uk/bitesize/guides/zphppv4/revision/1 (Accessed 29 October 2024).
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Bridgett, R. (2021) Leading with Sound: proactive sound practices in video game development. New York: Focal Press. Available at: https://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=2664884 (Accessed: 29 October 2024).
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Daichi Gamedev (2022) Unreal Engine doppler sound node. Available at: https://youtu.be/dNXrAl35OUM (Accessed: 29 October 2024).
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Filimowicz, M (ed.) 2019, Foundations in Sound Design for Interactive Media : A Multidisciplinary Approach. Taylor & Francis Group, Oxford. Available from: ProQuest Ebook Central. (Accessed: 30 October 2024).
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Gunn, A. (2023) Why the simple Doppler effect is key to understanding our Universe | BBC Science Focus Magazine. Available at: https://www.sciencefocus.com/science/doppler-effect (Accessed: 29th October 2024).
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Marks, A. (2017) Aaron Marks’ complete guide to game audio: for composers, sound designers, musicians, and game developers. Third edition. Boca Raton: CRC Press. Available at: https://www.oreilly.com/library/view/-/9781317636182/ (Accessed: 29 October 2024).
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NintendoMovies (2020). Super Mario Galaxy: All Rolling Ball Galaxies – Youtube. Available at: https://youtu.be/N8-Tx_hJcfM (Accessed: 29 October 2024).
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Oosterhuis, J. (2024) Physics-Based Audio System | Unreal Engine and Wwise. 14 May. Available at: https://youtu.be/AgIJUve9xK8 (Accessed 29 October 2024).
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Sinclair, J.-L. (2020) Principles of game audio and sound design: sound design and audio implementation for interactive and immersive media. New York, NY: Routledge. Available at: https://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=2564460 (Accessed: October 29, 2024).
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Somberg, G. (ed.) (2021) Game audio programming 3: principles and practices. Boca Raton: CRC Press, Taylor & Francis Group.
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Stevens & Raybould (2016) Game Audio Implementation: A Practical Guise Using the Unreal Engine. Burlington, MA; Oxon: Focal Press.
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Examples
This section will briefly explore how three different games have leveraged physics-based audio to unique effects.
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The Legend of Zelda: Tears of the Kingdom (Nintendo, 2023) has been lauded for its physics system. Its new mechanic, the Ultra Hand, allows the player to freely combine elements into contraptions they can use to solve puzzles in a way that is unique to them.
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Developers had to ensure these user creations would sound appropriate in any given space. To this end, they employed raycasts for automatic parameter calculation (Dohta et al., 2024):

Figure 1: Presentation slide showcasing the use of automatic parameter calculation in The Legend of Zelda: Tears of the Kingdom (Dohta et al., 2024).
These raycasts ensured sounds were played back in a convincing manner in any given space. This system has several advantages in contrast to the classical approach of setting reverb ‘zones’ for distinct areas (Stevens & Raybould, 2015), such as automatically creating transition regions between two sonically different areas (e.g. a forest and a cave). In the case of Tears of the Kingdom, it allows any sound emitter to be aware of its surroundings and be played back in a sufficiently convincing manner.
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While key acoustic effects such as attenuation and occlusion are necessary inclusions to most games as a means to induce immersion and player expectation of sound playback, recent advances in processing power mean developers must now consider the degree of physical accuracy in audio as a design consideration as opposed to a technical one (Ekman, 2013).
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Gears of War 4 (Microsoft Studios, 2016) leveraged Microsoft’s Project Triton (Raghuvanshi & Snyder, 2014) to hypothetically simulate acoustics to a standard rivalling acoustic modelling software. In practise, historic sound design principles for games and movies held true in how fantastical sounds should behave and sound (Corey & Ochoa, 2002).

Figure 2: Table showing how sounds from Gears of War 4 would be in the real world (Raghuvanshi & Tennant, 2014).
Instead of applying a blanket pass on all sounds, Project Triton was used at different strengths for different sound categories (Raghuvanshi & Tennant, 2017). Its most noticeable use was on dialogue, as a means to strongly convey a sense of space.
Figure 3: Gameplay from Gears of War 4 showcasing Project Triton acoustics simulation applied onto dialogue (Raghuvanshi & Tennant, 2014).
Finally, physics-based audio should be considered not only from the perspective of the emitter, but also the listener. With a majority of gamers opting to use headphones as their playback device (Corsair Gaming, 2023), sound localisation has become both a technical necessity and a key gameplay element for certain genres.
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Conveying the location of a sound in three-dimensional space relies on a complex response function known as the head-related transfer function (HRTF) that models the localisation cues of human auditory perception (Beig et al., 2019). Individual ear shape “leads to variations in the filtering of the sound source spectrum amongst individuals” (Beig et al., 2019 p201), meaning generalised HRTFs, providing an average ear shape, are used.
However, several companies now offer the creation and use of a personalised HRTF, including Apple (Apple, 2024), and notably in the gaming space, Embody (Embody, n.d.), who recently came under scrutiny by gaming media for offering their services for Call of Duty: Black Ops 6 (IGN, 2024).

Figure 4: Headline from IGN article covering the Black Ops 6 personalised HRTF controversy (IGN, 2024).
​​Whether using a personalised HRTF can create a noticeable competitive advantage remains to be seen, but the rise of VR and associated demand for immersion could indicate that personalised HRTFs will one day become commonplace.
References:
Apple (2024) Listen with Personalised Spatial Audio for AirPods and Beats – Apple Support (UK) [Online]. Apple Support. Available from: <https://support.apple.com/en-gb/102596> [Accessed 29 October 2024].
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Beig, M., Kapralos, B., Collins, K. & Mirza-Babaei, P. (2019) An Introduction to Spatial Sound Rendering in Virtual Environments and Games. The Computer Games Journal, 8 (3–4) October, pp. 199–214.
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Corey, M. & Ochoa, G. (2002) The American Film Institute Desk Reference. DK Publishing (Dorling Kindersley).
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Corsair Gaming (2023) Headset vs Speakers: Which Is Best for Gaming? [Online]. Corsair.com. Available from: <https://www.corsair.com/uk/en/explorer/gamer/headsets/headset-vs-speakers/> [Accessed 29 October 2024].
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Dohta, T., Takayama, T. & Osada, J. (2024) Tunes of the Kingdom: Evolving Physics and Sounds for ‘the Legend of Zelda: Tears of the Kingdom’ [Online]. YouTube. Available from: <https://www.youtube.com/watch?v=N-dPDsLTrTE> [Accessed 29 October 2024].
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Ekman, I. (2013) On the Desire to Not Kill Your Players: Rethinking Sound in Pervasive and Mixed Reality Games. Foundations of Digital Games, January, pp. 142–149.
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Embody (n.d.) Embody [Online]. Embody. Available from: <https://embody.co/> [Accessed 29 October 2024].
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Gears of War 4 (2016) Microsoft Studios.
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IGN (2024) Call of Duty: Black Ops 6 Has Built-in Support for Better Audio Tech That Costs $20 for 5 Years [Online]. Ign.com. Available from: <https://www.ign.com/articles/call-of-duty-black-ops-6-has-built-in-support-for-better-audio-tech-that-costs-20-for-5-years> [Accessed 29 October 2024].
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Raghuvanshi, N. & Snyder, J. (2014) Parametric Wave Field Coding for Precomputed Sound Propagation. ACM Transactions on Graphics, 33 (4) July, pp. 1–11.
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Raghuvanshi, N. & Tennant, J. (2017) Gears of War 4, Project Triton: Pre-Computed Environmental Wave Acoustics [Online]. www.youtube.com. Available from: <https://www.youtube.com/watch?v=qCUEGvIgco8> [Accessed 29 October 2024].
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Stevens, R. & Raybould, D. (2015) Game Audio Implementation. CRC Press.
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The Legend of Zelda: Tears of the Kingdom (2023) Nintendo.