Script: Different Gravity in GURPS
Another video transcript, this time about gravity rules.
One might think that the rules for gravity only
come up in sci-fi games, but even D&D settings have environments with
different gravities. Spelljammers might travel in wildspace, and planar
travelers can travel to other planes of existence with stronger, weaker, or subjective
gravity. And some spellcasters and traps might change, reverse, or dispel
gravity as well. So, you might want to familiarize yourself with the gravity rules
in GURPS.
Most of the rules for different gravities can be found on page 350 of GURPS Basic Set. You will find that the rules are slightly different for low and high gravity. Gravity affects many things – encumbrance, movement, actions, and even attributes. You should also get used to the difference between mass and weight when playing in a game with different gravity levels. Everything I’m going to say here will assume that your native gravity is 1G, but you can proportionally scale everything for characters with other native gravities.
Let’s talk about encumbrance first. GURPS Basic Set says that if you are in a higher gravity, you should multiply your body weight and the weight of everything you are carrying by (local gravity in Gs) – 1, and treat it as extra weight you are carrying due to high gravity, which in turn will affect movement and skills. I should make an emphasis on body weight here – this is easy to miss here. These rules work well when your native gravity is 1G but give implausible results for anything else. GURPS Template Toolkit 2: Races says on page 15 that you should replace the multiplier with (local gravity in Gs – native gravity in Gs). This also means that a character with a native gravity of 0G will be encumbered by his entire body weight in any gravity.
When you are in a gravity less than 1G, multiply the weight of your gear by the local gravity to determine weight used for encumbrance. But I will come back to that later. As you can see, in this case, body weight does not matter – while your body weight does get reduced in a similar way, it does not affect your encumbrance.
In zero gravity, you weigh nothing, but you must push off from a solid surface to move. Your Move when doing so equals ST/2, rounded down. And since there’s no gravity, you will keep going at that speed until you grab or collide with something.
Local gravity also changes your normal jumping distance, throwing distance (but not damage!), terminal velocity of falls, and the diving acceleration for fliers.
How does gravity affect attributes? To explain that, I have to introduce the concept of a “G-Increment.” For a human, this is 0.2G unless he has the Improved G-Tolerance advantage which increases this increment.
Per two full G-Increments of higher gravity, you are at -1 to IQ, HT, and FP due to reduced blood flow to the brain, general fatigue, and cardiovascular stress.
Per each one full G-Increment of gravity difference, you are at -1 to DX, or at -1 per two full G-Increments, if you have the G-Experience advantage (p. B57)). This does not apply to all activities, but only to those that are related to agility and ballistics. So, Beam Weapons are not affected, Lockpicking is not affected, but Guns, Driving, and melee weapon skills are affected.
In zero gravity, your skills and DX rolls are affected as well. Whenever you are making a DX or DX-based roll in zero-gravity, your Free Fall skill acts as a cap. This does not apply when firing beam weapons (unless they have Recoil 2 or more) or operating vehicles or tools specifically designed for zero gravity (e.g., a spacecraft).
Pyramid #3-55 has expanded rules for using guns in other gravities on page 7, describing how gravity affects minimum ST, Recoil, and range, and also providing such tools as zero-G compensators and the Zero-G Shooting technique on page 11.
Finally, there is the Free Falling article from Pyramid #3-85 by Timothy Ponce. This article details the free fall and microgravity environments in much more detail – how your musculoskeletal and cardiovascular systems degenerate, how your spine might stretch, streamlined space adaptation syndrome rules, and how to recover from all these maladies.
This article also introduces a fix for encumbrance rules in different gravities. It says that weight adjusted by gravity only matters when determining how much someone can lift. All other rules, such as encumbrance, are based on mass, not weight. This is actually very important and I do not know why it wasn’t clarified in the Basic Set.
This article greatly expands the rules for activity and combat in microgravity and zero-G. First of all, how does it all work when there is no “down?” How does posture work? How falling or being knocked down works?
Now there are only two general “postures” – end-on and full-on. Falling, knockdown, and other similar things have been replaced by the loss of control. Such events occasionally require control rolls – rolls or Quick Contests against Free Fall. Failure results in loss of control over your movement – you suffer a DX penalty equal to your margin of failure, cannot alter your course, and continue at the same speed in the same direction you were moving. To regain control, you may roll every second against the higher of DX or a grappling skill to grab a nearby stable object. If successful, you can take a Ready maneuver to remove -1 of the control penalty. If you cannot grab anything, you may roll against Free Fall to remove -1 in penalties, but a failure will increase the penalty by your margin of failure! Alternatively, you may roll against Astrobatics to remove all penalties as a single Ready maneuver. Failure increases the control loss penalties as Free Fall. Body Sense acts as a complimentary skill.
New rules for working in free fall are introduced – time required to anchor yourself to a stable surface and effects that arise from this. Plus, now if you are unanchored, you can only bring half your ST to bear on any task, which seems reasonable.
Rules for moving and attacking in zero-G have been expanded. Propelling yourself by throwing items in the opposite direction is now described mechanically. Most attacks now require control rolls. Melee thrusting attacks give a bonus, and swung attacks impose a penalty. Any attacks that might cause knockback now automatically deal halved knockback that is applied to both the defender and the attacker. Guns now also require Free Fall rolls to avoid doubling the Recoil. I’m not sure how these rules interact with the gun rules from Pyramid #3-55. You should probably use either one or the other.
And, of course, there are new advantage enhancements related to zero-G, notes for existing skills, reworked mechanics for some existing techniques, and new techniques – Astrobatic Recovery and Free Fall Training.
And that’s it. As you can see, the gravity rules are quite complex, especially for microgravity and zero-G, but they add a new dimension to your game, sometimes literally, and can be fun to play around with. Thank you for watching, and I’ll see you next time!
Most of the rules for different gravities can be found on page 350 of GURPS Basic Set. You will find that the rules are slightly different for low and high gravity. Gravity affects many things – encumbrance, movement, actions, and even attributes. You should also get used to the difference between mass and weight when playing in a game with different gravity levels. Everything I’m going to say here will assume that your native gravity is 1G, but you can proportionally scale everything for characters with other native gravities.
Let’s talk about encumbrance first. GURPS Basic Set says that if you are in a higher gravity, you should multiply your body weight and the weight of everything you are carrying by (local gravity in Gs) – 1, and treat it as extra weight you are carrying due to high gravity, which in turn will affect movement and skills. I should make an emphasis on body weight here – this is easy to miss here. These rules work well when your native gravity is 1G but give implausible results for anything else. GURPS Template Toolkit 2: Races says on page 15 that you should replace the multiplier with (local gravity in Gs – native gravity in Gs). This also means that a character with a native gravity of 0G will be encumbered by his entire body weight in any gravity.
When you are in a gravity less than 1G, multiply the weight of your gear by the local gravity to determine weight used for encumbrance. But I will come back to that later. As you can see, in this case, body weight does not matter – while your body weight does get reduced in a similar way, it does not affect your encumbrance.
In zero gravity, you weigh nothing, but you must push off from a solid surface to move. Your Move when doing so equals ST/2, rounded down. And since there’s no gravity, you will keep going at that speed until you grab or collide with something.
Local gravity also changes your normal jumping distance, throwing distance (but not damage!), terminal velocity of falls, and the diving acceleration for fliers.
How does gravity affect attributes? To explain that, I have to introduce the concept of a “G-Increment.” For a human, this is 0.2G unless he has the Improved G-Tolerance advantage which increases this increment.
Per two full G-Increments of higher gravity, you are at -1 to IQ, HT, and FP due to reduced blood flow to the brain, general fatigue, and cardiovascular stress.
Per each one full G-Increment of gravity difference, you are at -1 to DX, or at -1 per two full G-Increments, if you have the G-Experience advantage (p. B57)). This does not apply to all activities, but only to those that are related to agility and ballistics. So, Beam Weapons are not affected, Lockpicking is not affected, but Guns, Driving, and melee weapon skills are affected.
In zero gravity, your skills and DX rolls are affected as well. Whenever you are making a DX or DX-based roll in zero-gravity, your Free Fall skill acts as a cap. This does not apply when firing beam weapons (unless they have Recoil 2 or more) or operating vehicles or tools specifically designed for zero gravity (e.g., a spacecraft).
Pyramid #3-55 has expanded rules for using guns in other gravities on page 7, describing how gravity affects minimum ST, Recoil, and range, and also providing such tools as zero-G compensators and the Zero-G Shooting technique on page 11.
Finally, there is the Free Falling article from Pyramid #3-85 by Timothy Ponce. This article details the free fall and microgravity environments in much more detail – how your musculoskeletal and cardiovascular systems degenerate, how your spine might stretch, streamlined space adaptation syndrome rules, and how to recover from all these maladies.
This article also introduces a fix for encumbrance rules in different gravities. It says that weight adjusted by gravity only matters when determining how much someone can lift. All other rules, such as encumbrance, are based on mass, not weight. This is actually very important and I do not know why it wasn’t clarified in the Basic Set.
This article greatly expands the rules for activity and combat in microgravity and zero-G. First of all, how does it all work when there is no “down?” How does posture work? How falling or being knocked down works?
Now there are only two general “postures” – end-on and full-on. Falling, knockdown, and other similar things have been replaced by the loss of control. Such events occasionally require control rolls – rolls or Quick Contests against Free Fall. Failure results in loss of control over your movement – you suffer a DX penalty equal to your margin of failure, cannot alter your course, and continue at the same speed in the same direction you were moving. To regain control, you may roll every second against the higher of DX or a grappling skill to grab a nearby stable object. If successful, you can take a Ready maneuver to remove -1 of the control penalty. If you cannot grab anything, you may roll against Free Fall to remove -1 in penalties, but a failure will increase the penalty by your margin of failure! Alternatively, you may roll against Astrobatics to remove all penalties as a single Ready maneuver. Failure increases the control loss penalties as Free Fall. Body Sense acts as a complimentary skill.
New rules for working in free fall are introduced – time required to anchor yourself to a stable surface and effects that arise from this. Plus, now if you are unanchored, you can only bring half your ST to bear on any task, which seems reasonable.
Rules for moving and attacking in zero-G have been expanded. Propelling yourself by throwing items in the opposite direction is now described mechanically. Most attacks now require control rolls. Melee thrusting attacks give a bonus, and swung attacks impose a penalty. Any attacks that might cause knockback now automatically deal halved knockback that is applied to both the defender and the attacker. Guns now also require Free Fall rolls to avoid doubling the Recoil. I’m not sure how these rules interact with the gun rules from Pyramid #3-55. You should probably use either one or the other.
And, of course, there are new advantage enhancements related to zero-G, notes for existing skills, reworked mechanics for some existing techniques, and new techniques – Astrobatic Recovery and Free Fall Training.
And that’s it. As you can see, the gravity rules are quite complex, especially for microgravity and zero-G, but they add a new dimension to your game, sometimes literally, and can be fun to play around with. Thank you for watching, and I’ll see you next time!
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