Collisions and Falls

Collisions and Falls

When a moving object hits another object, this is a collision. Use the rules below for ramming attempts, accidental crashes, falls, and dropped objects.

Damage from Collisions

An object or person's Hit Points and velocity determine collision damage. Mass only matters indirectly: massive objects usually have high HP, but it would hurt more to collide with a locomotive than with a pillow of the same mass! HP take into account both mass and structural strength.

"Velocity" is how fast the character or object is moving in yards per second (2 mph = 1 yard per second). Velocity could be anything up to Move. It might exceed Move when diving or falling; see High-Speed Movement.

An object in a collision inflicts dice of crushing damage equal to (HP × velocity)/100. If this is less than 1d, treat fractions up to 0.25 as 1d-3, fractions up to 0.5 as 1d-2, and any larger fraction as 1d-1. Otherwise, round fractions of 0.5 or more up to a full die.

If an object is bullet-shaped, sharp, or spiked, it does half damage, but this damage is piercing, cutting, or impaling, rather than crushing.

Falling Velocity Table

Fall	Velocity	Fall	Velocity	Fall	Velocity	Fall	Velocity
1 yard	5	13-14 yards	17	35-37 yards	28	68-71 yards	39
2 yards	7	15 yards	18	38-39 yards	29	72-75 yards	40
3 yards	8	16-17 yards	19	40-42 yards	30	76-79 yards	41
4 yards	9	18-19 yards	20	43-45 yards	31	80-82 yards	42
5 yards	10	20-21 yards	21	46-48 yards	32	83-86 yards	43
6 yards	11	22-23 yards	22	49-51 yards	33	87-90 yards	44
7 yards	12	24-25 yards	23	52-54 yards	34	91-95 yards	45
8 yards	13	26-27 yards	24	55-57 yards	35	96-99 yards	46
9 yards	14	28-29 yards	25	58-61 yards	36	100-103 yards	47
10-11 yards	15	30-32 yards	26	62-64 yards	37	104-108 yards	48
12 yards	16	33-34 yards	27	65-67 yards	38	109-112 yards	49

Alternatively, calculate velocity in yards per second as the square root of (21.4 × g × distance fallen in yards), where g is the local gravity in Gs (g = 1 on Earth). Round to the nearest whole number.

Immovable Objects

If a moving object hits a stationary object that is too big to push aside – like the ground, a mountain, or an iceberg – it inflicts its usual collision damage on that object and on itself. If the obstacle is breakable, the moving object cannot inflict or take more damage than the obstacle's HP + DR.

Hard Objects: If the immovable object is hard, use twice the HP of the moving object to calculate damage. Clay, concrete, ordinary soil, and sand are all "hard," as is a building, mountain, or similar obstacle.

Soft Objects: If the immovable object is soft – e.g., forest litter, hay, swamp, or water – damage is normal. However, elastic objects (mattresses, nets, airbags, etc.) give extra DR against collision damage, ranging from DR 2 for a feather bed to DR 10 for a safety net, trampoline, or airbag. When striking water or a similar fluid, a successful Swimming roll (or vehicle control roll, if "ditching" a vehicle) means a clean dive that negates all damage. This roll is at a penalty for velocity; use the speed penalty from the Size and Speed/Range Table.

Hit Location from a Fall

If using hit locations, roll randomly for the hit location damaged in a fall. If the injury is to an extremity or a limb, do not ignore injury in excess of that required to cripple it. Instead, subtract the full amount from HP! If the fall would cripple a limb, roll 1d. On 5-6, all limbs of that type are crippled, although there is no extra injury.

Falling

A fall is a collision with an immovable object: the ground. Find your velocity when you hit using the Falling Velocity Table.

Example: Bill is pushed out a fifth-story window. He falls 17 yards. When he hits the street, his velocity is 19 yards/second. Bill has 10 HP, but he uses twice this because he hit a "hard" surface. Damage is (2 × 10 × 19)/100 = 3.8d, which rounds up to 4d crushing.

Falls and Armor: All armor, flexible or not (but not innate DR), counts as "flexible" for the purpose of calculating blunt trauma from falling damage. Thus, even if the victim has enough armor DR to stop the falling damage, he suffers 1 HP of injury per 5 points of falling damage. See Flexible Armor and Blunt Trauma.

Controlled Falls: If you are free to move, you can use Acrobatics skill to land properly. On a success, reduce falling distance by five yards when calculating velocity. If falling into water, you can do this or attempt a proper dive (see above) – decide which first!

Terminal Velocity: "Terminal velocity" is the maximum speed a falling object can achieve before air resistance negates further acceleration under gravity. Air resistance is relatively negligible for distances shown on the table, but increases drastically for longer falls.

Terminal velocity varies greatly by object. For human-shaped objects on Earth, it is 60-100 yards/second. Use the low end for a spread-eagled fall, the high end for a swan dive. For dense objects (e.g., rocks) or streamlined objects, it can be 200 yards/second or more!

The terminal velocity rules assume Earth-normal gravity (1G) and atmospheric pressure (1 atm.). Multiply terminal velocity by the square root of gravity in Gs. Then divide it by the square root of pressure in atm. Thus, gravity under 1G, or pressure above 1 atm., reduces terminal velocity; gravity over 1G, or pressure below 1 atm., increases it. Note that terminal velocity is unlimited in a vacuum!

Damage from Falling Objects

If an object falls on someone, find its velocity on the table above and calculate damage as for an ordinary collision. To hit someone with a dropped object, use Dropping skill. Most dropped objects will have Acc 1. Your target cannot avoid the object unless he knows it's coming. If he's aware of it, he can dodge.

A falling object with a Size Modifier equal to or greater than that of whoever it lands on impedes the victim's movement. He may move only one yard on his next turn, and his active defenses are -3. These penalties result from bulk, not mass, so ST is irrelevant.

Collision Angle

The angle at which you hit adjusts velocity, affecting damage. This is especially true in collisions between two moving objects!

Head-On: In a head-on collision between two moving objects, collision velocity is the sum of the objects' velocities. The slower object cannot inflict more dice of damage than the faster one.

Rear-End: If a faster object overtakes and strikes a slower one, collision velocity is that of the striking object minus that of the struck object. The struck object cannot inflict more dice of damage than the striking one.

Side-On Collisions and Falls: If a moving object strikes a stationary one, or strikes a moving object side-on, collision velocity is that of the striking or falling object. The struck object cannot inflict more dice of damage than the striking or falling one.

Example: A car with 60 HP, moving at 50 mph (velocity 25), strikes a pedestrian with 10 HP. The pedestrian was fleeing from the car at Move 5, so this is a "rear-end" collision. Collision velocity is 25 (car) - 5 (pedestrian) = 20. The car inflicts (60 × 20)/100 = 12d crushing damage on the pedestrian; the pedestrian inflicts (10 × 20)/100 = 2d crushing damage on the car.

Overruns

If the Size Modifier of the striking object in a collision exceeds that of the struck object by two or more (e.g., a car hitting a man) the striking object "overruns" the struck object. This inflicts additional crushing damage: roll thrust damage for ST equal to half the striking object's HP (or half its ST score, if it has one). Even a slow-moving elephant or a tank can crush someone who doesn't get out of the way. This rule does not apply to falls.

Anything with a ST attribute can deliberately trample as well; see Trampling.

Whiplash and Collision

Anyone inside an object that comes to a sudden stop in a fall or a collision (a falling elevator, a crashing car, etc.) takes damage. Find the speed lost in the "stop" and work out falling damage for this velocity. Seatbelts or straps give DR 5 vs. this damage; airbags give DR 10. In a collision involving an open vehicle, also work out knockback from this damage for those who weren't strapped in. This is how far they fly ...