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 (3.6 mph = 1 meter per second).
Velocity could be anything up to Move. It might exceed Move when diving or falling.

An object in a collision inflicts dice of crushing damage equal to (HP x 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. 

• Small Piercing (pi-): Wounding Multiplier x 0.5
  A briar bush or a floor littered with small piercing objects like broken glass or caltrops.

• Piercing (pi): Wounding Multiplier x 1
  Falling onto a rot iron fence, a pit trap of sharpened bamboo stakes, or into splintered wood.

• Cutting (cut): Wounding Multiplier x1.5
  Impacting the edge of broken glass, sheer crystalline environments, or landing in a weapon rack full of sharp things.

• Impaling (imp): Wounding Multiplier x2
  Landing on jagged rock formations, spears, or larger wooden stakes.

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 . . .

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 meters. 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 {Hardness} x 10 {HP} x 19 {Velocity})/100 = 380/100 = 3.8d6, which rounds up to 4d crushing.

Hardness of Landing

The rigidity of the material you land can impact the damage you receive on collision with it.  This is done with a multiplier to the falling objects HP.
There are three categories of hardness for a landing:

• Soft (x0.5 HP): Liquids, jellies, and easily compressed objects such as Water, Slime, or Hay

• Normal (x1 HP): More standard materials like Dirt, Earth, or Clay, as well as trees or wood.

• Hard (x2 HP):  Truly rigid materials like Stone, Concrete, and Metal structures

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 meters/second. Use the low end for a spread-eagled fall, the high end for a swan dive. For dense objects (e.g., rocks) or stream-lined 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 below and calculate damage as for an ordinary collision. To hit someone with a dropped object, use the Dropping skill. Most dropped objects will have Acc 1. Your target cannot avoid the object unless they know it’s coming. If they're aware of it, it can be dodged.

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