Write the text of your article here! EnlargeHalf-Life 2's gravity gun is capable of turning innocuous objects into weapons, as well as assisting in physics-based puzzlesSee also: Half-Life 2Valve Software's Half-Life 2 made significant use of physics in the game, powered by Havok physics engine. Although the player can pick up and throw objects early in the game, this ability is somewhat limited in scope. Around a quarter of the way through the game, the player acquires the gravity gun, properly named as the "zero-point energy field manipulator". Alyx Vance explains that the gravity gun is designed for handling hazardous materials, but is mostly used for heavy lifting. The gravity gun significantly increases the player's ability to manipulate objects in the game. Like most other weapons in the game, the gravity gun has two trigger functions. The primary trigger causes the gun to emit a small discharge which emits energy to the targeted object. The distance which the object is forced is dependent on its weight and distance from the gun. The secondary trigger attracts the targeted object to the gun and holds it in midair a few inches away, negating its weight and allowing the player to carry it with them. Using the secondary trigger again will drop the item, while the primary trigger will launch it with considerable force.
By combining these functions, players can use the gravity gun to scale barriers and obstacles, create cover against enemy characters, or launch the objects at enemy characters, causing them considerable damage. Certain types of objects, such as saw blades, fuel barrels and hydrogen tanks are intentionally designed by Valve to be used as gravity gun ammunition. The gravity gun, however, cannot manipulate heavier objects and enemy characters until the late stages of the game, when the device becomes temporarily infused with dark energy.
The gravity gun was very well received by critics, who considered it one of the defining features of Half-Life 2s entertainment value. Planet Half-Life calls the gravity gun "the next level in interactive gaming." Electronic Gaming Monthly describes Half-Life 2s gravity gun as the "thinking man's death tool," which lets players "toy with gravity to kill foes with everyday objects." Call of Duty series military adviser Hank Keirsey stated that "the weapon is not very practical". He does, however, discuss its historical precedents, further stating that "The ancients learned very early how to use gravity to their advantage — but this usually involved rolling rocks down hills or pouring boiling oil down the castle walls. Those that failed to respect gravity suffered."