Projectiles

Projectile Motion

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A projectile is any object that is cast, fired, flung, heaved, hurled, pitched, tossed, or thrown. (This is an informal definition.) The path of a projectile is called its trajectory. Some examples of projectiles include…

  • a baseball that has been pitched, batted, or thrown
  • a bullet the instant it exits the barrel of a gun or rifle
  • a bus driven off an uncompleted bridge
  • a moving airplane in the air with its engines and wings disabled
  • a runner in mid stride (since they momentarily lose contact with the ground)
  • the space shuttle or any other spacecraft after main engine cut off (MECO)

The force of primary importance acting on a projectile is gravity. This is not to say that other forces do not exist, just that their effect is minimal in comparison. A tossed helium-filled balloon is not normally considered a projectile as the drag and buoyant forces on it are as significant as the weight. Helium-filled balloons can’t be thrown long distances and don’t normally fall. In contrast, a crashing airplane would be considered a projectile. Even though the drag and buoyant forces acting on it are much greater in absolute terms than they are on the balloon, gravity is what really drives a crashing airplane. The normal amounts of drag and buoyancy just aren’t large enough to save the passengers on a doomed flight from an unfortunate end. A projectile is any object with an initial non-zero, horizontal velocity whose acceleration is due to gravity alone.

An essential characteristic of a projectile is that its future has already been preordained. Batters may apply “body English” after hitting a long ball, but they do so strictly for psychological reasons. No amount of leaning to one side will make a foul ball turn fair. Of course, the pilot of a disabled airplane may regain control before crashing and avert disaster, but then the airplane wouldn’t be a projectile anymore. An object ceases to be a projectile once any real effect is made to change its trajectory. The trajectory of a projectile is thus entirely determined the moment it satisfies the definition of a projectile.
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In projectile motion theory air resistance is negligible

Here is a video

An introduction to Projectile Motion. The main concepts are explained, in particular the independent treatment of the horizontal and the vertical motion

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