Projectile — Science definition

An object moving through the air acted on only by gravity after its launch (air resistance neglected).

Where it is taught

In use

A projectile is an object whose modeled post-release motion is governed by gravity alone.

Projectile & Two-Dimensional Motion

Questions using projectile

Problem 1

Ignoring air resistance, the horizontal velocity of a projectile during its flight…
  1. decreases to zero
  2. depends on the object's weight
  3. increases as it falls
  4. stays constant
Answer and explanation

stays constant

With no horizontal force acting, Newton's first law keeps the horizontal velocity constant for the whole flight.

Problem 2

At the top of a nonvertical projectile path, is total velocity zero?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. Vertical velocity is momentarily zero, but horizontal velocity remains nonzero without drag.

Problem 3

During a projectile's flight (ignoring air resistance), its vertical acceleration is…
  1. 9.8 m/s² downward
  2. increasing with speed
  3. zero
  4. dependent on its horizontal velocity
Answer and explanation

9.8 m/s² downward

The vertical motion is free fall, so the acceleration is a constant 9.8 m/s² downward the entire flight.

Problem 4

Explain what is meant by the 'independence' of a projectile's horizontal and vertical motions.
Answer and explanation

It means the horizontal motion and the vertical motion happen separately and don't affect each other's timing. Gravity only changes the vertical motion, pulling the object down at g, while the horizontal velocity stays constant because no horizontal force acts. The two motions share only the time in the air, so you can solve each as its own one-dimensional problem — the horizontal speed has no effect on how long the object takes to fall.

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