Describing Projectile Motion


Projectile motion allows us to predict and describe the motion of objects when propelled into the air. Whether this be a soccer ball kicked across a soccer field or a rock shot with a sling shot.

Projectiles travel through a parabolic arc, this is seen in the above picture. This path is due to an object have only one force acting on it after being launched. That is only gravity is pulling this projectile down, causing it to have a constant downward acceleration. The velocity of the object is constant in the x direction since there are no forces acting on it.

The assumptions we make with projectile motion include:

  • Gravitational field strength is constant and all of our scenarios are within this gravitational field.
  • The acceleration due to gravity on earth is 9.81 ms^-1, note this value changes slightly where we are on earth, however, we also assume this to be constant.
  • We assume air resistance is negligible.


Projectile motion is when a projectile follows a parabolic arc due to constant gravity pulling the object down and we assume air resistance to be negligible.


Question 1.

What conditions does an object require when in projectile motion?

Question 2.

What forces act on a projectile while it is in motion?

Question 3.

What are the assumptions we make with our projectile motion equation?

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