Gravity & Motion  (Newton's Law of Gravitation):

Objectives:

1.    Given a vector, resolve it into vertical and vertical components.

2.    For a projectile, describe the changes in the horizontal and vertical components of its velocity, when air resistance is negligible.

3.    Explain projectile motion.

Key Terms:

component    resolution    projectile

Web Resources:

Notes:

Projectile Motion:

Whenever an object is thrown in the air, it becomes a projectile.  Projectile motion is always a curve near the surface of the Earth.  There are two forces acting on every projectile.  The projectile moves forward due to inertia and accelerates downward due to gravity.  Although it sounds complicated, the path of the projectile can be simply be split into its horizontal and vertical components. Vertical Component

The vertical component can be solved using the formulas a = v/t, d = 1/2gt2, and v = gt.  The time that the ball takes in the above example is roughly 4 seconds. (Gravity rounded to 10 m/s)  This can be solved by splitting the journey in half then doubling the answer.

v = gt

t = (20m/s) / (9.8m/s2) ~ 2s    (This represents the first half of the journey.)

The distance can now be solved the same way using the formula d = 1/2gt2

d = 1/2gt2

d = 0.5*9.8m/s2*22 ~ 20m    (This again represents the first half of the journey.)

You will notice each side of the example is a mirror image of the other side.  What this means is that the initial velocity is the same as the end velocity and that at the midpoint the vertical velocity is equal to zero.

Horizontal Component:

Since there is no acceleration in the horizontal direction, distance can be simply be solved by using the formula d = vt.  (If given the horizontal component of the velocity.)  It is also important to note that in the absence of air resistance that the horizontally moving object travels a constant velocity.