Mrs. VB -Projectile Motion - 2.) Types of Motion

Motion: Horizontal & Vertical

What is MOTION?

In physics, motion is the change in the position of an object over time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed, and time. We will first look at the 2 main types of motion, horizontal & vertical, then combine to learn about projectile motion! Lets remember the basics....

Horizontal Motion

The definition of horizontal motion is an object moving in the horizontal, or x, direction only. You can think of this as an object moving left or right and no up and down motion. The horizontal motion of an object is not concerned with the force of gravity. This means that the horizontal velocity is constant, even while the vertical velocity is accelerating. The reason is because perpendicular vectors act independently of each other.

An object projected at an angle to gravity can be broken into its horizontal and vertical components, which is basically what projectile motion is-the combination of horizontal and vertical motion, but we need to make sure we understand horizontal, and then next vertical. This horizontal velocity component is also unaffected by the force of gravity.

The horizontal velocity of an object moving in a given direction will remain constant provided there are no forces acting in that direction. A force perpendicular to the direction of motion may change the direction of the object but will have no effect on the velocity in the given direction.

This means that a horizontal velocity is independent of a vertical force or resulting velocity, such as caused by gravity.

In the illustration below, the initial velocity of the object (v_i) is the constant horizontal velocity (v_x). The velocity caused by gravity (v_g) is the velocity in the y-direction (v_y). The Earth is considered flat for short displacements.

Velocity from gravity is independent of initial horizontal velocity

Vertical Motion

Vertical motion is referred as the movement of the object against the gravitational pull. It is the motion that is perpendicular to the straight or flat surface. It can also be a straight upward and downward motion but the perfect vertical motion does not usually pursue a straight line path, that is what we will get into when we learn how to solve projectile problems.

In terms of the traditional coordinate plane, vertical motion is all motion in the "y" direction. Likewise, horizontal motion is all motion in the "x" direction.

Thoughtful questions on Motion

How is horizontal motion independent?
What happens when an object is projected perpendicular to gravity? (remember gravity is vertical)
Is horizontal velocity constant when an object is projected at a downward angle? (think...would there be any horizontal velocity?)
If an object has only horizontal motion can it move up and down?

Answers:

1.) It's not affected by vertical motion

2.) It's horizontal velocity remains the same but it falls according to gravity.

3.) Yes

4.) No

Motion: Horizontal & Vertical

Thoughtful questions on Motion

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