What is Projectile Motion?

A projectile is any object that is thrown, kicked, or launched into the air. Once it leaves your hand (or the launcher), the only forces acting on it are:

1. Gravity (pulling it down).
2. Air Resistance (slowing it down slightly—though usually, in physics class, we pretend this doesn't exist to keep the math easy!).

The path the object follows is called a trajectory, and it is always shaped like a curve called a parabola.

Key Variables

The Big Secret: Two Motions at Once

To understand projectile motion, you have to realize that the object is actually doing two completely different things at the same time.

Imagine we launch a ball from a cannon:

1. Horizontal Motion (Side-to-Side): The ball moves forward. Because gravity only pulls down, nothing is pulling the ball backward or pushing it forward once it's launched. So, it keeps moving at a constant speed sideways.
2. Vertical Motion (Up-and-Down): The ball moves up and then down. Gravity is the boss here. It slows the ball down as it goes up, stops it for a split second at the very top, and then speeds it up as it falls back down.

The Equations (The Math Behind the Launch)

For your STEM kit, you might want to predict where your projectile will land. We use different equations for the horizontal and vertical parts because they behave differently.

1. Horizontal Motion (The "Easy" Part)

Since gravity doesn't mess with horizontal movement, the speed stays constant.

2. Vertical Motion (The "Gravity" Part)

This is where gravity (g) comes in. The object accelerates downwards.

Try It: Interactive Simulator

Adjust the angle and velocity to see how the trajectory changes. Notice how 45° gives you the maximum range!

STEM Kit Challenge: The 45° Rule

When you are using your launcher, you will notice that the angle makes a huge difference.

• Launch straight up (90°): It goes high but lands right back on the launcher. (Horizontal distance = 0).
• Launch flat (0°): It hits the ground very quickly.
• Launch at 45°: This is usually the "Goldilocks" angle. In a vacuum, 45° gives you the maximum possible distance.

Real World Connections