Overview
This lesson introduces vertical projectile motion, focusing on objects moving vertically under the influence of gravity alone, and reviews key equations and concepts for analyzing their movement.
What is Vertical Projectile Motion?
- Motion occurs only in the vertical direction (up or down).
- A projectile is an object acted upon only by gravity (no engines or propulsion).
- Air resistance is ignored for grade 12 calculations.
Key Conditions and Equations
- Only gravity acts on the object, with a constant acceleration.
- The four equations of motion (for constant acceleration in a straight line) can be used.
- You seldom need the fourth equation; the main three suffice.
Acceleration Due to Gravity
- The acceleration for all vertical projectile problems on Earth is 9.8 m/s² downwards.
- The sign of velocity may change (upwards or downwards), but acceleration always points down.
- If an object is thrown upwards, velocity decreases by 9.8 m/s each second.
Example of Vertical Motion
- An object thrown upwards at 39.2 m/s will lose 9.8 m/s in speed each second until it reaches the top.
- After four seconds, the velocity reaches zero, then becomes negative as it falls back down.
- On other planets, the value for acceleration due to gravity changes (e.g., 1.4 m/s² on the Moon).
Velocity vs. Acceleration Direction
- Velocity and acceleration can be in opposite directions (e.g., object moving up but accelerating down).
- A decelerating car is an example: moving forward but slowing down due to acceleration acting backward.
Key Terms & Definitions
- Vertical — Movement strictly up or down.
- Projectile — An object only under the influence of gravity.
- Acceleration due to Gravity (g) — 9.8 m/s² downward on Earth.
- Equations of Motion — Formulas used when acceleration is constant and motion is in a straight line.
Action Items / Next Steps
- Memorize the value and direction of acceleration due to gravity (9.8 m/s² downward).
- Review and practice the three main equations of motion for vertical problems.