What “acceleration due to gravity” means
Downward is positive in this lab. With no air resistance, every object at one location has the same acceleration.
1. Gravity changes velocity
On Earth, an object's downward velocity increases by about 9.81 m/s during every second of free fall.
velocity = initial velocity + gravity × time
2. Distance grows faster each second
Because the object is continually speeding up, equal time intervals contain larger displacements.
distance fallen = initial velocity × time + ½ × gravity × time²
3. Mass does not set vacuum fall rate
A hammer and feather share the same acceleration on the Moon because no atmosphere produces drag.
4. Air resistance changes net acceleration
Drag grows with speed and acts upward. A skydiver approaches terminal velocity when drag balances weight.
Learning objectives
- Interpret gravity as a rate of velocity change.
- Connect constant acceleration to linear velocity–time graphs.
- Predict fall time and impact speed.
- Explain why mass does not affect vacuum free fall.
- Distinguish ideal free fall from motion with air drag.
Suggested experiments
- Compare identical drops on Earth, Moon and Mars.
- Use Moon hammer and feather, then add artificial drag.
- Give an upward initial velocity and watch velocity pass through zero.
- Increase skydiver drag and observe terminal velocity.