Slow-Motion Ball Drop for Gravity Measurement — $10 (4 spots, need diverse locations!)

We are measuring gravitational acceleration (g) from around the world using slow-motion ball drop videos. We already have data from Pakistan, Poland, Ecuador, Argentina, and Belgium — now we need 4 more locations to complete our study.

INSTRUCTIONS:

1. Set your phone to slow-motion mode (240fps preferred, 120fps also works)
2. Use a well-lit room with bright overhead lights or natural daylight
3. Use a tennis ball or any round ball (standard tennis ball is 6.7 cm diameter, ideal for calibration)
4. Drop the ball from at least 1.5 meters against a plain wall (solid color, no patterns)
5. Release from rest — open your hand, do not throw
6. Keep camera steady and perpendicular to the drop path
7. Record at least 5 separate drops in one continuous video
8. Tell us your exact city and country when you submit

DELIVERY: Share a Google Drive or Dropbox link to the video within 2 hours of acceptance.

PRIORITY LOCATIONS (we need geographic diversity):

• India, Sri Lanka, or Southeast Asia
• Africa (South Africa, Kenya, Nigeria, etc.)
• North America (USA, Canada, Mexico)
• East Asia (China, Japan, Korea)
• Any location NOT already covered above

This is for a real physics paper. Thank you for contributing to science!