Photogate Launch
A ball rolls across a table and off the edge. Where will it hit the floor? If you know how fast the ball is moving when it leaves the table, you can make this prediction. In this lab you measure this “launch speed” with two photogates, predict the landing spot, and then put a target there and find out how close you got.
A photogate is an infrared beam across a small frame. The interface records the instant the beam is blocked, to within a few microseconds. With two gates a known distance apart, the time between the ball blocking the first beam and blocking the second gives its average speed between them.
What you need
Vernier LabQuest Mini (or LabQuest 2 or 3) connected by USB, and Chrome or Edge. Two Photogates. Put Gate A in DIG 1. Put Gate B in DIG 2, or plug it into the daisy-chain port on Gate A. A ramp and a steel ball or marble, a meter stick, a plumb bob, paper, and carbon paper.
- Put the gates on the table near its edge, with Gate B within a few centimeters of the edge. Line them up so the ball passes through the middle of each beam.
- Build a short ramp before Gate A and mark a release point on it. Release the ball from the same mark every time, so every roll has the same speed.
- Measure the gate spacing from beam to beam, and the table height from the floor to the tabletop.
Time several rolls and catch the ball each time it reaches the table edge. Once you have a consistent launch speed, work out where the ball will land, put a target there, and let the ball fly.
Photogate Launch
Time the ball through two photogates, then predict where it will land.
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