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  • Date Submitted: 04/01/2012 03:01 AM
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Home >   Science Fair Project Ideas   > Background Info   > Science Interest Survey   >   Recommendations   > Measuring the Speed of Moving Objects with Stroboscopic Photography  
Measuring the Speed of Moving Objects with Stroboscopic Photography


A strobe light can illuminate an entire room in just tens of microseconds. Inexpensive strobe lights can flash up to 10 or 20 times per second. This project shows you how to use stroboscopic photography to analyze motion.

The goal of this experiment is to calibrate a variable-frequency strobe light and then use it to measure the speed of a ping pong ball (or some other moving object).


How do you "freeze" motion with your camera? The first answer that probably comes to mind is "Use a fast shutter speed." If the camera sensor (or film) is only exposed to light for a very short time, the moving object may appear still. It depends on how fast the image projected by the lens is moving and how long the shutter is open. What types of motion can you freeze with shutter speed alone? We can do some calculations to see.

Let's imagine that we're going to take a photo of a paper airplane. The airplane will be flying parallel to the camera's film plane. For this thought experiment we will be making several assumptions. We'll use numbers that will make it easy to generate a "rule of thumb" for motion blur. Let's assume that the airplane is moving at a speed of 1 m/s. Additionally, we'll assume that we've placed the camera so that the field of view will capture exactly 1 m of the airplane's flight path. Finally, we'll assume that we're using a 35 mm film camera, with a shutter speed of 1/1000 s.

How far will the airplane travel while the shutter is open?

1 m/s ×1/1000 s = 1/1000 m = 1 mm

How far will the image of the airplane travel on the film? For this calculation, we set up a proportion between...


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