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How to stop a mixer with light.

Light: Demonstrating stopping motion with a rapidly blinking light

Sunshine State Standards: SC.B.1.2 SC.H.1.2 SC.H.2.2

Materials:

• Mixer with variable speed and paddle with painted neon color
• Strobe light

To Know:
A rapidly blinking (strobe) light will make motion appear to stop if the speed of the light is synchronized with the speed of the moving object. Your eyes see the image
clearly only at the moment of the quick, bright flash so only that instant image is “seen” in your mind.

To Do and Notice:

• First set up and plug in the mixer and the strobe light into the outlet.
• A variable speed mixer will allow you to select a slow speed
• Notice that only one blade of the mixer paddle is painted neon.
• Set the mixer to run at the slowest speed.
• A strobe light has a knob, which can be turned to adjust the speed of the flashing light from the strobe.
• Point the strobe light at the mixer and slowly turn the knob to increase the flash rate of the strobe.
• You will notice that the mixer paddle seems to slow and then almost stop as you increase the flash rate.
• As you continue to increase the speed of the light, the mixer paddle will then appear to reverse its direction.

What’s Happening?

• The strobe light creates a very quick, instant flash of light that illuminates the mixer paddle. As the rate of the flash of light approaches the same rate of speed of the paddle your eyes see the neon paddle once per rotation of the paddle.
• As the strobe flash exactly matches the rotation rate, the paddle appears to have stopped because you always see it at the same point in its rotation.
• When you increase the speed of the flash, the paddle appears to reverse its direction because you see the paddle a fraction of a second earlier each time. This will give the paddle the appearance of slowly going backwards.

Learn more…

Developed by the GE Volunteers in partnership with the Museum of Arts and Sciences (MOAS) – Daytona Beach, FL