Intro to the wagon-wheel effect. Optical illusions, part 2

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Question 1: Is perception always equal to reality?

• No

• Yes

Answer explanation

No. An optical illusion is when our perception of what we see is different than reality.

Can something look still, when in reality it is rotating fast?

• No

• Yes

Answer explanation

Yes. This is called the wagon-wheel effect.

Could we get hurt if we always assume that objects that appear to be rotating slowly, are truly rotating quickly? 

• No

• Yes

Answer explanation

Yes. That wrong assumption could lead to a serious injury or even kill someone.

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NGSS.MS-PS3-5

Is a video a collection of still photos?

• No

• Yes

Answer explanation

Yes. When they are played quickly, we get the illusion of motion. 

With a slow shutter speed (e.g., 1/50), would we expect to prevent motion blur?

• No

• Yes

Answer explanation

No. A fast shutter speed (e.g., 1/500) will prevent motion blur. 

Is a typical frame rate 100 photos per second?

• No

• Yes

Answer explanation

 No. It’s about 30 photos per second. 

In the wagon-wheel effect, can we see a wheel’s spokes appear to rotate forwards slower than it is actually rotating?

• No

• Yes

Answer explanation

Yes. It could also look still or appear to rotate backward slowly.

Can we experience the wagon-wheel effect outside (without a video camera or fluorescent lights)?

• No

• Yes

Answer explanation

Yes. Our brains do this, though the exact method is unclear.