{"id":3202,"date":"2010-05-18T09:38:21","date_gmt":"2010-05-18T14:38:21","guid":{"rendered":"http:\/\/brocku.ca\/brock-news\/?p=3202"},"modified":"2010-05-18T09:38:21","modified_gmt":"2010-05-18T14:38:21","slug":"media-talk-it%e2%80%99s-our-eyes-and-our-ears-playing-tricks-on-us","status":"publish","type":"post","link":"https:\/\/brocku.ca\/brock-news\/2010\/05\/media-talk-it%e2%80%99s-our-eyes-and-our-ears-playing-tricks-on-us\/","title":{"rendered":"Media Talk: It\u2019s our eyes and our ears playing tricks on us"},"content":{"rendered":"

In the St. Catharines Standard<\/em> \u201cSearch Engine\u201d column on May 8, Physics chair Edward Sternin explained why wheels on fast-moving vehicles seem to be going backward. The oddity is called the stroboscopic effect, he said.<\/p>\n

The rest of his response:<\/p>\n

Sternin explained in an email that light receptors in our retinas need about 30 milliseconds to detect light that comes into the eye and send the image to the brain.<\/p>\n

If the image changes faster \u2014 more than 30 to 40 times per second \u2014 we don’t notice it.<\/p>\n

Movies and TV programs rely on that inability to create an illusion of smooth motion from a sequence of snapshots.<\/p>\n

Sternin said if you were to slow down a movie and look at it frame-by-frame you would see the little jumps a moving object performs from one frame to the next.<\/p>\n

But when the same sequence passes in front of your eyes at the normal rate of 24-to-30 frames per second, your eyes and your brain perceive the sequence of flashes as one continuous motion.<\/p>\n

A rotating wheel is a special case.<\/p>\n

That’s because the motion is periodic, with the small markings on the side of the wheel repeating their position with every full turn.<\/p>\n

Sternin said if a wheel rotates exactly one full turn in the time it takes for the next frame to be captured, every shot in a sequence would look identical to the previous one \u2014 the wheel would look like it wasn’t moving at all.<\/p>\n

If the wheel rotates almost a full turn, such as from 12 o’clock to 9 o’clock, our brains don’t recognize it as a 3\/4 rotation forward but as a 1\/4 rotation backwards.<\/p>\n

This happens only at very high speeds, about 200 kilometres an hour, when wheels turn at the same rate as the frames of the TV, about 30 times per second.<\/p>\n

Sternin said the effect is easier to achieve in wheels with a repeat pattern, like four or five mounting bolts or six to eight spokes of the wheel in a wagon.<\/p><\/blockquote>\n","protected":false},"excerpt":{"rendered":"

In the St. Catharines Standard \u201cSearch Engine\u201d column on May 8, Physics chair Edward Sternin explained why wheels on fast-moving vehicles seem to be going backward. The oddity is called the stroboscopic effect, he said.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[6],"tags":[81],"_links":{"self":[{"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/posts\/3202"}],"collection":[{"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/comments?post=3202"}],"version-history":[{"count":1,"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/posts\/3202\/revisions"}],"predecessor-version":[{"id":3204,"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/posts\/3202\/revisions\/3204"}],"wp:attachment":[{"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/media?parent=3202"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/categories?post=3202"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/brocku.ca\/brock-news\/wp-json\/wp\/v2\/tags?post=3202"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}