# Moving finger on TV screen produces a trace? **URL:** \ **Category:** Factual Questions\ **Created:** [May 13, 2016, 4:20pm UTC](https://boards.straightdope.com/t/moving-finger-on-tv-screen-produces-a-trace/754691 "2016-05-13T16:20:00Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [May 13, 2016, 4:20pm UTC](https://boards.straightdope.com/t/moving-finger-on-tv-screen-produces-a-trace/754691/1 "2016-05-13T16:20:00Z")
I have a new Sharp TV for the guest room. I noticed that our 3 year old grandson loves to follow objects on the screen with his finger. And this leaves a short lived “trace” that follows his movements. Today, he was doing the same thing except using a rounded plastic toy, and the traces were far longer. I tried it myself. Moving a finger about 2 inches per second leaves an inch long trace. Moving a plastic toy at the same speed leaves a 3 to 4 inch trace. I am not pressing hard, just touching. It is more obvious when I watch him do it, he leaves far longer traces than I do. But that may be the viewing angle. So what cause the traces? Dennis ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 13, 2016, 4:33pm UTC](https://boards.straightdope.com/t/moving-finger-on-tv-screen-produces-a-trace/754691/2 "2016-05-13T16:33:05Z")
You’re squashing the cells that hold the Liquid Crystal material. Even a tiny deformation changes the way they polarize the light, resulting in a visible trail. If you press hard enough, you will leave a “bruise” that will never go away. I would recommend keeping your grandson away from a good TV… ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [May 13, 2016, 5:01pm UTC](https://boards.straightdope.com/t/moving-finger-on-tv-screen-produces-a-trace/754691/3 "2016-05-13T17:01:32Z")
So if I was kidnapped I could leave a clue behind by writing on a TV with enough pressure. Dennis ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [May 13, 2016, 5:20pm UTC](https://boards.straightdope.com/t/moving-finger-on-tv-screen-produces-a-trace/754691/4 "2016-05-13T17:20:01Z")
> [@mixdenny](#): > > So if I was kidnapped I could leave a clue behind by writing on a TV with enough pressure. > > Dennis Yep. Almost all the TVs at my gym are “bruised.” The monkeys pushed on the screens when they were hanging them. It kills me to see that - all these nice, new flat-screen TVs that have big blotches on them, because people weren’t careful when hanging them. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [May 14, 2016, 9:18am UTC](https://boards.straightdope.com/t/moving-finger-on-tv-screen-produces-a-trace/754691/5 "2016-05-14T09:18:14Z")
> [@beowulff](#): > > I would recommend keeping your grandson away from a good TV… And away from any flat screen tv or other heavy thing (warddrobe, tallboy, bookshelf ,etc) that the child could pull down. Even if you think he is a good boy who doesn’t do such a thing …