Wednesday, 30 September 2009

Negative times negative

Came across a few posts asking for a concrete explanation why negative x negative = positive.



Whenever I'm doing this with my kids i tend to show them videos.

This video, shows a man walking forwards (in a rather silly fashion...). When played forwards, which way does he go?
video



What would happen if it was played backwards?

video


This is a video of a (sadly now deceased) man walking backwards... If i play it forwards what way does he travel?

video



What would happen if i play the same video backwards? He moonwalks forwards!

video



So the first vid is walk forwards (+) * played forwards (+),

the second is walk fwd (+) * played backwards (-)


The third vid is walk backwards (-) * played forwards (+),

the last one is walk backwards (-) * played backwards (-)


This then leads to obvious questions like "right, MJ moonwalks 6 steps, how far and what way would he go if i play that vid backwards 5 times?" - then do it - play it back 5 times and count where the dude goes..

The nice thing about this is it allows me to cue massive moonwalk practise for my classes...


4 comments:

Teakay said...

That's brilliant. I'll remember that and use it when I have to teach my low ability year 7s about directed numbers!

Ryan said...

Glad you like it sir!
If it's any use to you let me know and i can drop send you the 4 video clips.

Teakay said...

That would be great!

Ryan said...

Cool. Drop me an email i'll send it off to you.