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?

What would happen if it was played backwards?

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

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

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...


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.