## Wednesday, January 2, 2013

### Class 1 Week 4

Yay It's week 4! This week you'll be revising your bouncing ball based on your mentor's e-critique.
You will also get to animate..not one...but TWO bouncing balls! Next week it's three...not. :)

Before I give you the most important advice of your life (well...most important advice of the day? Hour? Well it's advice anyway...), here's a fun little video from Bill Nye:

We're gonna talk physics this week. I love physics. I almost became an engineer because I love physics. However, I stink at calculus...so yeah engineering didn't work out. But Physics still helps with animation!!!

So Bill Nye talked about momentum and gave a great visual image. A ping pong ball is simply too light to knock down blowing pins! So what does this mean for you this week? Well a lot of things!

I want to state one major thing about gravity next. There are a lot of misconceptions about gravity (and momentum too). First off I want to pose you this question:

If you drop a basketball ball and a medicine ball from the same height at the same time, which one will hit the ground first? A basketball weighs about 22 ounces. A medicine ball of the same size likely weighs around 8-15 lbs. Got your answer?

-Will the Basketball hit first because it's....lighter and uh, maybe gravity affects it differently?
-Or will the medicine ball hit the ground first because it's heavier?

It's gotta be the medicine ball right? I mean it's WAY heavier! Let's watch this video and find out:

Oh no! They hit the ground at the same time?! What does this mean? Well I'll do my best to explain.

Yes the medicine ball is much heavier. And because of that, the gravitational pull is greater on it. That doesn't mean it hits the ground first, it just means it hits the ground harder and loses more energy each bounce compared to the basketball.

However! The acceleration due to gravity is the same for ALL objects! Of course there is wind resistance, human error, drag, blah blah blah, so many things that can cause things to not hit the ground at the same time. In a perfect condition, everything hits at the same time (Would you believe me if I even told you in a perfect vacuum a feather and a bowling ball would hit at the same time? It's true!).

So what does this mean for animation? Well it means a few things.

1. Make sure you don't: drop the two balls from the same height, but then have the heavier one hit the ground a lot sooner.
2. There's a problem also...It just doesn't look right if the two object hit at the exact same moment.

“So Brandon, you're telling me that they have to hit at the same time, but if I do that it will look wrong?”

Kind of :) Unless you really nail the energy loss in the two balls, it will look wrong.

So here are some suggestions:

-Drop each ball from a different height and cheat that fall time just ever so slightly to trick the eyes into seeing the heavy ball drop faster. (Just a litte!)

-You could also drop each ball at a different time. Like maybe drop the light ball and have it come to a rest, then drop the heavy ball, which could cause the light ball to jump up a little bit from the shock of the heavy ball.

There are a bunch of ways you could go about it.

Lastly, I'll leave you with some film reference I put together. It's a 9 pound medicine ball vs a regular golf ball:

Now go have fun!
Happy Animating,
~Brandon