If I were to make up my own definitions (which apparently I like to do), I give the following:
- Model: This is some type of representation (conceptual, mathematical, physical, computational) of a real object. Example: a model of a bouncing ball would produce results that agree with a real bouncing ball.
- Animation: An animation is just like a model that has a visual representation. However, there is one big difference. An animation might not agree with real data. Perhaps the animation just displays some aspect of real life but is clearly not realistic in some way.
I guess you could say that a model isn’t completely realistic either. How about this, an animation can be used to tell a story and a model is used to do some SCIENCE? I like that.
I really don’t want to talk about models vs. animations. Instead, I want to show you somethings. I created some animations of a bouncing ball. Which one do you like the best?
Which one do you like the best? Which one do you think is the most realistic? Ok, you could argue that none of them are realistic since it keeps bouncing to the same height.
Instead of telling you how each ball bounces, here is a plot of the vertical motion as a function of time for the three balls.
From this plot it’s pretty easy to see that Ball A just moves at a constant speed and bounces back when it hits the ground. But what’s the difference between the other two balls? If you just look at the plot, it sort of seems like they just have different accelerations – but that’s not true.
Maybe it would be easier to see the difference with a plot of the vertical velocity. Here is that plot for all the balls.
Here you might be able to tell what I did for these three ball bounces. But just in case, I will give a brief description.
- Ball A: This ball moves down at a constant speed. When it gets to the floor, the ball changes direction and then moves up. I picked a ball speed so that it would take about the same bounce time as Ball B.
- Ball B: In this case, the ball falls with a constant acceleration (-9.8 m/s2). When the ball hits the ground, the velocity changes so that it is moving upwards. This is essentially a realistic ball bounce except that there is no loss of mechanical energy.
- Ball C: I like to refer to Ball C as my artistic masterpiece. Yes, it’s art. Look at the velocity graph. The slope of a velocity-time graph is the acceleration. What happens when the ball gets near the top of its path? Yes, the acceleration decreases. Why? Well, this gives the feeling of a ball just “hanging there at the top”. It’s like the Michael Jordan of bouncing balls. You look at that ball and think “Damn! That ball’s just flying there!” Yup, that’s what art does. It makes you think things like that.
Ok, so what’s the point of all this? Well, in an animation you sometimes don’t want things to be realistic. The end.