My new summer physics lab: Google’s nexuscontraption
The Google elves have been busy putting together a Rube Goldberg game that really is just a big add for their latest phone, but I prefer to think of it as my summer physics lab.
Experiment 1: How do objects fall in the Google lab?
This is a pretty basic experiment. Let’s just drop the ball, and record its motion using Tracker Video Analysis.
Note: if you closely examine this video, you’ll see places where the ball doesn’t seem to move between frames. I think this frame doubling is somehow an artifact of either the Flash animation or SnapzPro, but I’d appreciate any advice this matter.
Despite this, I decided to go ahead with the investigation, and produced this graph of the y-velocity of the ball vs time. One of the beautiful things about doing video analysis on video games is that the contrast is so high, Tracker can autotrack objects with tremendous ease.
So the ball seems to be falling with a constant acceleration of . The fact that that acceleration is constant gives us a good reason to make the assumption that the ball is only experiencing a constant gravitational force, and if we assume that it the force is due to the earth, whose gravitaitonal field causes objects to accelerate at , we can find the scale of the google physics lab.
The diameter of the ball is about 31 pixels, or about 0.51 m. Those are fairly large balls they’re dropping in the lab. No wonder they need robot claws.
Experiment 2: Exploring the properties of Google’s rubber bands
One of your primary tools for moving objects around in the game is to use rubber bands. Let’s see what we can find out about these rubber bands.
Here’s another video of the ball making 2 bounces on the rubber band.
And here’s the graph of the y-position of the ball as a function of time.
Here’s a graph of the speed of the ball versus time.
If we know the speed of the ball before and after the collision, we can calculate the coefficient of restitution (COR) which is defined as ratio fo the speed after the collision to the speed just preceeding the collision.
We can read these values in from the graph above.
This coefficient seems pretty high, since a golf ball hitting a hard surface has a COR of 0.86, but maybe Google has some very special rubber bands.
Experiment 3: Exploring the dynamics of forces exerted by rotating oscillators.
On the next level, you get access to fans, which turn out to be an idea tool for exploring forces. Let’s see how the balls move when under the influence of a fan.
There are two interesting features of this graph—near the beginning of the motion the graph is curved, which indicates that the velocity is increasing. Later, the graph becomes straight, indicating constant velocity, and that the airstream of the fan is no longer exerting a force on the ball.
We see the velocity of the ball is initially increasing at a constant rate of or —more than 3g! That’s a big acceleration. Does that mean the fans in the google world are very powerful, or that the balls have very little mass?
For now, I’ll stop here. But I do have more questions that I’m curious about:
- Can I find the spring constant of the rubber bands?
- Can I find the mass of the ball? Or at least compare its mass to the mass of a block?
- Can we find the coefficient of friction of the lab tables in the Google lab?