Science Fiction-Inspired Educational Resources for Teaching About Gravity!
Hi!
Man, someone is mowing their lawn outside and it feels like SUMMER! I’m excited. I’ve been watching a lot of scifi recently, and I thought I’d send out some of my favorite scifi-inspired gravity resources. You’ll find them below!
Here’s a quick summary of what I’ve got for you today:
Some examples from movies, video games, and science fiction novel scenes that illustrate gravity concepts super well
An artificial gravity activity
An inverse-square law activity for conceptualizing the math of gravitational fields
A gravity-measuring activity
I know a lot of you are teachers, and you already know a lot about what I’m sharing, but I’m going to start from the beginning so that these resources are hopefully useful to everyone. Feel free, as always, to take what’s useful and leave the rest!
I’m currently working on a second edition of the Newton’s Laws fairy tale, with a ton of new illustrations. Here’s a little entropy example, feel free to use this with your students:
(Entropy is a measure of orderliness in the universe. There are more disorderly states than orderly states, so when left to their own devices, things tend towards disorder!)
Anyway, let me know if you have any questions about anything I’m sharing here today. Feel free to pass anything along, and let me know if there’s anything I can do to help!
I hope you’re having a great week so far. Thanks as always for coming along.
All the best,
Sarah
Scientist Spotlight
This is Dr Nergis Mavalvala. She’s a professor of Astrophysics at MIT and the dean of the school of science. She was part of the team that first discovered gravitational waves, which she’s been studying since 1991. She also works on quantum measurement science, including quantum states of light. She’s Pakistani American and she and her wife live in Cambridge, Massachusetts with their two kids.
Some quotes from interviews she’s given:
"I grew up in a family where the stereotypical gender roles were not really observed. So I grew up thinking women can, must and should do anything and everything. That is very important for me."
"When everyone has access to education that's when all the other things come into place... [You've] got to do what gives you pleasure, gotta find a way to do it. People should just do what they enjoy most and I think for all of society whether it's in Pakistan or elsewhere we have to create opportunities for young girls to do what they're good at and do what they love to do must cultivate the sense of wonder in a child."
The Basics: What is Gravity?
Gravity is the force that causes things to fall. It’s the attraction that all mass has for all other mass. If you hold up two pencils, they’re actually pulling towards each other a teeny tiny bit. (Way too little for us to be able to feel it, though.)
So, technically, when you drop something, that object is being pulled towards the Earth (and the Earth is being pulled towards that object a bit, too.)
Gravity is a very weak force. We only notice it when objects are gigantic, like planets. The more mass something has, the more gravity it has.
If you were standing on the moon, you’d feel gravity, like you do here on Earth, but the moon is much smaller, so you’d only feel about 1/6th of the pull that you do here.
Gravity also gets weaker as you get farther away. So, if you were out in space, you might experience some of the pull of the Earth’s gravity, but it would be less the farther you got away from Earth.
A Gravity-Measuring Activity
Whenever I’m teaching a physics concept, I start with two things: 1. Embodiment, and 2. Relevance. In order for physics concepts to make sense, and to be more than just random things we’re memorizing, we need to feel them in our bodies, and we need to see why they might matter. This activity does both of those things.
Embodiment:
Go ride some swings. Have students pump up as high as they can and then just swing back and forth. What do they feel at various parts of their swing? Do they feel the push of the swing underneath them? Where is it the most? (We feel the push of the swing, and we feel when our speed changes, but gravity is always constant and always pointing down, which is a weird thing to realize, because it doesn’t feel like that because it gets wrapped up in so many other sensations.)
You can tell them that when they’re swinging without pumping, they’re something called a pendulum. Although, in this case, technically they’re a damped pendulum, because friction is slowing them down (their swings get less and less high every time). Damping is when an oscillation is losing energy, usually because of friction.
Relevance:
First thing: grab the book Hail Mary by Andy Weir and read the first scene.
The main character wakes up with no memories, in a room where the gravity feels slightly off. He doesn’t know where he is, or what he’s doing there, or even if he’s on Earth anymore. He makes a pendulum and uses it to measure the gravity, which tells him he’s not on Earth.
This is a genius scene, because measuring gravity is something anyone can do, with something as simply as a pendant necklace. It also establishes relevance. Sure, how likely is it that any of us will wake up with no memories but suspect we’re on a different planet? Not very, but it feels good to be prepared.
Math:
Have kids measure the actual strength of gravity on their own. You can do this in a few ways.
Easy way:
Cut a string that’s 1 m long
Tie a weight to the end
Set it swinging, and measure the time it takes to make a full swing (there and back)
That time is called the period of a swing.
The awesome thing about pendulums is that the period of a pendulum’s swing only depends on two things: the length of the string and the strength of the gravitational field.
Here’s the equation:
T=2*pi*sqrt(l/g)
T is the period of the swing (measured in seconds)
Pi is 3.14…
l is the length of the string (measured in meters)
g is the gravitational field strength (also known as the acceleration due to gravity, measured in m/s^2)
If I just algebraically rearrange that equation and solve it for g, I get this:
g = l*(2pi/T)^2
So, once you’ve measured the period, just take pi, multiply it by 2, divide it by the period, and then square it. If your string length was 1, that gives you the gravitational field strength!
If you get something close to 9.8, you know you’re probably on Earth.
Slightly more complex way:
Using the equation I gave above, and this table of the gravitational field strengths of various planets, calculate what length of string would give a period of 1 second. (Or 2 seconds, whatever time you like.) Then make some pendulums of that length.
Set the pendulums swinging, watch their swings, and try to imagine that on another planet they would only take 1 second to swing back and forth.
Maybe it’s just me, but as a kid, I would have found it incredible to have a set of pendulums that would tell me what planet I was on.
Artificial Gravity!
I’ve been watching The Expanse, and I love seeing their depictions of different methods of making artificial gravity in space. Here are two that would be very fun to talk about with students:
Spin gravity.
You can make people feel like they’re on a planet by making a giant cylinder and spinning it.
Basically, what gravity does is speed us up, (accelerating us towards the center of our planet). So, if we can mimic that “speeding up” feeling, we can mimic gravity.
Whenever we travel in a circle, we have to keep “speeding up” towards the center. (We have to keep turning. If left to our own devices, we’d move in a straight line. To move in a circle, we have to turn. That turning is an acceleration, which is what we feel. You can feel this when you take a tight turn in a car.)
This acceleration towards the center is called centripetal acceleration. Here’s the equation for it:
a=v^2/r
a is the acceleration
v is the speed you’re going
r is the radius of the turn
For this activity, have students design a spaceship that would mimic the Earth’s gravity (or that of whatever fictional planet they want to invent 🙂)
How big would they want the cylinder to be? It can be any length, but they’ll need to decide on a radius, and also how fast the thing will need to spin.
Often times, it’s useful to talk about the time it takes for the thing to spin around once (the period of revolution) instead of the speed. Here’s the equation that relates those two:
v=2*pi*r/T
v is the linear speed
r is the radius of the cylinder
T is the period
(This equation looks complicated, but it’s just speed = distance/time. The distance is the circumference of the circle, which is 2pi*r)
“Grav boots”
On The Expanse, characters use boots that have electromagnets in them that hold them to whatever surface they’re walking on (as long as it’s metal, of course.)
I get why they did this in the show. You can’t just have people floating around. But, the thing is, everything else around them would be weightless. Every tool they used would float. Their hair would float. Their arms would float out from their sides.
Walking in grav boots would be completely different than walking on a planet. I’m sure we could adapt and figure it out, but when we’re walking on a planet, every single atom of us is pulling towards the ground. Our whole body is adapted so that the weight of our torso pushes down, and our bones hold us up.
Imagine holding up your foot and having someone yank on your foot. That’s what a grav boot would feel like.
What was normally a push in our bodies would become a pull.
Anyway, the biomechanics of this are just so interesting. It seems like a reasonable thing to have in the show, but it would be incredibly hard to adapt to.
As I mentioned earlier, gravity gets weaker as you get farther away. Specifically, it obeys something called an “inverse square law” which means if you get twice as far a way it gets a fourth as strong. If you get three times as far away, the force is one ninth what it was, etc.
This can be tough for students to get a concrete sense of, so I made this little story activity to explain it.
It also includes some bonus 3-D geometry stuff.
https://www.mathwithsarah.com/stories/inversesquarelaw
Gravity Fairy Tale Audiobook!
The audiobook narrator, Dave Melcher, just finished the Gravity Fairy Tale audiobook, and it’s up and available now!
Outer Wilds Video Game
I always have to mention this game when I talk about gravity. It’s truly incredible. You pilot a cute little spaceship around a tiny solar system, but the thing is the way they did the gravity and the orbits is all totally accurate.
Getting the hang of the spaceflight is really hard, but it’s a pretty amazing educational experience.
It also really makes Newton’s First Law hit home. Because if you keep firing your rockets you speed up and speed up and speed up and then you end up careening into your destination or shooting past it at ridiculous speeds.