Gravity & The Solar System

It’s just after the long weekend here in Canada, where I spent most of my weekend playing Skyrim, and wasting time, but relaxing all at the same time. You don’t care about that though, all you care about is what you clicked on right? So let’s jump right into it! (also: still slightly hungover, no pictures in this one..)

We all know (re. should know..) that gravity is a force which pulls us towards a mass, in the case of the Earth it’s at a rate of 9.8 meters a second. When comparing that with other forces in the universe, it’s actually relatively weak. It’s so easy to overpower gravity that a thrust of about 11km/s is all you need to leave the Earth’s surface, and venture off to say hi to the ISS and Curiosity. Assume that your car can travel 90 degrees from the surface of the Earth (straight up), it would only take about 1 hour to get to the atmosphere.

Here’s what you don’t know. Astronauts are weightless, right? They float around and have to use special vacuum toilets to do their business, right? Wrong. Astronauts are still falling at a rate of 9.8m/s, just like someone who parachutes out of a plane or jumps off a diving board into the pool, they all fall at 9.8m/s. They appear to be floating because they’re orbiting the Earth at a speed which is equally pulling them away from Earth at the same rate, called centripetal force. You can see this effect yourself with a bucket and some water. Fill it about an inch and then use your arm and spin it as fast as you can, the water will remain in the bucket until the force you’re applying to it, becomes weaker than the pull of gravity. Traveling at roughly 7.7m/s, if they were to slow down even 1m/s, those Astronauts would go kerplunk and fall to the “floor”, the floor being whatever side is facing the Earth.

The ISS vs. Earth is one example, what about something bigger, say the Earth and the Sun? If you were to say jump up and down once, would the pull of gravity the Sun has on the Earth not pull it just a tiny bit more, starting our spiral of eventual doom? No, and we partially know why this can’t happen because of an earlier blog posting here. Just like the ISS vs. Earth, the Earth spins at 29.8km/s around the Sun. The pull of gravity the Sun has on the Earth is 29.8km/s, it’s perfectly balanced!

Even if that one person jumping moved Earth just a bit closer to the sun, giving it just a tiny bit more of a pull of gravity, it still wouldn’t happen, because Earth isn’t perfectly circling the Sun. It’s elliptical (oval) orbit around the sun allows it to speed up and slow down slightly, correcting for jerks jumping up and down on it’s surface. What would happen if that person jumped and moved Earth closer to the sun, the Earth would speed up and overshoot it’s elliptical orbit, causing it to now become slightly farther away from the Sun, balancing out the one jump. Even if all the people on Earth jumped at the same time it wouldn’t move the Earth more than a few inches closer. A few inches on a scale of the average distance of Earth to the Sun being just under 149.6 million kilometers, isn’t anything to matter.. It would be like you moving your desk a few atoms to the left so you can be closer to the heater. You wouldn’t even feel a difference.

OK.. one picture..

Jeff Wilton

Jeff is the founder and owner of Everyday Science Stuff. ESS is a one man operation, with the core belief that all education should be served without crippling debt tuition, without revenue generating ads and without any restrictions of any kind such as paywalls, forced login and account creations, geographical restrictions, and so on.

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