How is it possible for the ISS to stay in orbit? Learn more about the science behind orbiting Earth and more in this NASA "STEMonstrations" video.
Credit: NASA Johnson Space Center
Credit: NASA Johnson Space Center
Category
🤖
TechTranscript
00:00 [ Music ]
00:16 >> Hello, my name is Sultan Al-Niyadi
00:17 and I'm an astronaut living and working
00:19 on board the International Space Station.
00:22 Any idea how it's possible for the space station
00:24 to continuously orbit Earth 250 miles above the surface?
00:28 And why at 17,500 miles per hour?
00:32 What would happen if the station sped up or slowed down?
00:36 We are going to explore those questions and more
00:38 by investigating the connection between the angular momentum
00:42 and the orbits in our microgravity environment.
00:45 But first, you need to know a couple of other terms.
00:49 Let's get started.
00:51 Before we dive into centripetal force, it's important to look
00:54 at Newton's first law of motion,
00:56 which states that an object will continue moving
00:59 with a constant velocity along a straight path unless acted upon
01:03 by a net external force.
01:05 This means that the space station will move along a
01:07 straight path if it weren't
01:09 for one key external force acting on it,
01:11 Earth's gravitational pull.
01:14 Another name for this external force is centripetal force.
01:18 A centripetal force is any net force
01:20 that keeps an object moving along a circular path.
01:23 Gravity, in this case, is a centripetal force
01:26 because it is the force that is keeping our space station moving
01:29 in its circular path around Earth.
01:32 [ Music ]
01:36 Okay, now you know that gravity constantly pulls a moving
01:39 object with linear momentum inward just enough to cause it
01:42 to travel in a curved path, making its momentum angular.
01:46 The International Space Station maintains this balance
01:51 between gravity and linear momentum by traveling
01:54 at the required 17,500 miles per hour
01:57 to maintain an altitude of 250 miles.
02:01 This is considered low Earth orbit.
02:03 It is high enough to encounter very little interference
02:05 from the atmosphere, but low enough
02:07 to be relatively easy to travel to.
02:10 Let me show you some examples
02:11 of angular momentum being conserved
02:13 in the microgravity environment aboard the station.
02:16 I will apply a force to set this yo-yo in motion.
02:19 The force of tension is transferred through the string,
02:22 which is a centripetal force keeping this yo-yo revolving
02:25 around my hand.
02:26 But what happens when I let go of the string?
02:28 Once the tension from the string is removed, the object continues
02:31 to follow Newton's first law of motion.
02:34 It keeps moving at a constant velocity along a straight path
02:37 relative to the space station.
02:39 Now, what happens to the motion of the yo-yo
02:41 if we increase the centripetal force
02:43 by increasing the tension in the string?
02:45 As I'm holding the string between two fingers on one hand
02:49 to keep the axis of the rotation stable,
02:51 I'm going to pull the string with my other hand,
02:54 increasing the tension and centripetal force
02:56 and decreasing the radius of the yo-yo's orbit.
02:59 As the radius of the yo-yo's orbit decreases,
03:01 its velocity increases.
03:03 Angular momentum is a product of an object's velocity, mass,
03:07 and the radius of its orbit from an object's center.
03:11 If you only have centripetal force,
03:13 angular momentum must also be conserved.
03:15 So if the radius of its orbit decreases,
03:18 its velocity must increase in order
03:20 to maintain its angular momentum.
03:23 Let's try this again, but this time,
03:25 I'll decrease the tension on the string,
03:28 lowering the centripetal force and increasing
03:30 the radius of the yo-yo's orbit.
03:34 If you thought the velocity of the yo-yo would decrease,
03:37 you were right.
03:38 Since angular momentum must be conserved,
03:40 if the radius of an orbit is increased,
03:43 the velocity of the yo-yo must decrease.
03:48 As you can see, there is an inverse relationship
03:50 between the radius of the orbit and the yo-yo's velocity.
03:53 I was able to change the velocity of the yo-yo
03:56 by increasing and decreasing the centripetal force
03:58 in the system.
03:59 We can't do this with the orbit of the station
04:02 or other satellites, because we can't change the pull
04:04 of gravity exerted by Earth.
04:06 Instead, to keep the station in a stable, circular orbit,
04:10 we used thrusters that can help maintain the constant speed
04:13 of 17,500 miles per hour.
04:18 To learn more about these topics,
04:19 check out the corresponding classroom connection
04:21 to conduct your own experiment and discover
04:23 other ways angular momentum plays a part in your daily life.
04:27 Thank you for exploring some physics with me today,
04:29 and see you soon.
04:31 [MUSIC PLAYING]
04:35 (dramatic music)