00:00Hello, my name is Sultan al-Niyadi and I'm an astronaut living and working on board the
00:20International Space Station. Any idea how it's possible for the Space Station to continuously
00:25orbit Earth 250 miles above the surface? And why at 17,500 miles per hour? What would happen if the
00:33station speed up or slowed down? We are going to explore those questions and more by investigating
00:39the connection between the angular momentum and the orbits in our microgravity environment.
00:45But first, you need to know a couple of other terms. Let's get started.
00:50Before we dive into centripetal force, it's important to look at Newton's first law of motion,
00:56which states that an object will continue moving with a constant velocity
01:00along a straight path unless acted upon by a net external force. This means that the space
01:06station will move along a straight path if it weren't for one key external force acting on it,
01:11Earth's gravitational pull. Another name for this external force is centripetal force.
01:18A centripetal force is any net force that keeps an object moving along a circular path. Gravity in
01:24this case is a centripetal force because it is the force that is keeping our space station moving in
01:29its circular path around Earth. Okay, now you know that gravity constantly pulls the moving object with
01:40linear momentum inward just enough to cause it to travel in a curved path, making its momentum angular.
01:48The International Space Station maintains this balance between gravity and linear momentum
01:53by traveling at the required 17,500 miles per hour to maintain an altitude of 250 miles.
02:01This is considered low Earth orbit. It is high enough to encounter very little interference from the
02:06atmosphere but low enough to be relatively easy to travel to. Let me show you some examples of angular
02:11momentum being conserved in the microgravity environment aboard the station.
02:15I will apply a force to set this yoyo in motion. The force of tension is transferred through the
02:21string which is a centripetal force keeping this yoyo revolving around my hand. But what happens when I
02:27let go of the string? Once the tension from the string is removed, the object continues to follow
02:32Newton's first law of motion. It keeps moving at a constant velocity along a straight path relative to the
02:38space station. Now what happens to the motion of the yoyo if we increase the centripetal force
02:43by increasing the tension in the string? As I'm holding the string between two fingers on one hand to keep
02:49the axis of the rotation stable, I'm going to pull the string with my other hand, increasing the tension
02:55and centripetal force and decreasing the radius of the yoyo's orbit. As the radius of the yoyo's orbit
03:01decrease, its velocity increased. Angular momentum is the product of an object's velocity, mass, and the
03:08radius of its orbit from an object's center. If you only have centripetal force, angular momentum must
03:14also be conserved. So if the radius of its orbit decreases, its velocity must increase in order to
03:20maintain its angular momentum. Let's try this again, but this time I'll decrease the tension on the string,
03:28lowering the centripetal force and increasing the radius of the yoyo's orbit.
03:34If you thought the velocity of the yoyo would decrease, you were right. Since angular momentum
03:39must be conserved, if the radius of an orbit is increased, the velocity of the yoyo must decrease.
03:48As you can see, there is an inverse relationship between the radius of the orbit and the yoyo's
03:52velocity. I was able to change the velocity of the yoyo by increasing and decreasing the centripetal
03:58force in the system. We can't do this with the orbit of the station or other satellites because
04:03we can't change the pull of gravity exerted by Earth. Instead, to keep the station in a stable
04:09circular orbit, we use thrusters that can help maintain the constant speed of 17,500 miles per hour.
04:17To learn more about these topics, check out the corresponding classroom connection to conduct
04:22your own experiment and discover other ways angular momentum plays a part in your daily life.
04:26Thank you for exploring some physics with me today, and see you soon!
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