00:15Hello, 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. Before we dive into
00:52centripetal force, it's important to look at Newton's first law of motion, which states that
00:57an object will continue moving with a constant velocity along a straight path unless acted upon
01:03by a net external force. This means that the Space Station will move along a straight path if it
01:08weren't for one key external force acting on it, Earth's gravitational pull. Another name for this
01:15external force is centripetal force. A centripetal force is any net force that keeps an object moving
01:21along a circular path. Gravity, in this case, is a centripetal force because it is the force that
01:27is keeping our Space Station moving in its circular path around Earth.
01:35Okay, now you know that gravity constantly pulled the moving object with linear momentum inward,
01:41just 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.
02:00This is considered low Earth orbit. It is high enough to encounter very little interference from
02:06the atmosphere but low enough to be relatively easy to travel to. Let me show you some examples of angular
02:12momentum being conserved in the microgravity environment aboard the station. I will apply a
02:17force to set this yoyo in motion. The force of tension is transferred through the string,
02:22which 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 and the string? As I'm holding the string between two fingers on one hand
02:49to keep the axis of the rotation stable, I'm going to pull the string with my other hand, increasing the
02:54tension and centripetal force and decreasing the radius of the yoyo's orbit. As the radius of the yoyo's
03:00orbit decrease, its velocity increased. Angular momentum is the product of an object's velocity,
03:06mass, and the radius of its orbit from an object's center. If you only have centripetal force, angular
03:13momentum must also be conserved. So if the radius of its orbit decreases, its velocity must increase in
03:19order to maintain its angular momentum. Let's try this again, but this time I'll decrease the tension
03:26on the string, lowering 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.
03:47As 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.
04:27Thank you for exploring some physics with me today, and see you soon!
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