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 and the string? As I'm holding the string between two fingers on one hand to
02:49keep 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 orbit
03:01decrease, its velocity increased. Angular momentum is the product of an object's velocity, mass, and the radius
03:08of its orbit from an object's center. If you only have centripetal force, angular momentum must also
03:14be conserved. So if the radius of its orbit decreases, its velocity must increase in order to maintain its
03:20angular momentum. Let's try this again, but this time I'll decrease the tension on the string, lowering the
03:28centripetal force and increasing the radius of the yoyo's orbit. If you thought the velocity
03:35of the yoyo would decrease, you were right. Since angular momentum must be conserved, if the radius of
03:41an orbit is increased, the velocity of the yoyo must decrease. As you can see, there is an inverse
03:49relationship between the radius of the orbit and the yoyo's velocity. I was able to change the velocity
03:55of the yoyo by increasing and decreasing the centripetal force in the system. We can't do this
04:00with the orbit of the station or other satellites because we can't change the pull of gravity exerted
04:05by Earth. Instead, to keep the station in a stable circular orbit, we use thrusters that can help maintain
04:12the constant speed of 17,500 miles per hour. To learn more about these topics, check out the corresponding
04:20classroom connection to conduct your own experiment and discover other ways angular momentum plays a
04:25part in your daily life. Thank you for exploring some physics with me today and see you soon.
Comments