1 00:00:10,043 --> 00:00:15,882 The Gables. 2 00:00:15,982 --> 00:00:18,618 Hello, my name is Sultan Alneyadi and I’m an astronaut 3 00:00:18,618 --> 00:00:21,955 living and working aboard the International Space Station. 4 00:00:22,022 --> 00:00:24,691 Any idea how it's possible for the space station 5 00:00:24,691 --> 00:00:28,628 to continuously orbit Earth 250 miles above the surface? 6 00:00:28,695 --> 00:00:32,565 And why at 17,500 miles per hour? 7 00:00:32,665 --> 00:00:36,403 What would happen if the station sped up or slowed down? 8 00:00:36,503 --> 00:00:39,739 We are going to explore those questions and more by investigating 9 00:00:39,739 --> 00:00:42,042 the connection between the angular momentum 10 00:00:42,042 --> 00:00:45,045 and the orbits in our microgravity environment. 11 00:00:45,278 --> 00:00:48,982 But first, you need to know a couple of other terms. 12 00:00:49,082 --> 00:00:51,684 Let's get started. 13 00:00:51,684 --> 00:00:53,820 Before we dive into a centripetal force, 14 00:00:53,820 --> 00:00:57,223 it's important to look at Newton's first law of motion, which states 15 00:00:57,223 --> 00:01:00,460 that an object will continue moving with a constant velocity 16 00:01:00,527 --> 00:01:05,231 along a straight path unless acted upon by a net external force. 17 00:01:05,298 --> 00:01:08,301 This means that the space station will move along a straight path 18 00:01:08,334 --> 00:01:14,140 if it weren't for one key external force acting on it, Earth's gravitational pull. 19 00:01:14,240 --> 00:01:19,412 Another name for this external force is centripetal force. A centripetal force 20 00:01:19,412 --> 00:01:23,216 is any net force that keeps an object moving along a circular path. 21 00:01:23,283 --> 00:01:26,252 Gravity in this case is a centripetal force 22 00:01:26,252 --> 00:01:27,320 because it is the force 23 00:01:27,320 --> 00:01:35,929 that is keeping our space station moving in its circular path around Earth. 24 00:01:36,029 --> 00:01:36,830 Okay. 25 00:01:36,830 --> 00:01:40,467 Now you know that gravity constantly pulls the moving object with linear 26 00:01:40,467 --> 00:01:44,337 momentum inward just enough to cause it to travel in a curved path, 27 00:01:44,404 --> 00:01:48,741 making its momentum angular. 28 00:01:48,842 --> 00:01:52,212 The International Space Station maintains this balance between gravity 29 00:01:52,212 --> 00:01:57,016 and linear momentum by traveling at the required 17,500 miles 30 00:01:57,016 --> 00:02:00,987 per hour to maintain an altitude of 250 miles. 31 00:02:01,054 --> 00:02:03,323 This is considered low earth orbit. 32 00:02:03,323 --> 00:02:05,892 It is high enough to encounter very little interference 33 00:02:05,892 --> 00:02:09,896 from the atmosphere, but low enough to be relatively easy to travel to. 34 00:02:09,963 --> 00:02:13,233 Let me show you some examples of angular momentum being conserved 35 00:02:13,233 --> 00:02:16,569 in the microgravity environment aboard the station. 36 00:02:16,636 --> 00:02:19,472 I will apply a force to set this yoyo in motion. 37 00:02:19,472 --> 00:02:22,408 The force of tension is transferred through the string, 38 00:02:22,408 --> 00:02:25,945 which is a centripetal force keeping this yoyo revolving around my hand. 39 00:02:26,146 --> 00:02:26,946 But what happens 40 00:02:26,946 --> 00:02:30,650 when I let go of the string once the tension from the string is removed? 41 00:02:30,750 --> 00:02:34,053 The object continues to follow Newton's first law of motion. 42 00:02:34,120 --> 00:02:37,657 It keeps moving at a constant velocity along a straight path 43 00:02:37,657 --> 00:02:39,726 relative to the space station. 44 00:02:39,726 --> 00:02:42,328 Now what happens to the motion of the yoyo if we increase 45 00:02:42,328 --> 00:02:45,598 the centripetal force by increasing the tension in the string? 46 00:02:45,832 --> 00:02:49,135 As I'm holding the string between two fingers on one hand 47 00:02:49,202 --> 00:02:52,772 to keep the axis of the rotation stable, I'm going to pull the string 48 00:02:52,772 --> 00:02:56,342 with my other hand, increasing the tension and centripetal force 49 00:02:56,576 --> 00:02:59,379 and decreasing the radius of the orbit. 50 00:02:59,379 --> 00:03:03,583 As the radius of the orbit decreased, its velocity increased. 51 00:03:03,683 --> 00:03:06,886 Angular momentum is a product of an object's velocity, 52 00:03:06,986 --> 00:03:11,024 mass and the radius of its orbit from an object's center. 53 00:03:11,124 --> 00:03:15,562 If you only have centripetal force, angular momentum must also be conserved. 54 00:03:15,662 --> 00:03:18,765 So if the radius of its orbit decreases, its velocity 55 00:03:18,765 --> 00:03:23,369 must increase in order to maintain its angular momentum. 56 00:03:23,436 --> 00:03:25,939 Let's try this again, but this time 57 00:03:25,939 --> 00:03:29,576 decrease the tensiojn on the string, lowering the centripetal force 58 00:03:29,709 --> 00:03:34,147 and increasing the radius of the orbit. 59 00:03:34,214 --> 00:03:38,051 If you thought the velocity of the yo yo would decrease, you were right. 60 00:03:38,284 --> 00:03:43,156 Since angular momentum must be conserved if the radius of an orbit is increased, 61 00:03:43,256 --> 00:03:47,860 the velocity of the yo yo must decrease. 62 00:03:47,961 --> 00:03:50,196 As you can see, there is an inverse relationship 63 00:03:50,196 --> 00:03:53,633 between the radius of the orbit and the velocity. 64 00:03:53,733 --> 00:03:55,335 I was able to change the velocity 65 00:03:55,335 --> 00:03:59,405 of the yo-yo by increasing and decreasing the centripetal force in the system. 66 00:03:59,472 --> 00:04:02,875 We can’t do this with the orbit of the station or other satellites 67 00:04:02,875 --> 00:04:07,146 because we can change the pull of gravity exerted by earth. 68 00:04:07,213 --> 00:04:10,083 Instead, to keep the station in a stable circular orbit, 69 00:04:10,083 --> 00:04:11,084 we use thrusters 70 00:04:11,084 --> 00:04:17,757 that can help maintain the constant speed of 17,500 miles per hour. 71 00:04:17,824 --> 00:04:20,927 To learn more about these topics, check out the corresponding classroom 72 00:04:20,927 --> 00:04:24,330 connection to conduct your own experiment and discover other ways 73 00:04:24,330 --> 00:04:27,300 angular momentum plays a part in your daily life. 74 00:04:27,300 --> 00:04:29,969 Thank you for exploring some physics with me today. 75 00:04:29,969 --> 00:04:36,809 See you soon.