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