Hover Disc--Centripetal Force

This Week's Big Questions:
1. What does it mean to analyze forces in 3D?
2. How do forces cause objects to move in a circle?
3. What does it mean to be in orbit? How do satellites orbit planets? How do planets orbit the sun?

 What does it mean to say that we live in a 3D universe? By using the term 3D, we are saying that there are 3 dimensions of space (x, y, and z). Examples of this on earth include the latitude, longitude and altitude of a particular spot on Earth. Actually, it may be better to say that we live in a 4D world. This includes time ( t ). The important thing to remember is that when we analyze these dimensions, we can analyze them separately or independent of one another using SIN and COS (or SOH CAH). Using these, we can analyze a piece of wire by making it a triangle (portrait problem). This week, we explored the use of forces involved in causing objects to move in a circle using a hover disk, which eliminated friction force (unlocked the ridges between the disk and the floor). We moved this disk in a circle using constant speed. When we drew the free body diagram of the disk as it was spinning, there were 3 forces acting on the disk (gravitational, normal, and tension) the normal and gravitational forces cancelled each other out because they were balanced--meaning that because the disk was travelling at constant speed (Newton's 1st law) the normal force was the same as the gravitational force. This left tension. This central pointing net force (centripetal) is what made the disk move in a circle. Without this net force, the disk proceeded in a straight line at constant speed. Since the disk felt a net force towards the center, it moved towards the center . But because it was moving fast enough, the disk began moving around the center. You can be at constant speed in a circle while accelerating. The only thing that changes is direction. Remember, acceleration does not necessarily mean speeding up. When an object is moving in a circle, it is accelerating because its direction of motion is changing and whenever the acceleration is perpendicular to the velocity, the object changes direction but is still at constant speed.

This relates to Earth and how we orbit around the sun. We are moving at constant speed (about 60,000 mph) around the sun with nothing to stop us. In this case, the centripetal force is the sun. Earth has a gravitational rope pulling us around the sun. This is what disproves the idea that there is no gravity in space. If there was no gravity (or no rope) the earth would move away from the sun in a straight line at constant speed. We got the initial speed that propelled us around the sun (just like the force that we applied to the disk in order to get it moving)  from the creation of our solar system. Even though the gravitational force is weaker, it still exists in space. In regards to the moon, the  center is Earth and the center pointing net force  (centripetal force) is gravity which it to fall around the earth. This is how orbits happen.