Relative Velocity and Vectors - Relative Velocity

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Relative Velocity and Vectors

Relative Velocity

On the morning of June 21, 2004, SpaceShipOne climbed to over 62 miles and landed at the same landing strip it took off from. This amazing feat is in preparation for pursuing the ANSARI X-Prize and reperesentst the first time a privately funded aircraft made it into space! Cool, huh?

This is a $10,000,000 prize to jumpstart the space tourism industry through competition between the most talented entrepreneurs and rocket experts in the world. The $10 Million cash prize will be awarded to the first team that:

Privately finances, builds & launches a spaceship, able to carry three people to 100 kilometers (62.5 miles)
Returns safely to Earth
Repeats the launch with the same ship within 2 weeks

This is a photo of the White Night turbojet flying over SpaceShipOne (SSO). Pretty funky looking if you ask me...

If you wanted to know how fast SSO traveled, you would first have to answer the question, "Compared to what?". You could get data from:

Ground-based stations
White Night
Satellites
- Geosynchronous
- Non-synchronous orbits

This brings up the concept of "Frames of Reference." There is no preferred frame, so there is no "right" answer to the question of how fast the SSO traveled. Whenever there is relative motion, we need to be clear on the frame of reference we choose to use.

Most of us will never make it into space, but we will all end up in an airplane. With airplanes, pilots need to consider the ground speed, the air speed, and the wind speed.

(These images are from the wonderful Multimedia Physics Studio web site.

Assume that the aircraft in each of these three examples produced the same amount of thrust. Therefore, the plane's speed would be constant from the air's frame of reference. However, with a tailwind, the ground speed would be greater, a headwind would result in a slower ground speed, and the cross wind would cause a greater ground speed and a changed direction.
To model a plane's motion accurately, we need to consider the relative velocities aircraft, wind and ground. That means we need to make use of vectors. Check the next lesson... :

Vectors: vector.doc