Chapter 3 Part 3 Addition of Velocities

Prof. Clements Notes/Hints for Physics Courses

Chapter 3 Open Stax College Physics or Most Introductory Physics Courses

Addition of Velocities

I highly recommend that you go to the web site https://openstax.org/details/books/college-physics to access the free OpenStax College Physics textbook and resources.

YouTube videos of my (usually short) lectures and example problems are indexed at http://www.physics.gpclements.com/ . There are also a few videos that give review of basic math tools that are used in an introductory physics course.

Terms you should know at the end of this unit: vector addition

Addition of Velocities

In these situations there is usually motion of an object in a medium that is also moving. The motion of the object is a vector. The motion of the medium is a vector. To analyze the problem you will add the two vectors.

Imagine a small airplane flying at 120 miles/hour at an angle of 30 degrees North of East. At least those are the numbers the pilot programmed into the computer that controls the flight of the plane. After one hour of flying the pilot discovers that the plane is 140 miles from the starting point at an angle of 35 degrees North of East. What could cause the airplane to end up at this position after one hour?

One answer would be that there was a “tailwind” pushing the plane with the tailwind having a little sideways component (relative to the direction of the plane) that changed the angle for the displacement. That is, the wind direction was more than 30 degrees North of East.

You can solve problems that involve motion in a moving medium (airplane in windy air; boat in a river, etc.) by adding vectors. You need to add the vector of the motion to the vector for the motion of the medium. The resultant is the actual motion of the object.

If you are going to study for your private pilot’s license or your captain of a vessel license you should work example problems in this section.

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