Demos: 1B-01 Vector Addition of Velocities

Simulating a boat crossing a river, a small toy bulldozer and a large cart are used show how velocities add. It also illustrates motion viewed from different frames of reference.

Directions: Place the cart on the lecture desk and provide enough space to move it approximately its full length. A vertical bar is clamped to the desktop to provide a reference marker. First, hold the cart stationary and have the bulldozer move directly across the cart toward the marker post. This simulates a boat crossing a stream with no stream velocity. Next, with the bulldozer AIMED toward the marker post, set it in motion and move the cart slowly in one direction. This represents a boat crossing a moving stream while pointed directly across the stream. The bulldozer will land “downstream.” Next, if the bulldozer is AIMED upstream, the cart can be moved at just the right speed to make the bulldozer reach the opposite side at the marker.

Suggestions for Presentation: Ask students if they have ever had the experience of crossing a river in a boat. Discuss possible strategies. Or relate it to airplanes flying in a crosswind.

Applications: Vectoring of airplanes in a crosswind and similar situations.

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