Demos: 2C-12 Magnus Force on a Rotating Cylinder


This demonstration is similar to 2C - 7. A circular cylinder is attached to the center of a Pasco low-friction cart which rides on a smooth track. Air flow directed from a fan blows across the cylinder at right angles to the track. If the cylinder is spinning, the Magnus force is in a direction perpendicular to the air flow, which in this case is along the track. The cart will move down the track under the action of the force. If the cylinder is spun in the opposite sense, the cart will move in the opposite direction.

Directions: First direct the air stream across a non-spinning cylinder. Be careful to direct the flow at right angles so that there is no component of the air stream directed along the track. Attach the cord through the hole in the axis at the top of the cylinder and wind up the string. Give the string a firm pull to set the cylinder spinning. Then direct the stream again at right angles to the track. Stop the spinning and wind the string in the opposite sense. Repeat the demo.

Suggestions for Presentation: If you have done the demo 2C - 7, remind the students of the origin of the Magnus force (a Bernoulli phenomenon). Tell them the direction of the spin on the cylinder and ask them to predict which direction the cart will move. What happens if you change the spin direction?

Applications: At one time, a ship was proposed (and built) that made use of the Magnus force for propulsion. Two spinning cylinders stood on the deck of the ship. As the wind blew transverse to the direction of the ship’s motion, the Magnus force gave an additional push to the ship. Evidently this technique was not cost-effective.

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Last Updated: May 9, 2016 11:44 AM