Physics Photo of the Week
November
7, 2008
Thrust Reaction - Discussion by Lauren Parker
According to
Dictionary.com, Thrust is a “linear reactive force exerted by a
propeller, propulsive gases, etc., to propel a ship, aircraft, etc.”
Warren Wilson student Alex Chambers decided to outfit himself in a
helmet and ride a rolling cart to demonstrate this principle. In this
case, thrust comes from the propulsion of carbon dioxide from the fire
extinguisher, causing Alex’s cart to accelerate in the opposite
direction of the gas.
Thrust is a vector quantity that relates to Newton’s 
Second and Third Laws.
The Third Law states that “every action has an equal and opposite
reaction.” The fire extinguisher ejects the gas toward the left.
The reaction of pushing the gas to the left results in the gas pushing
Alex and the cart to the right. Newton's Second Law states that
acceleration is inversely proportional to mass and directly
proportional to force, a = f/m. The mass of the expelled gas is defined
as the mass per unit time, or the mass flow rate. The amount of gas
that is accelerated and the difference in velocity of the gas in the
extinguisher versus the gas exiting the nozzle determine the magnitude
of the thrust and thus Alex’s acceleration.
Physics
Photo of the
Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to dcollins@warren-wilson.edu.
All photos and discussions are copyright by Donald
Collins or by the person credited for the photo and/or
discussion. These photos and discussions may be used for private
individual use or educational use. Any commercial use without
written permission of the photoprovider is forbidden.
Click
here to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
