Physics Photo of the Week
Thrust Reaction - Discussion by Lauren Parker
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.
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