Physics Demo Number: 015

Approximate Run Time: 5 min

Fire Extinguisher Rocket Cart

Demo Description

Use a fire extinguisher to propel a cart forward.

 

Scientific Principles

  • Newton's Third Law

  • Conservation of momentum

Equipment

  • 3 wheel cart

  • Modified fire extinguisher

 

Equipment Location

  • The cart lives on the floor in SC4228 along the back left wall next to Chemistry prep room.

  • Fire extinguishers for rocket motor are in [H-5-1] , about opposite the cart.





Instructions

The photos show the three-wheeled cart used to show rocket principles. The motor (RM) is a 10-lb CO2 fire extinguisher, which has had all the diverting mechanisms cut off so that when the hand valve is squeezed all the escaping CO2 goes in one direction, producing a thrust way in excess of 20 or 30 lbs.

It is VERY DANGEROUS to open the valve without proper support for the extinguisher !!
It is STRONGLY SUGGESTED that one place (RM) inside the tank-bracket (TB) and secure it firmly with the tightening bolt (TT) !!

Note that near the top right of the V in VU in the left lower photo one can see (TT).

When the tank is properly secured the exhaust-tube (ET) should be aligned parallel to the cart’s symmetry-axis.

(SSB) is the seat safety-bolt which must be inserted from the bottom of the plate it is hanging through ( see also the lower left photo) and tightened into the threaded hole (TH) in the metal plate attached to the bottom of the seat.

In the event one is foolishly determined to make a screaming-turning exit from the lecture room into the hall or prep room, it is difficult enough to keep the cart from rolling over to the side without having to worry about the seat flipping around.

Since there is a brake shoe on only one rear wheel a fully screaming exit cannot be brought to a straight-line halt. One must turn sharply while braking.

The safest procedure is to let off the throttle by the end of the lecture table and brake to a stop in a straight line. In this event, one need not worry about (SSB) or roll overs.

One must give a week or two notice of intention to demonstrate the rocket cart to ensure having a newly fueled tank.

One should never start the rocket motor from the prep room side of SC4327 or SC 4309; the blast will break major things in the prep room, unless the doors are firmly latched closed.

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Writeup created by David A. Burba
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