Two simple observations:

One: We can observe that a burst of gas/air that is “puffed” at a target surface will exert a force (push) against said surface.

Two: If the distance between the source that is “puffing” gas and the target surface is increased, the resulting effective force against said surface decreases.


How can we visualize such an effect? There are various experiments that can be done to observe the described effect, what follows is a description of a test bed setup that is simple and inexpensive to set up.


As illustrated in fig 1, all that is necessary is a test bed (1), an apparatus/nozzle (2)that will “puff” air in a given direction, a target surface (3) made of light material not attached to the test bed, a bellows foot pump (4) all enclosed in a transparent box(5)


The dimensions of the box were 3m long, 40cm height and width.



Fig 1


We place the target (3) a short distance (D1) from the nozzle (2), when we give the foot pump (4) a strong squeeze we shall observe that target (3) reacts to the force of air by moving a short distance (R1)


Fig 2


If we repeat the experiment (fig 2) after increment the distance (Dx) between nozzle (2) and target (3) we shall observe the resulting movement (Rx) decreases, we can state that the resulting effective force on a surface by a burst of air is reduced when the distance that separates the nozzle and target is incremented.


Fig 3



This described observation is possible when the dimensions of the box are sufficient to encourage a turbulent behavior of the “puffed” air, if we encloses the “puffed” air in a duct (tube), the air will behave in laminar flow fashion and the resulting distance the target moves does not vary in the same magnitude as when a turbulent behavior is allowed (Figs 3 and 4).


Fig 4


Expelling bound molecules (solid) from the nozzle to the target


Fig 5


If a ball is attached to the nozzle, and we repeat the experiment we shall observe:


Fig 6



When the bellows foot pump is pressed, the burst of air propels the ball until it collides with the target, a measurable  movement (Rb1) is observed.



Fig 7


If we increment the distance separation the nozzle from the target (Dx) we will see that the resulting durance (Rbx) does not differ in the same magnitude as in figs 1 to 3, therefore deduce that the force received by the target (when a solid hurled at it) is not dependent on the distance (within a reasonable margins) behaving as expected in normal classroom experiments that demonstrate the conservation of linear momentum. 

Next page ( will show a superior method of demonstration using balancing masses, a metrology similar to Henry Cavendish’s 1706 experiment to measure the force of gravity between masses

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