Experiment 1: Using the Spine Simulator

Apparatus: The “Spine Simulator”

          To simulate a backpack loading a back’s spine, a custom “Spine Simulator” experimental apparatus is designed and constructed.  Figure 5 shows the complete set-up.   The different parts to the Spine Simulator are listed and shown below:

The Spine

          A plastic tube (51” long and 1 1/2” in diameter) from an old hockey net is used to represent the spine.  It is stiff enough yet can bend under force … like our back’s spine.  The top portion of the tube is cut with grooves so that it can bend more like the spine.  The lower portion, simulating the legs is made rigid by inserting a wooden dowel inside the lower portion of the tube.

         The “spine/leg” unit is then attached securely to a stable metal base to keep the unit vertical.    The complete unit also “stands” on a home use weight scale.  

Figure 5: Spine Simulator Apparatus

The Backpack and Distributed Load   

        A metal grid, sized 12” by 16” and strapped securely to the spine portion of the tube, simulates the experimental “backpack”.  The grid allows for precise hanging of various weights to simulate varying the distribution of loads within the “backpack”.  Figure 6 shows a close-up of the grid “backpack” with colour coded positional labels and a weight, representing the distributed load positioned at MBC for this example.

Without a load in the backpack, this neutral state of the back is monitored by a positional indicator identified in Figure 6 as N. Under load, the spine and backpack bends to a position identified as L.

Figure 7 defines the colour coded positional labels.

Figure 6: Close-Up of Experimental Grid "Backpack

Counterbalance Force Mechanism

          When the backpack is loaded causing the “spine” to bend from its neutral position, a counterbalancing force is applied to the “spine” to pull it back to its initial neutral position.  The mechanism to do this task consists of a wire tied to the top of the spine (eg. the “shoulder”) and connected to a Newton Spring Scale (figure 8).

          A plastic tube inserted into a metal base extender attached to the metal base helps to guide the wired Newton Spring Scale to measure the horizontal Counterbalancing Force.

          The effort made by the experimenter to stabilize the load back to its neutral position represents what a person would do instinctively when carrying a loaded backpack (figure 9)

          To monitor the effect of adding loads to the “backpack”, the bottom of the tube “spine/leg” unit sits on a scale (figure 10)

Figure 8: Newton Spring Scale

Figure 9: Applying the Counterbalancing Force to a Loaded "Backpack"

Figure 10: The "Spine/Leg" Unit Standing on a Scale

Materials

1.   Various weights with hooks were needed.  Four 1 kilogram weights were used.  The researcher thanks Ms. Passarelli, Gr. 8 teacher at Canadian Martyrs School, for providing the researcher with these items. 

2.   A Newton Spring Scale was used to measure the force that was needed to bring the apparatus back to neutral.  The researcher again thanks Ms. Passarelli for providing the researcher with this instrument.

Figure 11: A 1 kg Weight and a Newton Spring Scale

3.     A scale to read the vertical force.

4.     A digital camera to record the results.  I thank my father for generously supplying his services to provide the pictures.

Experiment 1: Procedure

          Using the Spine Simulator Apparatus, loads of 1 kg, 2 kg, 3kg and 4 kg are  hooked onto the grid “backpack” at the twelve various locations (TL, TC, TR), (MTL, MTC, MTR), (MBL, MBC, MBR) and (BL, BC, BL).  The locations were approximately equally spaced but not exactly.  In retrospect, this could have been.  In all, there are 48 different combinations of positions and loads.

In each case, the loads will cause the “spine” to bend from its neutral unloaded position requiring applying a Counterbalancing Force, F to bring the “spine” back to its neutral position as monitored by the N indicator.

Figure 12: Applying a Counterbalancing Force to stabilize the loaded Backpack

          The Counterbalancing Force for each of the 48 combinations is measured using the connected Newton Spring Scale.  The measurements are recorded and presented in the figures 13 to 25.

Go To Experiment 1 Data