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158-M5 Manual Addendum: Newton’s Second Law V: Procedure Before you attempt any measurements make sure that air is provided to the track at an adequate pressure. Examine the air supply arrangement. Air comes through the pipe and passes through a shutoff valve, then a regulator and then into the air track. The regulator has a threaded “T” handle protruding from the top-this how pressure should be regulated. Do not attempt to regulate pressure using the shutoff valve because as the air system pressure fluctuates (as it certainly will with 9 airtracks running concurrently), there may not be sufficient flow to maintain the pressure set by the regulator. Slowly open the shutoff valve and watch the pressure. With the shutoff valve fully opened, the pressure gauge should read between 14 and 18 psi. Generally, shutoff valves close when turned clockwise (or to the right when looking at the top of the handwheel) and open when turned to the left. This is the same arrangement as most standard threaded fasteners, giving rise to the surprisingly useful mneumonic “Righty-Tighty, Lefty-Loosey” All of the cutoff valves in the labs are of this variety. There is somewhat less standardization in pressure regulators, but more often than not they work in the opposite fashion-clockwise (“Righty”) turning of the adjustment handle will open them and raise the output pressure while counter- clockwise (“Lefty”)will close them off and reduce the output pressure. Once the air pressure is set in the stated range, it will be further adjusted to minimize friction. Another preliminary task is to record the masses of all flags, the glider and the mass holder to the nearest 0.1 g. Selection of air pressure for the air track USE PRE-SELECTED PRESSURE. IF THERE IS A PROBLEM, DO THE FOLLOWING TOGETHER WITH YOUR TA. Step 1: Setup the airtrack as described in section V3, with 10 g on the mass hanger and 40 g on the glider, distributed as evenly as possible. Step 2: Select a start position for the glider and an air pressure (say 16 psi) Step 3: Measure the time Δ t it takes the flag to pass through the photogate Step 4: Increase the air pressure by 2psi and measure the new time Δ t' Step 5: If Δ t' < Δ t then go to step 4 If Δ t' = Δ t then stop. Do not exceed 22 psi into the air track. Leveling the air track Now the air track must be leveled. Place the track in the desired position on the lab table. Once the track is leveled it must not be moved.

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