P201 Lab 4: Newton's Second Law
Equipment List
Format: Item Name (Location)
  1. Photogate Timer (46B)
  2. DC power supply (45D)
  3. Air track (34A, 35A, 36A, 37A)
  4. Red Air Track Glider (40D and 40E)
  5. 2 Pulleys (43B)
  6. Weight Set (45C)
  7. Weight Hangers ~50g (45D)
  8. Black String (35C - Box labeled Newton's 2nd)
Lab Setup and Diagnostic Help Section
These are the items that should be present at every lab station.
The clamps in this picture are needed as well, I just couldn't fit them into the first picture.

The screwdriver is needed as well, for the TA's use during this lab.
I've found the best way to attach the string is to unscrew the screw on the top, wrap the string around the screw, and retighten the screw.  This will keep the string in place without the need for a knot that typically results in the cutting of the string to get it loose again.

You'll want to make sure the flag is PARALLEL to the direction of motion, if it isn't, you will get funny (if any) results during the photo-gate timing section of this lab.
You'll then want to set the air track diagonally across the table.

Then, at each end you'll want to use the pulleys provided.  Some of the air tracks have a pulley at one end, so you can use that pulley or the table-attached type.  I'd personally go with the table types, the ones on the air track tend to have a good deal of friction about the bearings.

Another thing to make sure of is to make sure the string is fairly straight with the direction of the track.  If you look carefully here, you'll see the string isn't aligned very well.
You can fix the string's alignment by (1) adjusting the pulley or (2) moving the air track.  I've found moving the air track is faster and easier.

Another thing to make sure is that the pulley itself isn't twisted.  This can be adjusted by loosening the small wing nut on the bottom and then simply turning the pulley wheel.
The wing nut you'll want to loosen is shown here.  This loosens the whole pulley assembly from the mount assembly so you can twist the pulley or move it up and down.
Sometimes you'll get a pulley setup like this.  I'm not sure why they come back after every lab set like this, it makes no sense.  What's key to notice here is that the axis of the adjustment bolt and the wing nut is PARALLEL with the direction of motion, you don't want this, you want the axis to be perpendicular.
Close up for clarity's sake.

This can be fixed by simply undoing the wing nut all the way, and moving the whole assembly to the perpendicular hole.
Now, put a weight hanger on the string and loop the string over the pulley.
Here is how you want to set up the photogate.

Make sure the photogate's IR diode is above the string line but below the top of the flag.
Based on P201 Lab manual last revised on 12/4/00  ISBN: 1565819748

©2004 Mark Hanni, IUPUI Department of Physics