Claudio Oliveira Egalon [Egalon - Mechanics: Experiments in Physics

Introduction

This experiment is closely related to Newtons First Law of motion. Accordingly, if the net force in an object is zero, this object will be either at rest or moving with constant velocity. In order to confirm this law, we will use a leveled air track to remove the frictional force between the track and a cart.

Equipment

Air track, spark timer, heat sensitive tape, adhesive tape, air cart (glider), one paper clip, air compressor (one for two groups), hose, rubber bands, string, matches, ruler and meter stick.

Experimental Procedure

1. Clean the surface of the air track and the bottom of the glider. Carefully set the glider on the track and do not slide it across the track while the compressor is off . If you do, you will scratch and damage the track surface.
2. Connect one end of the hose to the connector at the end of the track and the other end of the hose to the connector of the air pump.
3. Turn on the air compressor and level the air track as well as you can. While you adjust the level, the cart should be placed at the very middle of the track. Do not put the cart elsewhere or you will not be able to level the track properly. The cart should either remain at rest or move very slowly.
4. After the track is leveled, turn off the air compressor.
5. Set the spark timer to 60 Hz and log this value, f = 60 Hz, in Table 1-1. 60 Hz means that you are generating 60 sparks per seconds. Do not turn on the spark timer yet and be careful with it!!! This is a high voltage device that, at best, can scare you and, at worst, can electrocute and really hurt you!

Table 1-1. Data and results.

1. With the spark timer off , connect its high voltage terminal (the red cable) to the long wire stretched above the track and along its length. The ground terminal (the black cable) should be connected to the frame of the track. Both cables should be connected to the back of the spark timer. The long wire above the track is electrically insulated from the track frame.
2. Fix the thermal paper along the length of the track, just below the glider, with its white surface facing up.
3. Stretch the paper clip and attach one of its ends to the body the cart. Bend the paper clip so a short section of it is positioned as close as possible to the track wire without touching it . If the clip touches the wire, friction will be added to the motion of the cart. Ensure that the clip does not touch the wire at any position along the track!!! The other end of the clip should be positioned as close as possible to the thermal paper (again it should not touch it).
4. Now that you have the track leveled and the glider, the tape and paper clip mounted on the track, turn the spark timer switch on. At this point, you should move away from the track: do not touch the track surface or the glider otherwise you may be electrocuted !
5. The spark timer has a second switch which, when depressed, activates the sparks. The spark rate is adjusted by a knob on the spark timer: set its rate at 60 Hertz.
6. With the air compressor still off, depress the second spark timer switch and observe the sparks moving from the upper wire all the way down to the lower clip and the thermal tape. If everything is working correctly, a dark spot will form on the thermal tape surface.
7. After you observe the dark spot on the surface of the thermal taper, turn the spark timer off.
8. Attach a rubber band to one of the ends of the track so it can be used as a launcher for the cart.