This section contains descriptions of how to use our Millisecond Timer (IPC-3834-T) and Digital Millisecond Stopclock (IPC-3750-T or TKL-557-W) with the 'g' By Freefall apparatus supplied by Griffin. This document deals with both the Griffin apparatus (Griffin catalogue number XBR-601-H) and the STE apparatus (XBR-620-W) and gives detailed descriptions and diagrams of how to set up the experiments and how to connect in each case to either the Millisecond Timer or the Digital Millisecond Stopclock.

Permission is granted for these pages to be downloaded and copied as necessary. We welcome any comments or suggestions on any matter relating to these experiments.

1. Clamp the solenoid unit and the gate switch onto a retort stand with the solenoid positioned above the gate switch so that a metal sphere held by the solenoid, when released, will fall through the gate switch and cause it to open. It may be necessary to position a solid item under the switch to limit its amount of motion after the metal sphere has operated it. Otherwise the gate may swing freely and return to its original (closed) position.

2. Connect the gate switch terminals to the Millisecond Timer sockets marked 'B'. Also connect a 0.1µF capacitor across the 'B' sockets. This will help to stop spurious timer operations caused by 'noisy' operation of the gate switch.

3. Connect the solenoid unit terminals in series with the normally closed contacts of one pole of the double pole, double throw switch and to the power supply (use the d.c. terminals of a Dual Output Power Supply set to 2-5V or equivalent). See fig. 1.

4. Connect the normally open contacts of the other pole of the double pole, double throw switch to the Millisecond Timer sockets marked 'A'. As before, connect a 0.1µF capacitor across the 'A' sockets.

5. Switch on the power supply and position a metal sphere on the solenoid. Ensure the gate switch is closed and reset the Millisecond Timer to read 0.000.

6. Operate the double pole, double throw switch to release the sphere and to start the timer.

7. If the apparatus was correctly set up and operated, the gate switch will open and will stop the timer. In our experiments this experimental set up yielded very repeatable results.

1. Clamp the solenoid unit and the gate switch onto a retort stand with the solenoid positioned above the gate switch so that a metal sphere held by the solenoid, when released, will fall through the gate switch and cause it to open. It may be necessary to position a solid item under the switch to limit its amount of motion after the metal sphere has operated it. Otherwise the gate may swing freely and return to its original (closed) position.

2. Connect the solenoid terminals in series with the contacts of one pole of the double pole, double throw momentary switch and to the power supply (use the d.c. terminals of a Dual Output Power Supply set to 2-5V or equivalent). See fig. 2.

3. Connect the gate switch terminals in series with the contacts of the second pole of the double pole, double throw momentary switch and to the Digital Millisecond Stopclock sockets. Connect a 0.1µF capacitor across the stopclock terminals to help stop spurious stopclock operations due to 'noisy' switch contacts.

4. Switch on the power supply and position a metal sphere on the solenoid. Ensure the gate switch is closed and reset the Digital Millisecond Stopclock to read 0.000.

5. Operate and release the double pole, double throw momentary switch to release the sphere and to start the timer. N.B. it is essential that the switch is operated and released back to its original position before the metal sphere operates the gate switch. This is not as difficult as it sounds! This is necessary as there is only one set of terminals on the Millisecond Stopclock so the series circuit connected to them needs to be broken then remade before being broken again. This starts then stops the timer. In our experiments we were able to get reliable results with solenoid-gate switch distances as small as 10cm.

6. If the apparatus was correctly set up and operated, the gate switch will open and will stop the timer. In our experiments this experimental set up yielded very repeatable results.

1. Clamp the solenoid unit onto a retort stand and position the switch platform so that a metal sphere held by the solenoid will fall onto the centre of the platform and cause it to operate when released. In our experiments we found it necessary to incline the switch platform sideways at an angle of approximately 30°. If the platform is used in a flat position the metal sphere will bounce upon hitting it and will cause the switch to operate a number of times giving spurious timer readings. With the switch platform inclined, the metal sphere will hit the platform cleanly and will be deflected away, operating the switch only once. See fig. 3.

2. Connect the solenoid unit yellow terminals to the Millisecond Timer sockets marked 'A'. Connect a 0.1µF capacitor across the sockets to help stop spurious timer switching due to 'noisy' switch contacts.

3. Connect the solenoid black and red terminals to the power supply (use the d.c. terminals of a Dual Output Power Supply set to 12V or equivalent). See fig. 4.

4. Connect the normally closed contacts of the switch platform (marked 'NC') to the Millisecond Timer sockets marked 'B'. As before, connect a 0.1µF capacitor across the sockets.

5. With the solenoid unit switch in the up position attach a metal sphere to the solenoid. Operate the solenoid unit switch to release the metal sphere and start the timer.

6. If the apparatus was correctly set up and operated, when the metal sphere hits the switch platform the switch will operate once and stop the timer.

1. Clamp the solenoid unit onto a retort stand and position the switch platform so that a metal sphere held by the solenoid will fall onto the centre of the platform and cause it to operate. In our experiments we found it necessary to incline the switch platform sideways at an angle of approximately 30°. If the platform is used in a flat position the metal sphere will bounce upon hitting it and will cause the switch to operate a number of times giving spurious timer readings. With the switch platform inclined the metal sphere will hit the platform cleanly and be deflected away operating the switch only once. See fig. 3.

2. Connect the solenoid unit yellow terminals in series with the switch platform normally closed contacts to the Digital Millisecond Stopclock sockets marked 'EXTERNAL START/STOP'. Connect a 0.1µF capacitor across the sockets to help stop spurious timer switching due to 'noisy' switch contacts.

3. Connect the solenoid black and red terminals to the power supply (use the d.c. terminals of a Dual Output Power Supply set to 12V or equivalent). See fig. 5.

4. With the solenoid unit switch in the up position attach a metal sphere to the solenoid. Operate the solenoid unit switch to release the metal sphere and start the timer.

5. If the apparatus was correctly set up and operated, when the metal sphere hits the switch platform the switch will operate once and stop the timer.

Both the Millisecond Timer and the Digital Millisecond Stopclock are based on crystal controlled microprocessors and as such an accuracy of ±0.1% for each instrument can be expected.

In each case the distance from the solenoid to the switch should be measured accurately and noted. When the time of fall has been determined for a given distance, the acceleration due to gravity can be calculated from the equation of motion:

s = ½gt²

where:

s = distance (in metres)

g = acceleration due to gravity in metres/second²

t = time of fall (in metres)

The value of g obtainable from these experiments is 9.81m/s².