10035    STE g by Freefall Apparatus

(c) 2006 STE UK Ltd

Principles of operation

A switch in the upper unit releases a steel sphere, held in place by an electromagnet. The action of releasing the steel sphere also initiates the external timer by changing the output from open circuit to closed circuit. When the sphere strikes the target plate a microswitch is activated and thus the timer is stopped.

A "normally open" or "normally closed" output can be selected, depending on the timer being used. The robust instrument is simple to use and gives repeatable and reliable results.

A suitable timing device is STE 10019 Precision Laboratory Timer which has automatic range selection in centiseconds and milliseconds. This timer is strongly recommended as a practical, easily configured unit. It has very simple wiring connections suitable for use with the STE g by Freefall Apparatus, and comes with a 12Vdc, 350mA power supply to energise the solenoid.

N.B. Some alternative g by Freefall devices are offered with low precision timers or stopwatch. These may not have the required resolution.

Components

• Upper unit with toggle switch, solenoid and support rod
• Lower target unit with micro switch
• Steel sphere

Additional equipment required

• An electronic timing device with 100th second increment, e.g. STE 10019,
• Six leads with 4mm plugs
• Retort stand with bosshead clamp

Wiring configuration with STE 10019 Timer

Unit is powered using the black and red mains leads.

Left connection on upper unit = upper start on lab timer

Right connection on upper unit = lower start on lab timer

NC left connection on base unit = upper stop on lab timer

NC right connection on base unit = lower stop on lab timer

See also STE 10019 Precision Laboratory Timer instructions

 Instructions for use

• Clamp the upper unit to the retort stand by means of the support rod and adjust to the required height. The sphere retention fitting must face downwards. Ensure that the switch is in the off "down" position prior to connecting the power source. Place assembly on a flat, stable surface.
• Place the target unit below the upper unit so that the sphere contact is directly above the centre of the target plate. For longer falls the retort stand can be placed at the edge of a table top and the target switch on the floor.
• Connect the power supply to the upper unit via the red/black terminals. Activate the electromagnet by switching to the on "up" position. Hang the steel sphere from the retention fitting on the underside of the upper unit, it should be held in place by the electromagnet.
• Test the alignment of the two units, switch the toggle switch to the down position to release the sphere. The sphere should strike the target plate near the centre, if not adjust and try again.
• When in position the apparatus is ready to be connected to the timing device. If using the STE 10019 laboratory timer, the upper unit is connected to the start gate and the normally open output of the lower unit should be connected to the stop gate at the rear of the timer. The "nc" output is for timers which require a normally closed input in order to trigger.
• Apply the following procedure if using a STE 10019 as the timing device:

1) Press the reset button to zero the time display.

2) Activate the toggle switch to the "up" position and suspend the sphere from the retainer.

3) Switch to the "down" position, this action will release the sphere and simultaneously start the timer. The timer should stop the moment the sphere strikes the target plate.

4)Repeat the experiment with varying lengths of drop.

 Equation of freefall

For the experiments conducted with this apparatus, where a body is falling from an initial rest. The following simple motion equation can be used.                            

                             s = 0.5 x a x t

where s = distance, a = acceleration, t = time