Free Fall speed, and g the gravitational constant

In this activity you can measure the elapsed time of a falling object at different distances using the proximity sensors.  A simple Scratch program can be created to do the timing.

Steps:

 

Consult the images below

Set the FunKey board into I/O mode

  • unplug all connections to the FunKey board

  • connect an alligator clip from D to K

  • plug in the usb cable to the computer

  • see that the LED next to I/O Mode is lit

  • remove the alligator clip

  • unplug the USB cable from the computer

Install proximity sensors

  • find two proximity sensors and red/black/white cables with the black connectors on the end.  These attack to pins on the sensors and FunKey board connections W and D

  • attach the black connectors on the cables to the pins on the each of the proximity sensors: red to VCC, black to GND and white to OUT

  • attach the other end of the cables to the W and D pin connections on the board.  red to the middle pin labeled "+", black to the top pin labeled "-" and white to the lower pin labeled S

  • plug in the usb cable to the computer

  • see that the tiny green led on the right side of the sensor is lit, which means it is getting power.

  • the tiny green led on the left should NOT be lit

  • bring your hand near the sensor, in front of the clear and dark red plastic parts

  • you should see the left led light up when your hand or a piece of paper is nearby, and go dark when you take it away.

  • if it stays lit all the time, you must adjust the "trimpot", which is the square blue component with a white center on the proximity sensor board.  Turn the white part with a tiny screwdriver, paperclip or similar until the left tiny green led just goes off, but lights when your hand or a piece of paper is nearby.

Doing the timing

  • The proximity sensor connected to the W connection will send an "O" keystroke when it detects something nearby, like a falling ball or piece of cardboard.  The proximity sensor connected to the D connection will send a "U" keystroke when it detects something nearby.

  • Test this by using a simple text editor and you should see the O and U.  You'll also see a "P" on the W sensor and an "I" key on the D sensor when the object moves away from the sensor.  You can ignore these "move away" keystrokes in your program

  • Create a Scratch program that resets the timer when it detects the O key and reads the timer when it detects the I key.

  • Attach the sensors to a meter stick, to the wall or a table leg or similar vertical surface, with the two proximity sensors at a given distance apart, say 10 cm, and with the clear and dark red components pointing outward

  • Drop a ball or piece of cardboard from just above the top sensor, so it passes in front of the clear and dark red plastic detectors, and starts and stops the timer as the object passes the proximity sensors.  This gives the elapsed time for the given distance

  • Make similar measurements at different distances between the two sensors. With the two 20 cm cables you should be able to get up to about 40 cm of distance, so you could make elapsed time measurements of 5, 10, 20, 30 and 40 cm fall distances.

  • Remember to start the falling object just above the top sensor so it does not have a "starting velocity", but starts at 0

  • plot the results on graph paper.

  • using the formula s = 1/2 * g * t* t solve for g and find the gravitational constant

Unplug all cables

Be sure USB is NOT connected

Attach alligator from D to K

set io mode 2.JPG

Connect USB cable to board and computer

set io mode 1.JPG
set io mode 3.JPG

Unplug alligator

Blue LED should light at "I/O Mode"

prox sensors 1.JPG

Attach proximity sensors to cables

prox sensors connected.JPG
prox sensor cable connection.JPG

Attach cables to FunKey board W and D connections

Connect red/black/white to sensor pins as shown

prox cable board D.JPG
prox cable board W.JPG

Attach red/black/white cable to W connection pins on FunKey board

Attach red/black/white cable to D connection pins on FunKey board

Video shows proximity sensor detecting close object, here a piece of paper and lights the left tiny green LED.  This is the correct operation.  If the left LED is on all the time, you need to adjust the threshold.

If the left LED is on all the time, you need to adjust the level with a tiny screw driver. Video shows how to adjust the "trim pot" so the left LED is just at the threshold of light and dark, so that it only lights when an object is near and is NOT on all the time.