Acceleration due to gravity

    By measuring the time of free fall of a body we can calculate 'g' from the equation S = g * t * t / 2 , where S is the distance and t is the time of flight. Time is done in the following manner.
        An electromagnet is powered to hold a small iron ball. Software then releases the ball and marks the time of start. The ball drops on a flat sufface where a loudspeaker is kept face down. The speaker output is amplified and given to the LSB of digital input.
When the ball hits the surface the vibrations make the digital input high momentarily. This time interval between releasing the ball and it hitting the plate below is measured by the program using PCs internal timer clock. The values obtained are given below.

Time

Distance

Accn. due to gravity

0.36457

65

978

0.35058

60

976

0.33622

55

973

0.32036

50

974

0.30296

45

981

The same experiment can be done using different types of sensors. Optical sensors made of LEDs and phototransistors can sense the falling object at a particular position.