Apparatus
Electronic free fall app. (Solenoid, Gate switch, Stand, Electronic timer, Metallic bob, leads) and meter rod.
Diagram
Point to Ponder
Galileo was the pioneer worker to show that all bodies irrespective of their masses or nature falling freely in vacuum had the same acceleration at a given place.
Everyone has observed the effect of gravity as it causes object to fall downward. In the absence of air resistance, it is found that all bodies at the same location above the earth fall vertically with the same acceleration furthermore, if the distance of the fall is small as compared to the radius of the earth, the acceleration remains essentially constant. This idealized motion in which air resistance is neglected and the acceleration is nearly constant is known as free-fall.
The acceleration of a freely falling body is called the acceleration due to gravity denoted by g. The acceleration due to gravity is directed downward towards the Centre of earth. Near the earth surface g is approximately.
g = 9.80 m/s2
Or g = 32.2 ft/s2
An experiment to find the value of g by electronic timer is based on principle to measure accurately the time it takes for a ball to fall through a known height. The acceleration g of the ball is then calculated using one of the equations of motion.
If the ball only falls a meter or so, it doesn’t gain enough speed for air resistance to affect its acceleration. The electronic timer is automatically switched on when power to electromagnet is cut. At the instant the ball starts to fall the timer is switched off when the ball strikes the gate switches. When ball falls, its initial velocity at highest point is zero. Let in time t, it fall from height ‘h’.
vi = 0
a = g
S =h
Time = t
Using second equation of motion
S = vit + 1/2 at2
h = 0 t + 1/2 gt2
h = 0 + 1/2 gt2
h = 1/2 gt2
or g = 2h/ t2
From above equation, the value of g can be calculated.
Procedure
First the electromagnet is made on by pressing magnetism switch and bob is attached at lower end of electromagnet. The electronic timer is reset to get zero reading. Press the start switch, electronic timer starts simultaneously when electromagnet is made off so that bob is detached from it and falls freely.
The timer stops at the moment when bob fall on gate switch. The reading on the timer is noted in centisecond ’t’ (Dividing it by 100 to get time t in seconds). The distance S between gate switch and bob is measured by meter rod. Take six reading by changing the distance S.
Value of ‘g’ can be calculated by using
Observations and calculations:
Precautions:
(1) The distance between the bob and gate switch should be measured correctly.
(2) Distance should be measured from the lower side of bob.
(3) The electronic timer should be reset at 00 before starting the experiment.
