Gravity is one of the four fundamental forces and on Earth, it pulls everything towards the center of the Earth. According to Newton’s second law, since gravity is a force, it will cause any mass to accelerate. The objective of this experiment is to find the acceleration of any mass due to gravity on Earth. Since the Earth has an atmosphere, free fall of a mass is technically not possible due to the constant upward drag caused by wind. However, when the mass itself is many times denser than air, the effect of air resistance on its movement can be neglected.
Hence, to find the acceleration due to gravity (g) in this experiment; all the students were given metal bob pendulum. Since a metal bob’s density is many times higher than air and its spherical shape is aerodynamic, the effect of air resistance on its downward descent could be ignored. where S = distance travelled, u = initial speed, t = time and a = acceleration. For this experiment, the above equation modifies to. This is because the distance travelled is equal to the height from which the metal bob is dropped, initial velocity (u) is 0 and acceleration is equal to the acceleration due to gravity (g).
VARIABLES: Independent Variables: 1. The height from which the ball was dropped. Dependent Variables: 1. The time taken for the ball to drop Controlled Variables: 1. Metal Bob – The same metal bob was used for all trials at all heights. 2. Reaction time – One member of the group was responsible for timing all the trials so that delays due to his reaction time negate each other. 3. The measuring tape – The same measuring tape was used to measure all heights. PROCEDURE: The metal bob was dropped from heights of 9. 0cm, 17. 0cm, 25. 0cm, 33. 0cm and 41. 0cm.
The time taken for the bob to cover the distance was measured using a microphone attached to a CRO that produced a voltage spike as soon as the ball dropped producing a sound that was picked up by the microphone. Safety Precautions: 1. Covered shoes were worn so that accidentally dropping the bob would not hurt our feet. 2. Since the bobs bounced high, it was ensured that any fragile item in the vicinity was taken care of. As it can be seen from the total uncertainty calculation, the experimentally deduced value for the acceleration due to gravity on Earth is accurate to a large extent.
In fact, the literature value of 9. 81m/s2 is extremely close to highest end of the range of experimental data—9. 69m/s2 to 9. 79m/s2. The difference between 9. 81m/s2 and 9. 79m/s2 is understandable but excusable. The r2 value for the line of best fit is 0. 9999 which shows excellent correlation between the value of H and t2. This confirms the fact that acceleration does not change and always remains a constant 9. 81m/s2 on the surface of Earth. The error bars exist on the graph but they are not so prominent because the absolute errors are very insignificant.
However, for the fourth value, the uncertainty is comparatively larger and hence, the distance between the three gradient lines are considerably legible. The uncertainty, however small cannot be ignored and it must be explored so that if possible, it can be avoided in the future. Firstly, the recording of the height was not done with a very precise ruler. A lot of time and effort was spent to ensure its accuracy in the readings and not let its faults hinder the experimental results.
This is could be avoided if a more precise ruler or instrument to measure height could be present. Secondly, although the voltage spike generator (CRO) was undeniably accurate, no information about any time delays in the microphone was known. The possibility of microphone causing a significant lag, in spite of the ball falling close to it is very improbable but nonetheless, it exists. The effects of air resistance were ignored because of their very ignorable influence on the readings.
The mild influence on the readings in this experiment might partially be owed to the effect of air resistance. Perhaps, a more aerodynamic object could be used but investing in those are not worth unless the major sources of systematic error such as the imprecise ruler and the doubtful microphone are replaced with reliable, accurate and precise instrument. Ultimately, this experiment serves to remind us of the experimental nature of Physics and in the course of this experiment, many doubts were cleared with regard to instruments and techniques.