The length of the pendulum will affect the time it takes to complete an oscillation.
Conclusion The periodic time for a simple pendulum can be used to calculate g at any point. The following formula can be used to calculate this:
g = 4o 2 ( l ___ T2 NOTE
The formula is derived from Chapter 9 on SHM periodic time, where 4π2 the slope of this graph gives you a value for g.
Errors
The following errors should be considered when studying this experiment:
• determining the exact position of where the cycle starts/stops
• friction between the string and the cork )
g = acceleration due to gravity (m s–2), l = length of pendulum (m), T = periodic time for one oscillation (s)
• air resistance • angle of swing being too large • retort stand moving • parallax error in measuring the string length.
Precautions
• Confer with your lab partners as to where the cycle points occur.
• Use a thin, strong string for suspending the bob. • Keep draughts to a minimum. • Keep the angle of the swing below 5˚. • Secure the retort stand with weights. • Find the average of your length readings and verify them with your lab partners.
Possible exam questions 1.
2. 3. 4.
5.
Does the decrease in amplitude affect the period? Why do you take a large number of oscillations? Why must the angle of swing be less than 5˚?
Why should the length of the pendulum be at least 40 cm?
How could increasing the length of the string reduce the number of oscillations required?
