SHM Practicals

The AH today were working in 3 groups to research via practicals and notes about SHM. The task is given below. Well done to Morford and Hodgson who created the following from their practical, with very little assistance. Their results were so good I thought I’d share them.

Mr Morford wrote
“These graphs are from our recent experiment to determine the effect of damping on an oscillating mass. A mass was hung from a spring over an Alba Ranger ultrasound device. We then analysed our measurements using excel and graphed our results to find the decay due to damping.”

Morford & Hodgson (2019)
Check out the great phase lag and the obvious proof of SHM showing a is proportional to -ky
The period isn’t constant because the spring started moving with horizontal motion but the amplitude certainly deteriorated
I’ll need to check this….but it looks good!

This was the task for the class and my thanks to the IoP for their Practical Physics lessons and to the other places referenced for some great practical techniques. I will neaten this post later, but I promised Morford and Hodgson that I would post tonight!

Hopefully I can collate the rest of the groups information soon.

By the end of the lesson you should……

  • You to have the spring constant for two of the springs by two different methods.
  • A graph of d against t, v against t, and a against t
  • A value of the period of spring for various masses
  • Discovered the effect of amplitude on the period Found the effect of damping (so find out what that is)

https://www.webassign.net/question_assets/ncsucalcphysmechl3/lab_7_1/manual.html

https://www.birmingham.ac.uk/undergraduate/preparing-for-university/stem/Physics/stem-legacy-SHM.aspx

https://www.cyberphysics.co.uk/topics/shm/springs.htm

http://practicalphysics.org/investigating-mass-spring-oscillator.html

2020

Despite Covid-19 the intrepid AH students have been showing damping with a pendulum bob and tracker. The original movie has still to be analysed by our friends from Annan

This is Courault and Douglas with bob skimming the water and you can see some damping on the graph. Note the period remains constant but the amplitude, and hence energy is reduced. Well done Courault and Douglas, imortalised in your tracker movie!
This is Patterson and Pritchards attempt with bob fully immersed as it goes through its swing. You can see bob is far more damped! I think Pritchard was a little lazy with his identification of the edge of bob as that period is definitely changing! Compare this damping with the previous one. Well done to both of you!

Now if we can add Atwal, Burns, Carson and Morrin’s tracker we can have a full set for 2020 and you can look back with fondness at your time in AH, despite all the distancing.

Investigating a mass-on-spring oscillator

Demonstration

A mass suspended on a spring will oscillate after being displaced. The period of oscillation is affected by the amount of mass and the stiffness of the spring. This experiment allows the period, displacement, velocity and acceleration to be investigated by datalogging the output from a motion sensor. It is an example of simple harmonic motion.


Analysis 
Measurement of period 
Period and Amplitude Observe that the period appears to be independent of amplitude. 
 
Effect of mass 
A straight line is the usual result, showing that the period squared is proportional to the mass. 
 
Velocity and acceleration 
A plot of the resulting data shows a ‘velocity vs. time’ graph. Note that the new graph is also sinusoidal. However, compared with the ‘distance vs. time’ graph, there is a phase difference – the velocity is a maximum when the displacement is zero, and vice versa. 
 
A similar gradient calculation based on the ‘velocity vs. time’ graph yields an ‘acceleration vs. time’ graph. Comparing this with the original ‘distance vs. time’ graph shows a phase difference of 180°. This indicates that the acceleration is always opposite in direction to the displacement. Teaching notes

Aim: To find the force constant of a helical spring by plotting a graph between load and extension.

Aim: To find the effect of damping on an oscillating spring

Aim: To find the effect of mass on an oscillating spring

Aim: To use the formula for an oscillating spring to find m or k etc

Signature
December 2020

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