PAG 10.2 Observing Forced and Damped Oscillations

Question 1

What are free oscillations?

Answer 1

Natural oscillations of a system, without any driving or energy addition.
They occur at the natural frequency of the system

Question 2

What is damping?

Answer 2

Removal of energy from a system, resulting in the amplitude of oscillation reducing

Question 3

What is resonance?

Answer 3

Occurs when the oscillations of a system are at the natural frequency.
The amplitude of the oscillations, and the rate of energy transfer are at a maximum

Question 4

What are forced oscillations?

Answer 4

Oscillations caused by a periodic driving force.
The frequency of oscillations depends on that of the driver

Question 5

How can the resonant frequency of a system be determined from a graph of amplitude against frequency?

Answer 5

The resonant frequency will be the frequency at which the amplitude is maximum, sharp peak

Question 6

How can the amplitude of a mass-spring system be measured?

Answer 6

A position sensor can be used to record the system’s amplitude.
The amplitude is the maximum displacement from the equilibrium position

Question 7

How can the time period of a mass-spring oscillator be measured?

Answer 7

A fiducial marker can be placed at the equilibrium position.
The time taken for 10 complete oscillations can be recorded using a stopwatch, divide by 10 to obtain the time period for a single oscillation

Question 8

How can damping be added to a mass-spring oscillation

Answer 8

Piece of card can be added to the oscillator to damp its oscillations by increasing the air resistance that acts on it

Question 9

In what direction does the damping force act?

Answer 9

A damping force acts in a direction such that is opposes the system’s oscillations

Question 10

What piece of apparatus could be used in the lab to produce forced oscillations

Answer 10

Signal generator could be attached to a vibration generator to produce forced oscillations.
The frequency of oscillations can be varied by changing the frequency of the signal inputted

Question 11

What safety precautions should be taken when applying a load to the spring?

Answer 11

Always wear safety goggles in case the spring snaps.
The applied load should not exceed the maximum capacity of the spring.
Spring begins to deform plastically, do not add further load

Question 12

How can the frequency of oscillations be calculated from the time period?

Answer 12

Frequency is the inverse of the time period

Question 13

If a system experiences no damping, how will the oscillations very over time?

Answer 13

Without damping, the oscillations of a system would carry on infinitely and the amplitude would remain constant

Question 14

Why does the amplitude of the oscillations in our experiment decreases even without a damping card attached?

Answer 14

The oscillating system will still experience some damping in the form of air resistance and friction.
These forces remove energy from the system over time, and causes the amplitude of oscillations to decrease

Question 15

What safety precautions should be taken when hanging a load from a clamp stand?

Answer 15

A counterweight or G clamp should be attached to the base of the clamp stand to provide a counter moment and prevent the stand from toppling

Question 16

What is the advantage of using a position sensor in this experiment?

Answer 16

A position sensor allows you to measure the displacement of the oscillator with a greater accuracy.
If the sensor and software package can also plot against time, it will also reduce the uncertainty in your time period measurements

Question 17

Describe the difference in the decay of amplitude for a system with and without a damping card attached

Answer 17

Both system will decay over time, but the system with the damping card will experience greater damping and so its amplitude will decrease at a faster rate