Free and forced vibration

Question 1

What is resonant frequency?

Answer 1

• if you stretch and release a mass on a spring, it oscillates at its resonant frequency
• freq at max amplitude

Question 2

What happens if no energy is transferred to or from surroudnig

Answer 2

it will keep oscillating with the same amplitude forever

Question 3

When do forced vibrations happen?

Answer 3

• when there is an external driving force
• system can be forced to vibrate by a periodic external force
• the frequency of this is called the driving freuqency

Question 4

When are the driving frequency in phase with the resonant frequency?

Answer 4

• when driving frequency is less than the resonant frequency
  
  • the oscillator just follow the motion of the driver
• if the driving freq is greater than the resonannt freq, the oscillator will not be able to keep up and will be oscillate

Question 5

When does resonance happen?

Answer 5

• driving freq = resibabt freq
• 90 degress phase difference between oscillator and driver

Question 6

What happens as the driving freq approaches resonant freq

Answer 6

• system gains more and more energy from the driving force
• and so vibrates with rapidly increase amplitude
• when this happens the system in resonating

Question 7

When does damping happen?

Answer 7

• when energy is lost to the surroudning
• in practice, any oscillating system loses energy to its surroundings

Question 8

WHat causes damping?

Answer 8

• damping forces
• e.g. friction like air resistance

Question 9

What is the effect of damping, and what does heavier damping mean?>

Answer 9

• damping reducess the amplitude of the oscillation over time
• the heavier the damping, the quick the amplitude is reduced to zero

Question 10

What is critical damping?

Answer 10

• reduces the amplitude in the shortest possible time

Question 11

How does damping affect resonance

Answer 11

• lightly
  
  • sharp resonance peak
  • their amplitude only increases dramatically when the driving freq is very close to resonant freq
• heavily damped system
  
  • flatter response
  • ampltude doesn’t increase much near the resonant freq and they aren’t as sensitive to the driving freq
• lighter the damping
  
  • larger max ampltide at resonance
  • closer the resonant freq is to natural freq of system

Question 12

What are the types of damping?

Answer 12