SHM - Energy & SHM *was missed*

Question 1

How does a freely oscillating object oscillate with a constant amplitude?

Answer 1

• no friction acting on it
• only forces acting combine to provide the restoring force

Question 2

What happens when friction is present?

Answer 2

• amplitude of oscillations would gradually decrease
• oscillations would eventually cease

Question 3

Assuming there is no friction present, decribe how the nergy of an oscillating object changes? in a spring system

Answer 3

• energy of system is constant
  
  • equal to max E_p
• E_p
  
  • changes with displacement x from eqm,
    
    • in accordance with equation Ep = 1/2 kx²
• total energy
  
  • E_T = 1/2 kA²
  • equal to max Ep
• E_k
  
  • EK = ET - EP = 1/2 k (A² - X²)

Question 4

Describe the features of an energy-displacement graph?

Answer 4

• Ep is paraboolic
• Ek is an inverted parabolla

Question 5

What are dissipative forces? WHy are they called this?

Answer 5

• forces causing the amplitude to decrease
• because they dissipate the energy of the system to the surrounding as thermal energy
• motion is said to be damped

Question 6

What are the types of damping?

Answer 6

• Light damping
  
  • occurs when T is independant of A, so each cycle takes same length of time as the oscilations die away
  • amplitude gradually decreases by the same fraction each cycle
• critical damping
  
  • just enough to stop system oscillating after it has been displaced from eqm
  • returns to eqm in shortest possible time without overshooting when critical
  • car suspension to make comfortable ride
• heavy damping
  
  • damping so strong that the displaced object returns toeqm much more slowly that if the system is critcally damped, no oscillating motion occurs