4.4 Simple Harmonic Motion Flashcards
Define simple harmonic motion
A particle moves with simple harmonic motion if:
1. its acceleration is proportional to its displacement from a fixed pt
2. the direction of the acceleration is always towards that fixed pt
Describe energy during SHM of a simple pendulum
as the bob moves down from its highest position, gpe is converted to ke
As it moves upwards again, ke is converted back into gpe
total energy remains constant with time
Describe energy during SHM of a loaded spring
ke that exists when it is moving is converted to potential (strain) energy as it is compressed
this is converted back to ke again when stretched
total energy remains constant w time
what are damping forces
resistive forces acting on an oscillating system
describe undamped oscillations
- free vibrations
- constant amplitude with time
describe lightly damped oscillations
amplitude of oscillations will gradually get smaller until they eventually cease
describe over damped oscillations
- does not oscillate from its equilibrium position
- system returns very slowly to its equilibrium position
describe critical damping
when damping forces are such so that the system can return to its equilibrium position in the shortest possible time
shortest poss time for any oscillating system to return to its equilibrium position is T/4
Why are electrical meters, such as ammeters, critically damped
so that the pointer movs to the reading as quick as possible without any oscillations
what is a forced vibration
occurs when any external force which varies with time is used to make an object oscillate
What is resonance
takes place when the frequency of the driving force is the same as the frequency of the oscillating system
How does resonance work in guitars
the vibrations of air inside the body of the guitar produce the louder sound that we hear
the vibrations of the string cause the air inside the guitar to vibrate at the same frequency
this is resonance
How does resonance work in tuning forks
when a tuning fork is struck and held over an air column of appropriately long length, a much louder sound is heard
this is because the tuning fork causes the air in the column to vibrate at its natural frequency
this is resonance
Hows does resonance work in electrical circuits (television and radio receivers)
the natural freq of the electrical circuit is altered to match the incoming electromagnetic wave, such as radio transmission
the magnetic component of that wave acts as the driving force
causing the electrons in the circuit to vibrate w a larger amplitude
How does resonance work in a microwave oven
the oven generates microwaves os specific frequency which correspond to the frequency of rotation of water molecules inside the food
the electric component of the electromagnetic wave is used
the microwaves force the water molecules to rotate faster as they move around colliding w other water molecules
this heats up the water and hence the other pats of the food that its in contact with
