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MED 101- PHYSICS I > 8. SIMPLE HARMONIC MOTION (SHM) (PART 1) > Flashcards

8. SIMPLE HARMONIC MOTION (SHM) (PART 1) Flashcards

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1
Q
  1. What do we call any motion that repeats after a given period of time?

PROVIDE AN EXAMPLE.

A
  • oscillatory motion

EG: the inner ear
: it works by transmitting sound-wave energy into a
series of vibrating bones

EG : waves

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2
Q
  1. What is a massless spring characterised by?
A
  • it is characterised by the fact that the further you stretch it
  • the harder it pulls back
  • the more you compress a spring
  • the harder it pushes back
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3
Q
  1. What can be said about the magnitude of the force exerted by the spring on an object?
A
  • it is proportional to the stretch of the spring
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4
Q
  1. What does the “stretch” of the spring refer to?
A
  • it refers to how far you have pulled the spring from its natural position
  • NATURAL POSITION= EQUILIBRIUM POSITION
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5
Q
  1. What is the force exerted by a spring on an object called?
A
  • the restoring force
  • it brings the spring back to equilibrium
  • it acts against the applied force
  • it is proportional to the displacement of the spring
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6
Q
  1. Define Hooke’s Law.
A
  • for spring (and any other elastic materials):
    - the magnitude of the restoring force is proportional
    to the displacement of the spring
    from its equilibrium position
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7
Q
  1. How can Hooke’s Law be written in mathematical terms?
A
  • F = -k . x
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8
Q
  1. What do each of the components in the following formula represent:

F= -kx

A
  • F= the magnitude of the force (restoring force)
  • the negative sign (-)= means that the object is moving in
    the opposite direction from the force
    = the restoring force is always
    opposite of the displacement (x)
  • k= the spring constant
    = it measures the spring stiffness
    = it is given in N/m
    = the ratio of the force applied to the resulting change in
    the length
  • x = the distance from the equilibrium position
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9
Q
  1. What happens if you express F as F external in the equation: F= -kx
A
  • this would now give you the external force needed to stretch the spring to a given amount (x)
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10
Q
  1. F external is the negative of the restoring force (F).
    What does this do to the equation?
A
  • it removes the negative
  • F= kx
  • this is because the external force acts in the same direction as the displacement of the object
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11
Q
  1. What does it mean when F external is positive?
A
  • the material/ object is experiencing tension
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12
Q
  1. What does it mean when F external is negative?
A
  • the material/object is experiencing compression
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13
Q
  1. What is simple harmonic motion?
A
  • it is a type of periodic motion
  • the restoring force is proportional to the displacement from the equilibrium position
    ( F ∝ x )
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14
Q
  1. What is periodic motion?
A
  • it is motion that is repeated in equal intervals of time
  • the system doing the motion will then repeat itself
  • it will then return to its initial position after the same amount of time
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15
Q
  1. What stops an Oscillation motion?
A
  • Friction
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16
Q
  1. What is each oscillation in oscillation motion called?
A
  • a cycle
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17
Q
  1. What is the time taken for the system to return to its initial state called?
    This is also known as the time taken to complete one full cycle of oscillation?
A
  • it is called a period
  • the symbol for it is T
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18
Q
  1. What is frequency (f)?
A
  • it has an SI unit called hertz (Hz)
  • it is the number of cycles per second
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19
Q
  1. How is frequency calculated?
A
  • f = 1 / T
  • T is the period of time (in seconds)
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20
Q
  1. How is the period calculated?
A
  • T= 1 / f
  • f is the frequency in Hertz
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21
Q
  1. What does a pendulum consist of?
A
  • it consists of a mass hanging from a light cord
  • this mass swings from side to side
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22
Q
  1. What is the equilibrium point with regards to a pendulum?
A
  • it is the point at which the pendulum is hanging straight down
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23
Q
  1. Which force tends to restore the pendulum to its equilibrium point?
A
  • gravity
24
Q
  1. With regards to working out the restoring force in a pendulum equation, what formula is used?
A
  • F perpendicular ≈ - kx
  • F perpendicular is the gravitational force on the object
25
Q
  1. How would we work out the spring constant of a pendulum?

Why do we work it out this way?

A
  • k = mg / L
  • k = spring constant
  • mg = gravitational force of the object
  • L= length of the cord
  • we work it out this way because there is no spring present
26
Q
  1. How would we work out the period of the pendulum?
A
  • L is the length of the pendulum
  • g= gravitational force
  • π= constant (3.14)
27
Q
  1. What must you first investigate to understand the mechanical properties of different body components?
A
  • you must investigate stress-strain relationships
28
Q
  1. What do we model to understand stress-strain relationships?
A
  • we model nonlinear time-dependent properties
  • we model time-dependent, viscoelastic properties
29
Q
  1. What are these models used for?
A
  • they help to understand how bones can bend
  • they help to understand the occurrence of fractures
30
Q
  1. What are the two mechanical classifications of body parts?
A
  • passive
  • active
31
Q
  1. What are passive components?
    Give two examples.
A
  • they are components which respond to outside forces
  • EG: bones and tendons
32
Q
  1. What are active components?
    Give an example.
A
  • they generate forces
  • muscles
33
Q
  1. Why is this division between active and passive components of the body not ideal?
A
  • because muscles can act as both active elements and passive components
  • it is dependent on the situation
34
Q
  1. What is the simplest type of passive response?
A
  • harmonic
  • Hookean behaviour
35
Q
  1. What are three characteristics of Hookean behaviour?
A
  • the deformations are linear with the applied force and the stresses
  • the response is independent of time
  • all potential energy is stored in media that it can be extracted from
36
Q
  1. What are two examples of elastic media?
    What does elastic media mean?
A

EG: bones
: tendons

Elastic media means that when a force is applied on the object, it will return back to its original position

37
Q
  1. In reality, is any material perfectly harmonic?
A
  • no
38
Q
  1. Why do most materials deviate from perfectly harmonic behaviour?
A
  • they experience large applied forces on them
  • this causes deformations
39
Q
  1. What does the deformation of a material depend on?
A
  • force
  • stress
  • it depends on them nonlinearly
40
Q
  1. Can deformations be reversible?
A
  • yes they can
41
Q
  1. What happens to the elasticity of a material that has experiences a large stress?
A
  • it is no longer elastic
  • it undergoes plastic deformation
  • it is irreversible
42
Q
  1. What does it mean when a material is irreversible?
A
  • it never returns to the same size or shape when the stress is removed
  • it can even fracture if the stresses become larger
43
Q
  1. Define elasticity.
A
  • the property by which a body returns to its original size and shape
  • it does this when the forces that deform it are removed
44
Q
  1. Define stress (σ) experienced within a solid?
A
  • the magnitude of the force acting on the object (F)
  • divided by the area (A) over which it acts
45
Q
  1. What is the formula for stress?
A
  • σ = F/A
  • stress = Force (N) / Area (m²)
46
Q
  1. What is the SI unit for stress?
A
  • Pascals (Pa)
47
Q
  1. Define strain (ε)?
A
  • it is the fractional deformation
  • it results from a stress
48
Q
  1. How is strain measured?
A
  • it is measured as a ratio
  • it is the ratio between:
    • change in the dimension of the body
    • and the original dimension in which the change
      occurred
49
Q
  1. What is the mathematical formula for strain?
A
  • the SI unit for strain does not exist
  • this is because strain is a ratio
50
Q
  1. What is Young’s Modulus?
    How else is this modulus called?
A
  • it is the measure of the stress over the strain
  • it can also be called the Modulus of elasticity
51
Q
  1. What is the mathematical formula for Young’s modulus?
A
  • Y = σ / ε
52
Q
  1. What does a large modulus mean?
A
  • a large stress is required to produce a given strain
  • the object is rigid
53
Q
  1. What characteristic of the object determines the value of Y (Young’s Modulus)?
A
  • the material of the object
54
Q
  1. What is Young’s Modulus an important measure of?
A
  • the mechanical behaviour of materials
  • the larger the modulus, the tougher the material
55
Q
  1. What are isotropic materials?
A
  • they are materials that have the same Young’s Modulus in all directions
  • it does not matter which direction you are stretching the object
56
Q
  1. What are Anisotropic materials?
A
  • they are materials that have different Young’s Moduli in different directions
  • this is due to asymmetry in the microstructure of the material

MED 101- PHYSICS I (28 decks)

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