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MED 101- PHYSICS I > 7. COLLISIONS OF THE HUMAN BODY > Flashcards

7. COLLISIONS OF THE HUMAN BODY Flashcards

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1
Q
  1. What is linear momentum?
A
  • it is the mass of the object times by the velocity of the object
  • the symbol for linear momentum is p
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2
Q
  1. What is the formula for linear momentum?
A

p = m x v
= mass x velocity

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3
Q
  1. How does Newton’s Second Law relate to linear momentum?
A
  • Newton’s Second Law states:
    F= m x a
  • acceleration can be calculated by:
    a = ▵v / ▵t
  • Newton’s Second Law can be rewritten as:
    F = m (▵v) / ▵t
    F = ▵ (mv) / ▵t
    F= ▵p / ▵ t
    ▵p = F x ▵t
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4
Q
  1. What is Impulse?
A
  • it is the product of the net force and the contact time

  • it is the change in momentum
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5
Q
  1. How is Impulse calculated?
A

▵p = F x ▵ t

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6
Q
  1. What is Newton’s Second Law in terms of momentum?
A
  • the net force acting on an object is equal to the rate of change of momentum

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7
Q
  1. What does Newton’s Third Law state?
A
  • there is an equal and opposite force for every force
  • forces occur in force pairs
    (action-reaction pairs)
  • these force pairs are always equal in magnitude to each other
  • the always act in the opposite direction of one another
  • these forces never act on the same object
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8
Q
  1. How can Newton’s Third Law be related to momentum?
A
  • when the momentum of one object changes,
    the momentum of another object will be
    changing by exactly the opposite amount
  • Newton’s Third Law requires that the momentum be conserved
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9
Q
  1. What is the Law of Conservation of linear momentum?
A
  • the total linear momentum of an isolated system remains constant
  • this linear momentum is conserved
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10
Q
  1. What is the formula for the Conservation of Linear Momentum?
A

p final = p initial

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11
Q
  1. What tends to happen to human beings when we collide with objects?
A
  • we break down
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12
Q
  1. What happens if an object is travelling at a constant acceleration for a given time?
A
  • the velocity changes
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13
Q
  1. What formula accurately shows how to work out final and initial velocity?
A
  • vf = vi + at
  • final velocity= initial velocity + (acceleration x time)
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14
Q
  1. What is an equation to work out the distance travelled by an object?
A
  • ▵x = (vi.t) + (½. a. t²)
  • distance = (initial velocity x time)
    + (½ x acceleration x time²)
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15
Q
  1. What is a simplified formula for finding the acceleration of an object during a collision?
A
  • a = vf-vi / total time of the collision
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16
Q
  1. How would you work out the force felt by the object during the collision?
A
  • F = m x a
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17
Q
  1. Which kinds of situations of motion are totally inelastic?
A
  • when the object decelerates to zero
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18
Q
  1. What are sticky or totally inelastic collisions?
A
  • this is when two objects collide
  • they then stick together after the collision
  • they move off together
  • they share a common velocity after the collision
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19
Q
  1. What is an inelastic collision?
A
  • this is a collision where only momentum is conserved
  • object deformation or heat is produced
  • there is a loss of kinetic energy
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20
Q
  1. What is an elastic collision?
A
  • a collision where both kinetic energy and momentum are conserved
  • the total kinetic energy is unchanged by the collision
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21
Q
  1. What happens in a totally elastic or partially elastic collision?
A
  • the objects bounce back
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22
Q
  1. During which collision is there the greatest loss of kinetic energy?
A
  • when the two objects stick together after the collision
  • this is called a completely inelastic collision
23
Q
  1. What does a compressive force have the greatest effects on?
A
  • the thinnest bones
  • these absorb the impact
24
Q
  1. What is the equation for pressure?
A

P = F/ A
= the force per unit area

25
Q
  1. What is the unit for pressure?
A
  • Pascals (Pa)
  • we usually use MPa for pressure equations of the body
  • this is the pressure times by 10⁸
26
Q
  1. Upon compression, at approximately which pressure do bones typically break?
A
  • 170 MPa
27
Q
  1. What is the measurement of the pressure at which bones break called?
A
  • the damage threshold
  • it can also be known as the ultimate compressive stress
28
Q
  1. What is another form of writing the Pressure equation (in terms of collisions)?
A
  • P = m x vi / A x t
    = mass x initial velocity / area x duration of the collision
29
Q
  1. How can the effect of the pressure on the body be reduced?
A
  • the duration (t) of the collision can be increased
  • the area of contact (A) can be increased
30
Q
  1. What are three ways to increase the collision time?
    (duration of the collision)
A
  1. Better padding
    • use better padding at the site of the collision
    • EG: wear better sneakers
  2. Increase the duration of the impact
    • adjust your body during the actual impact
    • EG: letting your knees bend during the impact after you
      have jumped
  3. Rolling over
    EG: this can be done at the end of a parachute jump
    : this increases the impact area (A)
    jump
31
Q
  1. What determines the survivability of crashes of the human body?
A
  • what part of the body makes contact
  • what type of surface it hits
  • the deceleration time
32
Q
  1. During whole body impacts, what determines your fate?
A
  • the part of the body which makes contact:
    - the back (supine position)
    - the front (prone)
    - the side (lateral)
33
Q
  1. What exactly happens during an injury to the head?
A
  • In direct trauma:
    - the head hits an object
    - the skull can fracture
  • the brain hits the interior of the skull:
    - this leads to bruising on the brain (a contusion)
    - or leads to brain bleeding (a haemorrhage)
  • In addition to the primary impact (the coup):
    - the brain can bounce off the skull
    - it can hit the back of the skull (the countrecoup)
34
Q
  1. What is indirect trauma to the brain?
A
  • this is when the brain is subject to large accelerations
    (even without impact)
  • this can lead to severe injury
35
Q
  1. What happens in Inertia injuries?
A
  • the nerve cells axons are damage by stretching
  • EG: Shaken Baby Syndrome
    : Whiplash
  • this is an effect of rotational accelerations and decelerations
36
Q
  1. How is the gravity of inertia injuries qualitatively described?
A
  • it is described by the Abbreviated Injury Scale (AIS)
37
Q
  1. What determines the severity and the likely fatality of head injuries?
A
  • guidelines
  • these guidelines are determined from the records of past accidents
38
Q
  1. What is the name of the guideline to asses severity and likely fatality of head injuries?
A
  • the Gadd Severity Index (GSI)
39
Q
  1. What does your foot experience every time is touches the ground?
A
  • a collision
40
Q
  1. What is the magnitude of the forces on the foot during a very slow step?
A
  • the forces slowly build up from 0 to mbg
  • mbg= the mass of the body x the gravitational
    acceleration (9.81)
41
Q
  1. What is the magnitude of the forces on the foot during running?
A
  • the foot reaches a peak of approximately 2.0 - 3.6 mbg
42
Q
  1. Which parts of the leg feel the initial impact of the collision with the foot and the ground?
A
  • the foot
  • the lower leg
  • the thigh
43
Q
  1. What is the formula we use when two objects collide and then move off together afterwards?
A

(ma.va)i + (mb.vb)i = (ma + mb)vf

  • if the object is stationary:
    • then vi= zero
44
Q
  1. What is the formula we use when two objects collide and rebound?
A

(ma.va)i + (mb.vb)i = (ma.va)f + (mb.vb)f

  • remember to put positive and negative signs for objects going in different directions
45
Q
  1. What is the formula we use when an object is dropped vertically on a moving object?
A

(ma.va)i + (mb.vb)i + (ma + mb)vf

  • the vi of the dropped object is zero
46
Q
  1. What is the formula we use if there is an explosion?
A

(ma+mb) vi = (ma.va)f + (mb.vb)f

  • any stationary object has a vi of zero
  • take opposite directions into account
47
Q
  1. What formula do we use when two objects are connected to each other by springs?
A

(ma + mb) vi = (ma.va)f + (mb.vb)f

  • the initial velocity is usually zero
  • take into consideration the opposite directions
48
Q
  1. What formula do we use when a bullet is being shot out of a gun?
A

(mg + mb) vi = (mg.vg)f + (mb.vb)f

  • initial velocity is usually zero
  • take into consideration the opposite directions
49
Q
  1. Read through summary.
    Does everything make sense?
A
  • yes
50
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes
51
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes
52
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes
53
Q
  1. Read through this summary.
    Does everything make sense?
A
  • yes

MED 101- PHYSICS I (28 decks)

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