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MED 101- PHYSICS I > 4. STATICS OF THE BODY > Flashcards

4. STATICS OF THE BODY Flashcards

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1
Q
  1. What is Statics?
A
  • it is the study of Forces in Equilibrium
  • the study of bodies that are not accelerating
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2
Q
  1. What is Static Equilibrium?
A
  • it is an equilibrium that is not in motion
  • the physical state of the system, in which the components of the system are at rest and the net force acting on a system should be zero
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3
Q
  1. What does it mean when a system is in Dynamic Equilibrium?
A
  • it is in equilibrium and also in motion
  • they system is travelling at a constant velocity
  • or it is rotating at a constant rate
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4
Q
  1. What can each force be resolved into?
A
  • it can be resolved into components in the x,y and z directions
  • these directions are also known as planes
  • the vertical, horizontal and perpendicular planes
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5
Q
  1. What are these components of F?
A
  • Fx
  • Fy
  • Fz
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6
Q
  1. What is the sum of the forces (F) in each of the x,y and z directions when the object is in the static condition/equilibrium?
A
  • they are zero
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7
Q
  1. Can you write down the scientific equation to show that the sum of the Forces acting in the x,y and z directions are zero at static equilibrium/condition?
A
  • Σ Fx= 0
  • Σ Fy= 0
  • Σ Fz= 0
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8
Q
  1. Where can the forces be in balance with regards to the object/body?
A
  • they can either be in balance for the entire body
  • or for any part of it
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9
Q
  1. What is torque?
A
  • it is a physical quantity
  • it is not a force in the Newtonian sense
  • it is a moment
  • it is the tendency of a force to rotate an object about an axis, a fulcrum or a pivot
  • it is the physical quantity which causes an object to begin to rotate or move in a circle
  • or to change its rate of rotation
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10
Q
  1. What is another name for torque?
A
  • the moment of a force
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11
Q
  1. What is a fulcrum?
A
  • it is the point at which the lever pivots

PIVOT=the central point on which an object turns

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12
Q
  1. What is the symbol for torque?
A
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13
Q
  1. What components can torque be resolved into?
A
  • it can be resolved into components in the x, y and z directions
  • this is written as:
    • τx
    • τy
    • τz
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14
Q
  1. What happens to the torques about the x,y and z axes when the body/object is in the static condition/equilibrium?
A
  • the torques about the x,y and z axes sum up to zero
  • all the torques acting on the system are equal to zero in each plane
  • this is true for the entire body/object and for any part of the body/object
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15
Q
  1. Can you write down the scientific equation to show that the sum of the Torques about the x,y and z directions are zero at static equilibrium/condition?
A
  • Σ τx= 0
  • Σ τy= 0
  • Σ τz= 0
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16
Q
  1. When is a system said to be in Equilibrium?
A
  • when the net force on that system is zero
  • and the net torque on the system is also zero
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17
Q
  1. When is a system said to be in Static Equilibrium?
A
  • when it is in equilibrium
  • and also stationary
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18
Q
  1. What are three examples of Static Equilibrium?
A
  • a perfectly balanced seesaw
  • the ankle: when a person stands on their tip toes
  • the elbow joint: when a person hold an object
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19
Q
  1. When is a system in stable equilibrium?
A
  • when it returns to equilibrium after it has just been subject to a small displacement
  • when the net force and net torque acting on the object are ZERO

NET= sum of

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20
Q
  1. When is a system in an unstable equilibrium?
A
  • when it does not return to its original equilibrium after having been subject to a small displacement
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21
Q
  1. When is a system in Neutral Equilibrium?
A
  • when the object is displaced and then moves into a new position
  • when its equilibrium is independent of displacements from its original position
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22
Q
  1. When an object with a much narrower top and a broader base is placed on its top, is it more stable or unstable?
A
  • more unstable
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23
Q
  1. When an object with a much narrower top and a broader base is placed on its base, is it more stable or unstable?
A
  • more stable
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24
Q
  1. Which of these is in unstable equilibrium.
    Explain.
A
  • Object one is in unstable equilibrium
  • it has been slightly displaced
  • it is unable to return to its original position
  • it does not return to its original equilibrium
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25
Q
  1. Which of these is in stable equilibrium.
    Explain.
A
  • Object two is in stable equilibrium
  • it has been slightly displaced
  • it has returned to it’s original position
  • it has returned to it’s original equilibrium
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26
Q
  1. When is stability essential to human beings?
A
  • during standing
  • during any type of motion
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27
Q
  1. What is the criteria for overall stability during standing?
A
  • the centre of mass has to be over the area spanned by the feet
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28
Q
  1. What does the vertical line (centre of gravity) passing through the centre of mass of the person have to pass through to ensure stability?
A
  • it has to pass through the area of the support base
  • WITH REGARDS TO PEOPLE: this would be the area of ground in between the person’s feet
29
Q
  1. If a person is to be standing on the ground and spread their legs further apart, is there stability increased or decreased?
    WHY?
A
  • their stability is increased
  • because their base of support is increased
30
Q
  1. What would happen to a person if the centre of gravity did not pass through the area of their support base and their centre of mass was not above the area spanned by their feet?
A
  • their torques would not be balanced
  • they would be unstable
  • they would topple over
31
Q
  1. When the centre of the mass is above the area spanned by the feet, what is the result?
A
  • the right foot causes a - torque
  • the left foot causes a + torque
  • they torques cancel out
  • the net torque is therefore ZERO
  • the person is stable
32
Q
  1. What happens to the person when their centre of mass is to the left of the area spanned by the feet?
A
  • both feet now cause negative torques
  • the torques are unbalanced
  • the net torque is not equal to zero
  • the person is unstable
33
Q
  1. What happens to the person when their centre of mass is to the right of the area spanned by the feet?
A
  • both feet now cause positive torques
  • the torques are unbalanced
  • the net torque is not equal to zero
  • the person is unstable
34
Q
  1. When are we most stable?
A
  • when the line/centre of gravity is near the centre of the support base
35
Q
  1. What happens to the line/centre of gravity when we lean?
A
  • it can pass through the outside of the base
  • or through the outer limits/ edge of the base
36
Q
  1. What is the amount of turning/torque produced by the force applied on the object dependent on?
A
  • the magnitude of the Force (F)
  • the length of the object
  • the product of these 2 factors gives the torque
37
Q

37.What is the formula to work out Torque?

A

τ= Force x distance (distance from the pivot point)
τ= Fxd
τ=Fd

  • torque is proportional the length of the object
  • torque is proportional to the force on the object
38
Q
  1. What is the unit that torque is measured in?
A
  • Nm
  • Newtons x metres
39
Q
  1. What does the torque provide us with?
A
  • a useful way to measure the turning effect (the tendency to cause rotation) of the force applied to the object
  • this is called the moment arm
  • it can also be called the lever
40
Q
  1. What does an increased distance from the point at which the force is applied to the axis of rotation (longer lever arm) result in?
A
  • it makes it easier for the object to rotate
  • it increases the torque

NB: this distance defines the rotating ability of the force

41
Q
  1. What kind of motion causes a positive torque?
A
  • motion in the counter-clockwise direction
  • a force that causes a counter-clockwise rotation about the pivot point causes a positive torque
42
Q
  1. What kind of motion causes a positive torque?
A
  • motion in the anticlockwise direction
  • a force that causes a clockwise rotation about the pivot point causes a negative torque
43
Q
  1. What three components can the equilibrium equations be reduced to?
A
  • Σ Fx= 0
  • Σ Fy= 0
  • Σ τz= 0
44
Q
  1. What are the 3 types of levers we get?
A
  • 1st Class Levers
  • 2nd Class Levers
  • 3rd Class Levers
45
Q
  1. Is there a net torque in a system in static equilibrium?
    Why or why not?
A
  • there is not
  • all the torques are balanced
46
Q
  1. When there is no net torque, what happens to the system with regards to motion?
A
  • it remains motionless
  • this is because there is no tendency to rotate
47
Q
  1. What is the Principle of Moments?
A
  • at equilibrium, the sum of the clockwise moments are equal to the sum of the counter clockwise moments
48
Q
  1. What is the formula to represent the Principle of Moments?
A

the sum of all the negative torques=
the sum of all the positive torques

49
Q
  1. What are the characteristics of a First Class Lever?
A
  • the weight (load) and the muscle (effort) act on opposite sides of the fulcrum
  • the fulcrum (pivot point) is in the middle of the weight (load) and the muscle (effort)
  • the weight (load) and the muscle (effort) act in the same direction

NB: the weight (load) can sometimes be referred to as the Resistance

NB: the muscle (effort) can sometimes be referred to as the Applied Force

50
Q
  1. Is a First Class Lever very common in the body?
A
  • NO
  • it is the least common
51
Q
  1. Give me two examples of First Class Levers?
A
  • a seesaw
  • a head atop the spinal cord
52
Q
  1. What are the characteristics of a Second Class Lever?
A
  • the muscle (effort) and the weight (load) act on the same side of the fulcrum
  • the weight (load) is in the middle of the fulcrum and the muscle (effort)
  • weight (load) and muscle (effort) act in opposite directions
53
Q
  1. How common is a Second Class lever?
A
  • it is the second most common lever in the body
54
Q
  1. Give me 2 examples of a Second Class Lever?
A
  • a person wheeling a wheel barrow
  • going on your tip toes
55
Q
  1. What are the characteristics of a Third Class lever?
A
  • the muscle (effort) and the weight (load) are on the same side of the fulcrum
  • the muscle (effort) is in the middle of the fulcrum and the weight (load)
  • the weight (load) and the muscle (effort) act in opposite directions
56
Q
  1. How common is the Third Class Lever?
A
  • it is the most common lever in the body
57
Q
  1. Give me 2 examples of a Third Class Lever?
A
  • a tennis racket
  • holding a weight at a 90 degree angle to work your arm muscles
58
Q
  1. What are the levers, fulcrums and efforts in the human body?
A
  • Bones: lever arms
  • Joints: fulcrums
  • Muscles: provide effort
59
Q
  1. Answer the following question.
A
  • A
60
Q
  1. Answer the question.
A
  • D
61
Q
  1. Answer the question.
A
  • C
62
Q
  1. Answer the question.
A
  • B
63
Q
  1. Read through the summary.
    Does everything make sense?
A
  • yes
64
Q
  1. Read through the summary.
    Does everything make sense?
A
  • yes
65
Q
  1. Read through the summary.
    Does everything make sense?
A
  • yes
66
Q
  1. Read through the summary.
    Does everything make sense?
A
  • yes
67
Q
  1. Read through the summary.
    Does everything make sense?
A
  • yes
68
Q
  1. Provide a definition for the centre of mass?
A
  • this is the point at which the total mass of the body may be considered to be concentrated (for many proposes)
  • this is used when analysing the motion
  • the centre of mass does not require a gravitational field
69
Q
  1. Provide a definition for the centre of Gravity?
A
  • this is the point where the total weight of the material body is concentrated.
  • in a uniform gravitational field, the centre of gravity is equal to the centre of mass

MED 101- PHYSICS I (28 decks)

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