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Medical physics > Dynamics and muscle contraction > Flashcards

Dynamics and muscle contraction Flashcards

1
Q

What does dynamics study?

A

The relationship between the motion of bodies and the causes (forces) that generate it

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2
Q

What is newtons first law?

A

That if a body is at rest or at moving at a constant speed in a straight line it will remain at rest or keep moving in a straight line at a constant speed unless acted upon

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3
Q

2 different name for Newtons first law

A

1st principle of dynamics
Principle of inertia

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4
Q

What is newtons second law?

A

The acceleration of an object is dependent on 2 variables:
The net force acting upon the object
The mass of the object

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5
Q

How are F and a proportional?

A

Directly

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6
Q

How are m and a proportional?

A

Inversely

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7
Q

What is center of mass (COM)?

A

The point in a system that responds to external forces as if the total mass of the system were concentrated at this point
Mean position of the mass in an object

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8
Q

What is the center of gravity (COG)?

A

The point where the mass of the body is concentrated

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9
Q

When are COM and COG the same?

A

When the gravitational field is uniform across an object

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10
Q

What 3 things can forces do?

A

Impart an acceleration to a body free to move
Deform a constrained body
Rotate a body around a point (torque) if force is applied to a point of rotation

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11
Q

What does the centripetal force cause?

A

The tendency to move towards the centre

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12
Q

What does the centrifugal force cause?

A

The tendency to move straight without turning

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13
Q

What force do we feel when a car is turning?

A

The centrifugal force

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14
Q

What kind of force is centrifugal force?

A

An apparent force, it is not real

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15
Q

What kind of proportionality is there between the deformation and force applied?

A

Linear

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16
Q

2 ways to measure forces

A

Statically or dynamically

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17
Q

What kind of quantity is force?

A

Derived

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18
Q

What is the difference between the Kg weight and the mass?

A

Mass is constant, Kg weight depends on force

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19
Q

What is the relative density?

A

The ratio between the mass of a certain volume of a substance and the mass of an equal volume of distilled water at 4c*

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20
Q

What is the absolute density?

A

Ratio between the mass of a body and its volume

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21
Q

What is the relative specific weight?

A

Ratio of weight of a body and weight of an equal volume of distilled water at 4c*

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22
Q

What is the absolute specific weight?

A

Ratio between weight of a body and its volume

23
Q

What is the torque?

A

The vectorial product of 2 vectors

24
Q

What is Newton’s third law?

A

For every action force in nature there is an opposite and equal reaction

25
Q

What symbol defines momentum?

A

q

26
Q

Equation of momentum

A

q=m • v

27
Q

What is the electrostatic force defined by?

A

Coloumbs law

28
Q

What is the columb derived from?

A

Ampere

29
Q

What are the 2 properties of matter?

A

Charge
Mass

30
Q

Formula for centripetal acceleration

A

v^2/r

31
Q

What is restoring force in SHM?

A

Force that brings the body back to the center of oscillation

32
Q

What composition does fast animals tend to have?

A

Long, light limbs and powerful muscles

33
Q

How do you change m/s into km/h?

A

Multiply by 3.6

34
Q

What is the speed of the animal directly proportional to?

A

Muscle strength
The extent of the contraction

35
Q

What do muscles convert chemical energy into?

A

Mechanical work

36
Q

What is the efficiency of muscle always?

A

Less than 100%

37
Q

2 types of muscle contraction

A

Isotonic
Isometric

38
Q

What is isotonic muscle contraction?

A

When muscle is performing work against an external force (shortens or stretches)

39
Q

What is isometric muscle contraction?

A

When muscle contracts to balance and external force but neither lengthens or shortens

40
Q

What happens during isometric contraction?

A

Muscle doesn’t shorten
Sarcomeres shorten (generating force)
Elastic elements stretch, allowing length of muscle not to vary

41
Q

What happens during isotonic contraction?

A

Sarcomeres shorten more
Elastic elements are already stretched so entire muscle shortens

42
Q

When is the tension force (T) maximum during isometric contraction?

A

When length (L) of muscle is equal to that at rest (L0)

43
Q

What happens when the muscle is shorter or more stretched during isometric contraction than in the resting position?

A

It developed less strength

44
Q

At resting length, is the passive tension of a muscle 0?

A

No

45
Q

What happens if we cut the tendon of the muscle at resting tension?

A

It would get 20% shorter

46
Q

What does the shortening change in length (^L) depend on in isotonic contraction?

A

The load

47
Q

When is the shortening ^L in isotonic contraction equal to 0?

A

When maximum force (tension), Max is equal to the external load (F)
Tmax=Fmax

48
Q

When is the shortening ^L in isotonic contraction its maximum?

A

When the load is 0

49
Q

What kind of graph does the defence of the shortening on the load make?

A

A linear graph

50
Q

What is the external load (F) equal to during isotonic contraction when the work and power produced are maximum?

A

F=1/2*Fmax

51
Q

What is the absorbed power of muscles

A

Energy consumed in the unit of time

52
Q

What is the power produced in muscles?

A

Useful work in the unit time

53
Q

How many joules is 1 calorie?

A

1 cal = 4.184 J

54
Q
A

Medical physics (10 decks)

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