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Biomechanics > Assessment 1 > Flashcards

Assessment 1 Flashcards

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1
Q

Kinematics

A

Motion in terms of time and space How fast - velocity
How far - distance
How consistently - acceleration
With NO reference to forces

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2
Q

Kinetics

A

Examines the forces that act on a body or a system. It explains how the movement is produced

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3
Q

If no external forces are applied on a body or if the net sum of any applied external forces is ZERO, then the body’s motion remains UNCHANGED

A

If body is at rest (not moving) it will stay at rest

If the body is moving with constant velocity then it will keep moving with constant velocity

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4
Q

What is a NET force?

A

Net force is the vector sum of forces acting on a particle or body. The net force is a single force that replaces the effect of the original forces on the particle’s motion. It gives the particle the same acceleration as all those actual forces together as described by the Newton’s second law of motion.

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5
Q

Newton’s first law also know as

A

Law of inertia

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6
Q

Newton’s second law

A

Law of acceleration

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7
Q

The rate of the change of motion (acceleration) of a body is proportional to the force acting on it and is in the direction that the force acts

A

F=M A
F = force
M = mass
A = Acceleration

1 Newton is the amount of force necessary to accelerate a mass of 1 kg at 1m/sec2

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8
Q

Law of acceleration

Rules

A

The greater the force the greater the acceleration

The greater the mass (of the object being moved)the harder it is to produce a given acceleration

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9
Q

Newton’s 3rd law

A

Law of action-reaction

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10
Q

Law of action reaction

A

For every action there is an equal and opposite reaction

For every force that is exerted there is an equal and opposite force exerted by the second body on the first

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11
Q

3rd law implications on sport

A

To maximise ground reaction forces we need to have a suitable body position

Note runners positioning
Rugby scrum etc

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12
Q

Practical example

A

Jumping in a lift when blindfolded to tell if you were going up or down.

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13
Q

Law of gravity

A

Every particle on the universe attracts every other particle with an attractive force

F=G m1 m2 / 10-11

G - universal constant = 6.67 x10-11
M1,m2 - masses of the two objects
R - distance between two objects

According to equation - the longer the distance between objects the smaller the attractive force

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14
Q

As the constant G is very small, the force between two cricket balls (mass = 158kg) 5m apart will also be very small

A

F=G m1 m2 / r2
F = 6.67 x 10-11 x0.158 x 0.158/5squared

F= 6.67 x 10-14N

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15
Q

According to the law the weight of an object on the earths surface will be

A

W = G m(earth)m(object)/r(squared)

R is the distance from the centre to the surface of the earth
Assuming distance is always the same then the fixed gravitational acceleration for any object on earths surface would be

g= Gm(earth)/r(squared)=9.81m/sec(squared)

This the weight of any object would be

W = m g

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16
Q

What is the effective value of gravity 1000km above earth’s surface? Radius of earth = 6380km and mass of earth = 5.98 x 10(power of 24) kg

A

G = g m earth / r(squared)

G = 7.32m / sec(squared)

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17
Q

Inertia

A

The resistance of a body to changes in its motion

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18
Q

In linear motion

A

Inertia of a body is measured by its mass. The more massive a body the greater its inertia

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19
Q

Mass is…

A

The quantity of matter a body possesses

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20
Q

Mass is NOT the same as weight

A

Weight is the force

Mass is not a force

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21
Q

Weight - centre of gravity

A

Bodies are composed of a large number of particles. Each particle experiences an attraction towards the centre of the earth. The sum of all these attractive forces is the weight of a body

W= m g

In biomechanics it is inconvenient to consider the force acting on every particle of a body. Therefore, we replace all the little forces with one resultant force that has the same effect

This resultant Force is considered to be acting on the centre of gravity of the body

The cg is of interest because a body behaves as though all of its mass were concentrated at the cg

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22
Q

What would an 80 kg person weigh on the moon?

What would their mass be on the moon
Gravity on the moon is 1.57 m.s-2

A

Weight

W= mg
80 x 1.57
= 125.6N

Mass is still 80kg on the moon.
Mass is not a force and not the same as weight

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23
Q

Forces

Study These Flashcards
A

Internal/external
Contact/ non-contact
Concentric/ eccentric

24
Q

External forces

Study These Flashcards
A

Act on objects as a result of interaction with the surrounding environment

25
Contact or surface forces occur between
Objects in contact ``` Fluid forces (air and water) Reaction forces with another body (ground, implement) ```
26
Non-contact forces occur even if objects
Are not touching each other
27
Internal forces
Act WITHIN the object or system whose motion is being investigated Action/ reaction forces both act on different parts of the system Do not accelerate the body Orientate segments Maintain structural integrity
28
Kinetic force data are useful for performance enhancement and injury prevention
Force plates are sophisticated measuring scales embedded in the ground
29
They measure the ground reaction forces generated when body is in contact with the plates
Ie no explicit information on the internal forces acting between body segments
30
How do plates work?
The measurement of the force is done by applying Newton’s 3rd law (action reaction) The force plate transducers concert the force exerted on it into an electrical signal The applied ground reaction forces (grf) are vectors and can be broken down into 3 components
31
Force platform applications
Often used in conjunction with video analysis to link kinetics and kinematics Applications for Performance enhancement Equipment design (shoes etc) Injury prevention rehab
32
Concentric forces
A force whose line of action passes through the CoG of the body on which it acts is called a concentric force A concentric force causes a change in linear motion but no changes in angular motion ( rotation)
33
Eccentric forces
A force whose line of action does not pass through the CoG of the body on which it acts is called an eccentric force An eccentric force causes changes in both angular and linear motion
34
Force couples
Equal, opposite directed and parallel forces constitute a force couple. A force couple tends to cause rotation only
35
Vectors
Have both magnitude and direction ``` Displacement Velocity Acceleration Force momentum Drag Lift Weight Lift ```
36
Scalar
Only have magnitude ``` Length Area Volume Mass Density Pressure Temperature Work Power ```
37
Adding scalars | Simply add the amounts
F1 rules state the car and driver should be a minimum of 702kg. If Lewis Hamilton is 68kg and loses 2kg of sweat during the race, what is the minimum mass his car needs to have before he starts the race???
38
Triangle rule | Adding vectors
Obtain the resultant by drawing just the two vectors in head to tail fashion and then forming the resultant by connecting the tail of the 1st vector to the top of the 2nd
39
Parallelogram law
The sum of two vectors, called the resultant, is equal to the diagonal of the parallelogram that has sides equal to the two vectors
40
adding vectors steps
Locate starting point Draw first vector starting point from the tail Start the tail of the next vector at the head of previous one Repeat until all vectors are added The resultant is then drawn form the tail of the firs vector to the head of the last vector
41
Vector resolution
Any vector can be decomposed into an arbitrary set of vectors that will add up to the original vector In sports you often know the resultant and are required to determine the components
42
Vector analysis | Key trig equations
SOH CAH TOA Sin - opposite/ hypotenuse Cos - adjacent/ hypotenuse Tan - Opposite/ Adjacent Pythagoras Theorem a2 + b2 = c2
43
Vector analysis example
If discus is thrown at 0=30 degrees and we know that the horizontal face (adjacent) in 100N, find the vertical force (opposite) and the resultant Force (hypotenuse) ``` Use 1) cos0= adj/hyp; Cos30= 100/hyp 0.866 = 100/hyp Hyp = 100/0.866 Hyp = 115.47N (resultant Force) ``` ``` 2) tan0= opp/adj Tan30= opp/100 0.577 = opp/100 Opp= 0.577 x100 Opp = 57.74 N (vertical force) ```
44
Free body diagrams
I’m human movement several forces might act on a body simultaneously. A graphical representation of these forces can enhance our understanding of the forces and facilitate subsequent calculations FBD show all external forces acting on a body (or object, system) In FBD, forces are drawn as vectors, with the size and direction of the arrow reflecting those of the force. The tail is normally placed at the force’s point of application The force vectors should attach to the body at the point at which they act
45
Drawing FBD
Isolate the body (object, system) from its surrounding Identify each external forces acting and draw the vectors with the correct size and direction Select a coordinate system for the purpose of identifying positive and negative forces
46
Stability and mobility
Bodies are composed of a large number of particles. Each particle experiences an attraction towards the centre o the earth. The sum of all these attractive forces is the weight of a body Why consider the centre of gravity It is inconvenient to consider the force acting on every particle in a body. Therefore, we replace all the little forces with one resultant force that has the same effect
47
Why consider position of CG for humans
Because the body behaves as though all of its mass were concentrated at CG For example when the human body acts as projectile it follows a parabolic path, regardless of any changes of body configuration
48
Practical example CG
Assume you are jumping vertically for maximum height during a jump and reach test. Once airborne what can you do to maximise performance Use arms for momentum
49
Stability and equilibrium
Equilibrium describes the state of a system that is not changing its speed or direction Newton’s 1st law Equilibrium can exist for a body at rest, this is called static equilibrium For a body that has unchanging speed or direction, this is called dynamic equilibrium
50
Stability and equilibrium
The stability of a body refers to the state of equilibrium or state of balance of a body. It can be defined as the ability of a body to maintain its beginning static equilibrium posture A body in equilibrium may be in either stable, unstable or neutral equilibrium Stable equilibrium implies that if a small perturbation is applied to an object then it tends to return to its original position Eh boxing bag child punching
51
Unstable equilibrium
Implies that if a small perturbation is applied then It tends to accelerate away from its original position Balance beam, handstand
52
Neutral equilibrium
Implies that an object neither returns nor accelerates away from its original position after a small perturbation Ball lying on the ground
53
Base of support
The base of support is a critical variable in considering balance and stability. It is defined as the area made with part of the body ruching the supporting surface
54
Factors affecting balance
Height of CoG with respect to base of support Location of the line of gravity relative to the base of support Mass of the athlete Teaching implications for balance activities Start with low CoG and wide bases of support. Progress to smaller bases of support and higher CoG as confidence and skill increases
55
Stability against perturbing forces
The line of gravity must project down into the base of support to ensure stability What shall we do to increase stability against a perturbing force ? Move the line of gravity towards the edge of the base of support in the direction of the oncoming force
56
Mobility
To initiate quick movement, move to a position in which CoG is close to perimeter of the base of support
57
Stability of the body refers to its state of equilibrium/ balance
Stable - returns to original position Unstable - accelerates away from original position Neutral - does neither of the above

Biomechanics (1 decks)

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