6. KINEMATICS (STANDING, RUNNING AND WALKING) Flashcards
1
Q
- What is Kinematics?
A
- it is a branch of mechanics
- it deals with the motion of bodies
- it does not consider mass or force
2
Q
- What does Kinematics involve?
A
- it involves tracking the motion of the centre of mass of the body
- it involves tracking the angle vs the time
-it involves tracking the angle versus the angle - this is all tracked during the walking or running cycle
- the three angles that are tracked are:
- the angle of the thigh
- the angle of the knee
- the angle of the ankle
3
Q
- What are the angles changed by?
A
- they are changed by the forces
- these forces are controlled by different muscles
4
Q
- What is the criteria for overall stability during standing?
A
- the centre of mass has to be over the area spanned by the feet
- the vertical line passing through the centre of mass has to pass through the area of the support base
5
Q
- What do stable joints indicate?
A
- local stability
6
Q
- What is the formula for working out pressure?
A
- P= F/A
- Pressure = force divided by area spanned
7
Q
- What is the SI unit for pressure?
A
- Pascals (Pa)
- this is known as a Newton per square metre (N/m2)
(kg.m⎺¹.s⎺²)
8
Q
- How would you work out the pressure on the feet of a 71kg person?
A
- 71kg x 9.81 = 700N
- 700N / 2 = 350N per foot
- Total cross-sectional area of the two feet= 350cm²
- 350cm² / 100² = 0.035m²
- Pressure = F / A
= 700 / 0.035
= 20 000 Pa
9
Q
- What is the relationship between Pressure and area?
A
- they are inversely proportional
- pressure is decreased when the area increases
10
Q
- Does your whole foot touch the ground when you are standing?
A
- no
- most of the contact is at the ball and the heel of each foot
11
Q
- What is higher on the ball and the heel of each foot?
A
- the pressure
- it is almost 5x higher
12
Q
- What is higher on the feet and why?
A
- the peak forces (pressure) are higher on the feet during walking
- this is because only one foot is on the ground at a time
- this means that there is a smaller area being spanned
- this results in a higher pressure
(pressure on the feet that is exactly 2x higher than
the pressure on the feet during standing) - the force on the foot is twice that than with both feet on the ground
13
Q
- What are the normal forces involved in with regards to walking?
A
- braking
- forward repulsion
14
Q
- What changes with the magnitude of the normal forces during walking?
A
- they are two times greater than the magnitude of the normal forces during standing
15
Q
- What makes the contact area between the ground and the foot much less during walking?
What does this result in?
A
- the whole foot is not flat on the ground during most phases of walking
- this increases the peak-pressure during walking to be 30 times higher than during standing
16
Q
- How are routinely force plots measured?
A
- they are measured during motion
- they make use of pressure sensors
17
Q
- What are the multiple bones in the human foot suspended by?
A
- they are suspended by a series of muscles and ligaments
18
Q
- What does the suspension of the muscles and the ligaments form?
What is the function of this?
A
- it forms the foot arch
- this arch assists in stability during standing
- it helps with walking
- it allows movement to be a low energy consuming activity
19
Q
- What happens when the foot hits the ground?
A
-the arch flattens
- as the arch restores:
- the foot is propelled forward by the toes
20
Q
- What are the disadvantages of bipedal movement?
(spreading the weight on two feet instead of four?
A
- tendency to cause lower back pain
- sprained ankles
- knee problems
21
Q
- What is the similarity between the kinematics, forces and energetics of walking and running?
A
- in both walking and running:
- the foot pushes back to get a forward reaction force
- the normal force is always acting upwards on the foot
22
Q
- Why is it harder to walk in sand?
A
- there is a small reaction force on the feet until the sand is compressed
(this is indicated by your footprints)
23
Q
- How do your footprints in the sand look?
A
- they are deeper in the front than at the heel
- this is because the foot is pushing off (backwards) in the sand
- there is a stronger force
- this produces more pressure
24
Q
- What are the 7 stages of walking?
A
- Heel Strike (initial contact)
- Loading Response (foot is flat)
- Mid Stance
- Terminal stance (heel is off)
- Pre swing (toe is off)
- Initial and Mid-swing
- Terminal swing
25
25. What are the two time periods that the hip, knee and ankle angles are usually related to?
1. When the foot touches the ground (FS)
- this is known as the Foot Strike
- it is also known as the heel strike/contact
2. When the toes leave the ground (TO)
- this is also known as the toe off
- it is also known as the foot off
26
26. What is the stance phase?
- this is the phase found between the foot strike
(when the foot touches the ground)
AND the toe off
(when the toes leave the ground)
27
27. What is the swing phase?
- this is the phase found between the toe off
(when the toe leaves the ground)
AND the foot strike
(when the foot touches the ground)
28
28. When does the stance phase occur for walking?
- during the first 60%-65% of the cycle (Gait Cycle)
29
29. When does the swing phase occur for walking?
- during the last 35%-40% of the cycle
30
30. When are there two feet in the ground during the gait cycle for walking?
- during the first 10%
(just after the foot strike)
- during the last 10%
(just before the toe off)
OF THE STANCE PHASE
31
31. Are both feet ever on the ground at the same time?
- NEVER
32
32. What is the Kinetic energy of the body dependent on?
- it depends on the objects mass
- it depends on the speed of its centre of mass
33
33. What can the total Kinetic Energy be split up into?
- it can be split into:
- the kinetic energy due to motion in the horizontal plane
(the x axis)
- the kinetic motion due to motion in the vertical plane
(the y axis)
34
34. What is the formula for the total Kinetic Energy?
KE= KE horizontal + KE vertical
= (½ x m x v²) horizontal + (½ x m x v²) vertical
NB: your focus is on the initial velocity
35
35. What is the formula for the potential energy?
PE = mgh
= mass of the body x gravity x the length on the y axis
36
36. How do we describe a system where the energy is not supplied or lost?
- we describe the total energy of the system as constant
- this energy does not increase or decrease
- this is because the total energy of the system is conserved
37
37. What is the formula for the total constant energy?
- E = KE + PE
38
38. Is the total energy completely constant during walking?
- no
- it is almost constant
39
39. How long is each foot on the ground for during running?
- it is on the ground for less than half the time
- sometimes neither foot is on the ground
40
40. Describe the running process?
- the runner starts in a four-point stance
- they then push off of the starting block with both legs
- this gives them forward acceleration
- the body is fairly horizontal at first
(this is to keep pushing the runner forward)
- the runner than accelerates as fast as possible
- the body becomes vertical to increase the stride length
- this helps to reach and maintain maximum speed over the finish line
41
41. What is one difference between walking and running?
- the leg becomes almost straight during walking
- it never does this during running
42
42. Which % is higher during running, the stance or the swing?
- the swing % is greater during running
43
43. When and in what quantity does the stance occur?
- the stance occurs during the first 40% of the gait cycle
- this is after the foot strike
44
44. When and in what quantity does the swing occur?
- it occurs during the next 60% of the gait cycle
- this when the foot is off the ground
- this is from the toe off to the next foot strike
45
45. Which other limbs move during running?
- your arms swing back and forth
- your torso rotates
- both are 180° out of phase with your legs
46
46. What does the height of your jump depend on?
- how fast you can take off
47
47. What are the 4 stages of a vertical jump?
1. standing
2. crouch
3. take-off
4. free-flight
48
48. What happens to the centre of mass when the person crouches?
- it decreases
49
49. What happens to the centre of mass when the person takes off?
- it increases
50
50. What is the speed of the person at the top of the Free Flight phase?
- it is 0m.s⎺¹
51
51. When does the extension phase start and end?
- it starts after the crouch
- it ends before the take-off
52
52. What happens to the centre of mass and the velocity of the person during the extension phase?
- the centre of mass rises by the distance between the centre of mass and the hip joint
- the velocity equates to the velocity of the take off from the ground
53
53. What happens to all the kinetic energy at takeoff?
- it is converted to potential energy at the top of free flight
- this means that the mechanical energy is conserved
- this means that we need to use the mechanical energy formula when doing equations on this topic
(ME= KE + PE)
54
54. What formula can you use to work out the vertical height achieved by the person that is jumping?
(when velocity is given)
H = v² (of the take off)
_______________
2g(9.81)
55
55. What formula can you use to work out the vertical height achieved by the person that is jumping?
(when time and distance is given)
H = 2 x (distance) ²
_______________
g x (time) ²
56
56. What is the mathematical relationship between extension time and the height of the jump?
- the height of the jump is greater when the time is decreased
- the two are inversely proportional
57
57. What do both legs generate during extension?
- they both generate a normal force
- these two FN forces together make up the net force
(total vertical force)
58
58. Read Summary one.
Does everything make sense?
- yes
59
58. Read Summary one.
Does everything make sense?
- yes
60
60. Read Summary three.
Does everything make sense?
- yes
61
61. Read summary four.
Does everything make sense?
- yes
62
62. Read summary five.
Does everything make sense?
- yes
