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
Q
- What are the two time periods that the hip, knee and ankle angles are usually related to?
A
- When the foot touches the ground (FS)
- this is known as the Foot Strike
- it is also known as the heel strike/contact - When the toes leave the ground (TO)
- this is also known as the toe off
- it is also known as the foot off
26
Q
- What is the stance phase?
A
- 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
Q
- What is the swing phase?
A
- 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
Q
- When does the stance phase occur for walking?
A
- during the first 60%-65% of the cycle (Gait Cycle)
29
Q
- When does the swing phase occur for walking?
A
- during the last 35%-40% of the cycle
30
Q
- When are there two feet in the ground during the gait cycle for walking?
A
- during the first 10%
(just after the foot strike) - during the last 10%
(just before the toe off)
OF THE STANCE PHASE
31
Q
- Are both feet ever on the ground at the same time?
A
- NEVER
32
Q
- What is the Kinetic energy of the body dependent on?
A
- it depends on the objects mass
- it depends on the speed of its centre of mass
33
Q
- What can the total Kinetic Energy be split up into?
A
- 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
Q
- What is the formula for the total Kinetic Energy?
A
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
Q
- What is the formula for the potential energy?
A
PE = mgh
= mass of the body x gravity x the length on the y axis
36
Q
- How do we describe a system where the energy is not supplied or lost?
A
- 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
Q
- What is the formula for the total constant energy?
A
- E = KE + PE
38
Q
- Is the total energy completely constant during walking?
A
- no
- it is almost constant
39
Q
- How long is each foot on the ground for during running?
A
- it is on the ground for less than half the time
- sometimes neither foot is on the ground
40
Q
- Describe the running process?
A
- 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
Q
- What is one difference between walking and running?
A
- the leg becomes almost straight during walking
- it never does this during running
42
Q
- Which % is higher during running, the stance or the swing?
A
- the swing % is greater during running
43
Q
- When and in what quantity does the stance occur?
A
- the stance occurs during the first 40% of the gait cycle
- this is after the foot strike
44
Q
- When and in what quantity does the swing occur?
A
- 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
Q
- Which other limbs move during running?
A
- your arms swing back and forth
- your torso rotates
- both are 180° out of phase with your legs
46
Q
- What does the height of your jump depend on?
A
- how fast you can take off
47
Q
- What are the 4 stages of a vertical jump?
A
- standing
- crouch
- take-off
- free-flight
48
Q
- What happens to the centre of mass when the person crouches?
A
- it decreases
49
Q
- What happens to the centre of mass when the person takes off?
A
- it increases
50
Q
- What is the speed of the person at the top of the Free Flight phase?
A
- it is 0m.s⎺¹
51
Q
- When does the extension phase start and end?
A
- it starts after the crouch
- it ends before the take-off
52
Q
- What happens to the centre of mass and the velocity of the person during the extension phase?
A
- 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
Q
- What happens to all the kinetic energy at takeoff?
A
- 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
Q
- What formula can you use to work out the vertical height achieved by the person that is jumping?
(when velocity is given)
A
H = v² (of the take off)
_______________
2g(9.81)
55
Q
- What formula can you use to work out the vertical height achieved by the person that is jumping?
(when time and distance is given)
A
H = 2 x (distance) ²
_______________
g x (time) ²
56
Q
- What is the mathematical relationship between extension time and the height of the jump?
A
- the height of the jump is greater when the time is decreased
- the two are inversely proportional
57
Q
- What do both legs generate during extension?
A
- they both generate a normal force
- these two FN forces together make up the net force
(total vertical force)
58
Q
- Read Summary one.
Does everything make sense?
A
- yes
59
Q
- Read Summary one.
Does everything make sense?
A
- yes
60
Q
- Read Summary three.
Does everything make sense?
A
- yes
61
Q
- Read summary four.
Does everything make sense?
A
- yes
62
Q
- Read summary five.
Does everything make sense?
A
- yes
