MNSR.10

Question 1

What is the centre of gravity?

Answer 1

The point of an object where all of the weight acts from

Question 2

What does centre of gravity move in accordance with?

Answer 2

Newton’s simple laws of motion

Question 3

Where is the CoG located for uniformly dense and symmetrical objects?

Answer 3

At their geometric centres

Question 4

Where does the vast majority of your body weight sit?

Answer 4

Between your head and knees (trunk)

Question 5

Where is the CoG located for non-uniformly dense and non-symmetrical objects?

Answer 5

Can be outside or off centre of the body

Question 6

Where is the CoG located for irregular shapes?

Answer 6

Suspend the object, attach a plumb line to it(a string with a weight on one end…shows line of gravity), re-suspend and repeat. Where the two lines intersect is the CoG

Question 7

Stability, if weight is centred between the 2 supports?

Answer 7

The torques about the CoG due to the reaction forces (R1 and R2) are equal and opposite, therefore the cancel out. Stable

(R1xL1) = (R2xL2)

Question 8

Stability, if CoG is to the left of the 2 supports?

Answer 8

The torques about the CoG are in the same direction, so the net torque isn’t 0 and the beam becomes unstable and topples over

(L1xR1) + (L2xR2)

Question 9

What makes objects more stable?

Answer 9

The lower the CoG and the bigger the base area, the greater the stability

Question 10

Examples of stable activities?

Answer 10

Standing, walking, or leaning. Where the CoG lies inside the area of support

Question 11

Examples of unstable activities?

Answer 11

Activities where the CoG lies outside of the area of support

Question 12

What changes our posture?

Answer 12

Daily activities and age

Question 13

Why does age affect posture?

Answer 13

As you age, the weight of your head doesn’t change, the your muscle’s response to it does. Lose muscle mass as we age, so it doesn’t have that same ability as before

Question 14

What are 3 issues that can arise if poor posture isn’t corrected?

Answer 14

• Back pain
• Muscle fatigue
• Headaches

Question 15

Scoliosis?

Answer 15

• An abnormal curvature in the spine (S or C shaped)

Question 16

Why do women experience back pain with pregnancy?

Answer 16

• Due to a forward shift in their CoG
• Can create torques, which cause excess stress on the spine and lower backs
• The CoG also shifts higher, which increases strain on the muscles and ligaments supporting the vertebral column

Question 17

What happens to the CoG of an amputee and what effect does it have on their stability?

Answer 17

• Their CoG shifts due to the removal of a leg
• Depending on how severe their amputation (both legs, above the knee, etc) determines the severity of the instability
• The more severe the amputation, the more unstable the person is

Question 18

What is the purpose of prosthetics?

Answer 18

To correct the shift in CoG, bringing back stability to the person