KAAP 426 Exam 4

20 kg

Which is more stable?

The wider one on the left

Which is more stable?

The right one because it is denser at the bottom

Which one is more stable?

1. Increase the mass of the object

2. Increase the base of support

3. Lower the center of gravity position

What are 3 mechanical factors that can increase stability?

Its CG must be moved beyond the base of support

What must happen in order to topple an object?

1. Decrease the pushing force magnitude

2. Lower pushing force location (reduces moment arm)

3. Increase mass

4. Increase d (mass to point of rotation)

What are ways to become more stable (to not topple over)?

Work

Force x Distance

it gains or loses energy

What happens to an object when work is done on it?

Center of Gravity

What does "CG" stand for?

CG

The point where an object's weight is considered to act.

Yes

Does an object in the air have PE?

No

Does an object on the ground have PE?

The change in height of the center of gravity when the object is tipped

What does Δh represent in the context of tipping objects?

No, it's the same for heavy and light objects

Is the change in CG height (Δh) different for heavy and light objects when tipping?

Large

For a heavier object, is the change in potential energy when tipping large or small?

More, because it has more PE to overcome

Does a heavier object require more or less work to tip over?

More stable, because more work is required to tip it over.

Does a heavier object tend to be more or less stable? Why?

Small, because the object has a smaller mass

For a lighter object, is the change in potential energy when tipping large or small?

Less stable, because more work is required to tip it over

Does a lighter object tend to be more or less stable?

base of support

The area beneath an object that is in contact with the ground, supporting its weight.

The CG has to move a large distance (large Δh) to topple the object.

What happens to the center of gravity (CG) height change when an object with a wide base is tipped?

It increases due to a larger mass

How does the potential energy change for an object with a wide base when tipping?

Not much change in CG height to topple

What happens to the CG height when an object is toppled from a high starting point?

Large change in potential energy because of the increased height

How does potential energy change when an object with a high CG is toppled?

Little work required

How much work is required to topple an object with a high CG?

Lower CG position because more work is required to topple

Which is more stable: an object with a high or low CG?

Not a big change in CG height

How much does the CG height change to topple a high CG object?

Little change in PE

How does potential energy change when a high CG object is toppled?

more stable

Large angular displacement

Less stable

Small angular displacement

Torque

What causes rotation about the edge of the base of support of an object?

Torque equation

Force x distance from pivot

More torque is required to rotate the object to its toppling point

What does a wider base or lower CG mean in terms of Torque?

Less torque is required to rotate the object to its toppling point

What does a Narrow base or Higher CG mean in terms of Torque?

CW and CCW Torques

must be larger to rotate the object through the angular displacement to instability.

The CG must rise a larger vertical distance to reach the topppling point, so more PE is required

Wider base / lower CG relationship to PE

THE CG has a smaller vertical displacemnt so a smaller change in PE

Narrow base / high CG relationship to PE

Mass

Heavier objects → more PE change for the same CG displacement → harder to tip.

Base of Support

Wider base → larger angular displacement → larger torque & PE needed → more work.

CG height

Lower CG → increases angular displacement → more torque & more work required → more stable

Vertebrae

7 cervical, 12 thoracic, 5 lumbar

intervertebral discs

allow for slexion and extension

-Nucleus pulposus

-Annulus fobrosus

Muscular Attachment

The spinous process increases the moment arm about the axis of rotation

-Less muscle force is needed to produce a moment (smaller muscles, less bone force)

Nucleus pulposus

resisting compressive loading, gel-like mass in the center of disc

Annulus Fibrosus

capable of resisting both tensile and compressive loading, fibrocartilaginous material

Torsional Loading

Spinal rotation generates shear stress on intervertebral discs

Degenerative discs

With age

-Lose the ability to retain water

-Integrity declines

-Distribution of load changes

Kyphotic

upper thoracic/lower cervical regions

Lordotic

lumbar regions

Excessive kyphosis

"hunched over" posture, aka swimmers' back

Excessive Lordosis

Weakened abdominals, low back pain

Scoliosis

Lateral deviation of the spinal column can be a "C" or "S" shape

Thoracic and Lumbar

What regions does Scoliosis involve?

SScoliosis

associated with disease, leg length abnormalities, muscular imbalances, and repeated unilateral loading

Forward Trunk Tilt

Trunk weight creates a forward bending torque, which must be counter-balanced by ligaments and muscles