Center of Gravity/ Equilibrium?

Question

1) When a person carries a heavy mass, such as a pail of watere, the center of gravity of the loaded person shifts towards the mass. What actions are taken by the person to maintain stability?

2) Why is it easier to pick up a long pole at its centre of gravity than to lift it horizontally from one end?

3) Why do high heels increase the chance of ankle injury?

4) Empty ships returning to port are usually loaded with ballast. In the past, rocks were used, but water is usually used nowadays. Why is ballast added?

Answer 1

1) they have to lean over a bit so the c of g is above their feet.

if it wasn't, they would topple over.

This suggests the answer to (3)

2) so the c of g of you holding  the pole is thru your hand , iotherwsie you would be pulled over.

4) to get the c of g below the waterline so the boat doesn't roll

Answer 2

1. He tries to lean over to the other side of the load to bring the center of gravity of their combined masses within the line of his body so he won't tip over on the side of the mass he is carrying.

2. Aside from exerting a force equal to the weight of the pole you will still have to counteract the moment created by the weight of the pole and the distance of its center of gravity to your hand if you pick it up at the end.

3. The high heels will raise your center of gravity from the ground and it would be more difficult a little for you to maintain your balance.

4. Contrary to the common notion that water ballast are used to lower the center of gravity of an empty ship, the liquid ballasts are primarily for the purpose of sinking the vessel to a favorable draft so that the propeller can function efficiently and to have a favorable trim during the voyage back. Ships are normally designed such that they have the necessary stability even at lightship condition. Of course the liquid ballast would bring down the center of gravity of the vessel as most ballast tank are located at the lower compartments of the vessel, but loading liquid ballast does not always improve the stability of the vessel. If ballast tanks are not loaded properly. the resulting free surface effect may be more than the effect in the reduction of the distance of the center of gravity from the keel. I should know. I've been doing stability calculations of vessels for the past 45 years.