Which is not in dynamic equilibrium?

Question

Which is not in dynamic equilibrium? Plz explain why..

a.) a child riding a bicycle
b.) water and stream in a closed container
c.) water dripping from a faucet
d.) water and salt sol'n separated by a semipermeable membrane

Plz explain why...tnx..

Which is not in dynamic equilibrium? Plz explain why..

a.) a child riding a bicycle
b.) water and stream in a closed container
c.) water dripping from a faucet
d.) water and salt sol'n separated by a semipermeable membrane

Plz explain why...tnx..

I nid a simple explanation because I will use the answers in my report..I nid an explanation that high school students can understand...

Answer 1

The definition of equilibrium is that which is characteristically unchanging, even though the system may be in motion. So,

a) A child riding a bicycle can do so practically indefinitely, so it's in DE, or at least until the child runs out of food and energy.

b) Water and STREAM in a closet container cannot last, because by definition a stream is falling water, which must be replenished, which is impossible in a closed container, which assumes no transfer of matter or energy. So, this cannot be in DE

c) Water dripping from a faucet can do so practically indefinitely, so it's in DE

d) Water and salt solutions separated by a semipermeable membrane in theory can reach a state of different salinity for indefinite time, so it's in DE

Addendum: Actually, I liked Zor Prime's answer, since he has looked at this question from a different angle, and I agree with him. The problem is that this is a badly posed question, and I have no idea at all what class this is for. It does not sound like a question being posed in a physics class studying dynamics, so my answer was based on guessing that this is a high school question.

Answer 2

Lancenigo di Villorba (TV), Italy

THESE BELONG NOT TO CHEMISTRY QUESTIONS.

I AGREE NOT PREVIOUS ANSWER.

DYNAMIC EQUILIBRIUM involves two "Cardinal equation of motions", e.g. the followings :
First One) differential of "System's Momentum" results by vectorial sum of forces acting on the system;
Second One) differential of "System's Angolar Momentum" results by vectorial sum of force's momenta acting on the system.
WHEN THE OVERWRITTEN DIFFERENTIAL ARE EQUAL TO ZERO, YOU FIND DYNAMIC EQUILIBRIUM.
Applying the differential realtion in the cases, I found the ANSWER is LETTER C).

A) Child push ahead his bicycle while the wheels turn respecting the Cardinals equations. If the system (e.g. wheels, bicycle and child) accelerates not, there is DE.

B) In a closed system, water is underlying steam in a vapour phase. There is not any motions, there is DE.

C) A cylinder filled by water dripps off a small flow of the liquid by a faucet. This is a common example showing the "Third Principle of Dynamics", in effects the system move away since there is not DE.

D) By means of a semipermeable membrane, water flows from the deionized solvent toward the brine solution. This process involves DIFFUSIVE EVENTS, it interests not any motions. There is DE.

I hope this helps you.