questions

[wasizaamm43]

think a body which is at rest but not in equilibrium?

[swansont]

This sounds like homework (moved to HW help) and we’re not going to do it for you.

What have you done thus far?

[Country Boy]

What does "at rest" mean?  What does "equilibrium" mean?

[Country Boy]

Suppose an object is moving along a straight line with position given by x= t^2- 8t where x is the directed distance in meters from some fixed point and t is the time in seconds.  At t= 4 seconds its speed is 0.  Is it "at rest"?  Is it "in equilibrium"?

[Country Boy]

I am wondering if you are not confusing "equilibrium" with "stable equlibrium".

First imagine a ball rolling up a hill.  If it does not have enough kinetic energy to get to the top of the hill, it will slow to a stop, then roll back down the hill.  At the instant it stops, it is momentarily "at rest" but it is not "at equilibrium" because there is a net downward force.

Second imagine a ball sitting in a valley between two hills.  There is no net force because the downward force of gravity is offset by the upward force of the ground on the ball.  The ball is "at rest" and "at equilibrium".  If it were disturbed slightly, so that it moved a bit, it would roll back to the bottom.  That is a "stable equilibrium".

Finally imagine a ball sitting at the top of a smooth hill.  Again the only forces on the ball are gravity downward and the ground upward so there is no net force so the ball is "at rest" and "at equilibrium".  If it were disturbed slightly, so that it moved a bit, it would roll to the bottom of the hill.  That is an "unstable equilibrium".

[studiot]

21 minutes ago, Country Boy said:

I am wondering if you are not confusing "equilibrium" with "stable equlibrium".

First imagine a ball rolling up a hill.  If it does not have enough kinetic energy to get to the top of the hill, it will slow to a stop, then roll back down the hill.  At the instant it stops, it is momentarily "at rest" but it is not "at equilibrium" because there is a net downward force.

Second imagine a ball sitting in a valley between two hills.  There is no net force because the downward force of gravity is offset by the upward force of the ground on the ball.  The ball is "at rest" and "at equilibrium".  If it were disturbed slightly, so that it moved a bit, it would roll back to the bottom.  That is a "stable equilibrium".

Finally imagine a ball sitting at the top of a smooth hill.  Again the only forces on the ball are gravity downward and the ground upward so there is no net force so the ball is "at rest" and "at equilibrium".  If it were disturbed slightly, so that it moved a bit, it would roll to the bottom of the hill.  That is an "unstable equilibrium".

I think you are kicking a dead donkey.

Though you are working very hard,

The OP hasn't been back since the day he joined and posted.

[Country Boy]

Have you ever kicked a live donkey?

[Phi for All]

1 hour ago, Country Boy said:

Have you ever kicked a live donkey?

The donkey will kick you back, and that's what we call "stable" equilibrium.

[Sensei]

5 hours ago, Phi for All said:

The donkey will kick you back, and that's what we call "stable" equilibrium.

I thought so it was Newton's 3rd law action-reaction.. but what I know..

[Country Boy]

18 hours ago, Phi for All said:

The donkey will kick you back, and that's what we call "stable" equilibrium.

And that's why I kick dead donkeys!

[Phi for All]

13 hours ago, Sensei said:

I thought so it was Newton's 3rd law action-reaction.. but what I know..

Newton kept his donkeys in the house because their knowledge of the law was unstable. 

[swansont]

I hope you're just yoking about this.

[Phi for All]

It's no yoke when one of the donkeys dies. The other one just moves in a circle, and because of Newton's 1st Law, it might just burro right into the ground.

[swansont]

Does it matter if these are males of females? Typically the female is wearing ze bra.

[Phi for All]

It matters if you're speaking onager mane topic.

[exchemist]

It seems to me a lot of this is old gnus.