Is momentum conserved for SHM?

[mytoechondriac]

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I know momentum is conserved whenever you have no external forces acting on the system-- so for simple harmonic motion, like a pendulum or Hooke's Spring Law, is momentum conserved? I am confused about this because momentum is a vector and I recall reading in an AAMC solution manual that during a pendulum or Hooke's spring, momentum is NOT conserved because it is a vector quantity. But I know that the TOTAL energy is conserved in SHM if you ignore heat and friction. And I don't know if the act of releasing the spring or releasing the pendulum is considered an "external force." Can someone tell me if I'm right or wrong?

THANKS!!

 

[engineeredout]

AFAIK its not necesserly momentum that is conserved but energy. Momentum is mass times velocity. The velocity is constantly changing.

And releasing the spring/pendulum is not an "external force", because it is analgous to dropping a ball off a cliff. Just dropping it is not giving it a force.

 

[mytoechondriac]

Once again, THANK YOU engineered!!

AFAIK its not necesserly momentum that is conserved but energy. Momentum is mass times velocity. The velocity is constantly changing.

And releasing the spring/pendulum is not an "external force", because it is analgous to dropping a ball off a cliff. Just dropping it is not giving it a force.

 

[engineeredout]

Just to add though, ENERGY would be conserved in a pendulum collision, like with these:

 

[ballofnerves]

Yes, momentum is always conserved in collisions. Since there is no collision occurring with a simple pendulum or a mass on a spring, there is no need for momentum to be convserved.

Just another way to think about it.🙂

 

[Kaustikos]

Just to add though, momentum would be conserved in a pendulum collision, like with these:

I'm curious; you say momentum is conserved here, but this still uses the same velocity change of a normal pendulum. How is momentum conserved?

 

[engineeredout]

I'm curious; you say momentum is conserved here, but this still uses the same velocity change of a normal pendulum. How is momentum conserved?

GAHHH I ment energy!! Good catch.

 

[tco]

Actually momentum is still conserved.

There is a collision with Newton's Balls.

This means momentum is conserved.

 

[engineeredout]

Wait what **** I've gone and confused the **** out of myself now. You're all screwing with my mind. I hear your voices in my head. Don't think I don't notice they're there, because I do notice, and I don't like it. You're all conspiring against me. You all want me to loose my mind so come mcat day my perfect 45 won't throw off your curve.

 

[tco]

K.

 

[Isis24]

Gravity would be an external force. you can't consider momentum to be conserved when a ball is being dropped or if you're observing projectile motion. In both of those cases, the velocity changes (the ball is accelerating at 9.8 m/s/s, right?). if the velocity changes and the mass is the same (which it clearly is), then momentum is NOT conserved. p=mv.

 

[Isis24]

Also...momentum is only discussed when two or more objects collide. And they usually collide horizontally, so we don't really consider gravity.

 

[Heyeon]

Yes, momentum is always conserved in collisions. Since there is no collision occurring with a simple pendulum or a mass on a spring, there is no need for momentum to be convserved.

Just another way to think about it.🙂

Good Point! 🙂

 

[AZFutureDoc]

You release the object, it has zero momentum initially. Now potential energy is converted to kinetic energy. the kinetic energy is all used up to get the object to the displacement point that is against gravity.

After one complete cycle, it seems that momentum should be conserved. You let the object go, it eventually comes back to the exact same spot.