How Do You Know if Linear Momentum Is Conserved

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Conservation of linear momentum and rotational motion

• Thread starter kavan
• Start date Dec 10, 2012

When you open a door you apply force in any detail direction and as a result you get rotational motion of the door. My question is how linear momentum is conserved in this case as linear momentum seems to accept generated rotational motion? To clarify my question farther, if we fix a rod from ane terminate such that it can freely rotate nigh that terminate then hit some other finish of the rod with a speeding ball with some linear momentum forth whatever direction(say x).. the momentum volition exist transferred to the rod which will outset to rotate...at present the rotating rod volition have linear momentum with components in both directions(say ten and y). How did the momentum along the y direction come into picture when originaly there was none?8

Final edited: Dec x, 2012

Answers and Replies

When you open a door you lot use force in any particular direction and as a result you become rotational move of the door. My question is how linear momentum is conserved in this example

Linear momentum is conserved in a airtight system equally long as there are no external forces on the system. In the case of a hinged door or rod in that location is an external forcefulness from the hinge.

How did the momentum along the y direction come into movie when originaly in that location was none?

The strength from the swivel has a component in the y direction.

Linear momentum is conserved in a closed organisation equally long as there are no external forces on the organization. In the instance of a hinged door or rod at that place is an external force from the hinge.

Nosotros can include the external strength within the organisation by suitably expanding it. Imagine collision case, a ball hitting the door makes 1 system on which there are no external strength.

The forcefulness from the hinge has a component in the y direction.

Didnt get that. If originally at that place were no momentum in y direction from where the momentum in y direction comes once the door starts rotating.

The hinge connects the door to... what exactly? If you lot are expand the system to include the wall the hinge is screwed into so y'all have to include the motion of the wall in your calculations.

Plz come across the screenshot attached. How did linear momentum of the brawl converted into athwart momentum of the rotating road. I hope I've clarified my question.

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  Screenshot_2012-12-23-19-07-39.png

How did linear momentum of the brawl converted into angular momentum of the rotating road.

Even before the collision, the ball has athwart momentum about the hinge. Angular momentum is conserved during the collision. (Linear momentum is not. Every bit already pointed out, you cannot ignore the strength of the swivel on the door.)

The swivel connects the door to... what exactly? If you are expand the organisation to include the wall the hinge is screwed into then you take to include the motion of the wall in your calculations.

And the wall is fastened to the edifice. And the building is fastened to the globe.

Linear momentum is conserved in the door, wall, building, world arrangement.

Now excuse me. I hear my Noether calling.

As for converting linear to angular momentum you take to know that everything that has linear momentum has athwart momentum too and the other way round.

When it comes to the standoff the free energy of the brawl is given to the door as momentum. The only motility that the door can perform is a rotation and therefore all of the energy goes in it. During the rotation the door's linear momentum is conserved inside the system door-hinge. The angular momentum is conserved for itself in the rotation.

When you summate information technology you volition run into that the angular momentum of the ball in relation to a random point is the same as the angular momentum of the door related to the aforementioned point.

The linear momentum of the rotating door cannot be described so well using Newtonian mechanics. Instead you demand the term of constraints since the hinge is a constraint for the door.

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Source: https://www.physicsforums.com/threads/conservation-of-linear-momentum-and-rotational-motion.658043/

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