Falling Chimney: Difference between revisions

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== Age ==
{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Physics]]:
| Moment of Inertia
|-
| Grade Range:
| [[Elementary School]], [[Middle School]]
|-
| Format:
| [[Hands-on]]
|}


Elementary School, Middle School, High School
This demonstration is easy to explain, and students enjoy seeing the ball land in the cup over and over again. Easy to setup and easy to present, this is a good demonstration for science fairs.
 
== Format ==
 
Stage Show, Hands-on


== Materials ==
== Materials ==


    "Chimney" (Board with cup and hole for the ball)
* Hinged Boards with Attached Cup
    Ball
* Prop Stick
    Stick to hold up the chimney until you are ready to let it fall
* Small Plastic Ball
* Golf Tee


== Safety Precautions ==
== Safety Precautions ==


Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.
Please read the Physical Demonstration section of the [[Demonstration Safety]] page before performing this demonstration.
 
No real safety gear is needed for this demo. Just make sure that ALL hands are away from the chimney when it falls. Also be sure that nobody accidentally knocks the chimney down before you are ready to let it happen.
 
== Preparation ==
 
Once you have the materials, there is very little preparation. Set the stick under the chimney so that it won't fall, and add the ball to the top of the chimney.


== Demonstration ==
== Demonstration ==


Once you have prepared, the demonstration is as easy as pulling out the stick and watching the chimney fall. If everything goes well, the ball will end up in the cup.
# Set up the demonstration: stick the tee into the front of the cup board, and prop up the board with the prop stick. There will be a small notch in the back of the board for the stick to sit in. balance the plastic ball on the tee.
 
# When students come up, ask them if they think the ball will land in the cup when you pull the prop stick away. Proceed with the demonstration, and see that the ball does land in the cup!
== What to Say ==
 
Has anyone ever seen a chimney fall? (Very unlikely, but if someone has, ask if the chimney broke in 2 as it was falling)
 
Well an interesting thing about a chimney falling is that the top of the chimney will actually end up falling faster than if it were just in free fall.
 
So if I put a ball at the very top of the chimney and let it fall in free fall, it would fall slower than the very top of the chimney.
 
When I take the stick out, the chimney will hit the ground first, with the cup ending up underneath the ball and then the ball will fall into the cup. It all happens very fast, so watch closely.
 
(Count down to the release of the stick so that everything can fall into place)
 
So this is why sometimes if you see a chimney fall, it will break into 2 pieces. The top part is trying to fall faster than it would in free fall, and it puts a lot of stress on the chimney. This causes the chimney to break, making the top part fall slower than it was previously.
 
== Why It Is ==


Some simple kinematics can explain this one. Say that instead of a chimney, we have two balls that are allowed to drop in free fall. They are both held in place along an imaginary straight line from the origin at 45 degrees (this is where the chimney would be). One ball is held 0.5 meters from the origin along the line and the second ball is held 1 meter from the origin along the line. If we were to let both balls fall at the same time, they would have the same linear velocity. If we examine the angular velocities of the 2 balls though, where ω = v/r, we see that it is inversely dependent upon the radius. So the ball that is closer to the origin has an angular velocity that is twice as much as that of the ball at 1m.
== Why This Works ==


Now, if we turn this imaginary line into a real line (the chimney) and let it fall from 45 degrees, since it is a rigid line all points on it must have the same angular velocity. So in effect, the points lower down on the chimney are "making" the top part of the chimney fall faster than it would have if in free fall.
When we pull the stick out, we see that the ball lands inside of the cup. This is due to ''Inertia'': An object in motion stays in motion, and an object at rest stays at rest. The board and the ball start to fall the moment the stick is pulled. The ball is not affixed to the board, so it will fall straight down, and be unaffected by anything but gravity. The board, however, is falling at an angle due to the hinge. This means that the board is affected by gravity, but it is also experiencing a change in ''angular velocity''. This means that, since the board starts out falling sideways and downwards, that it will fall downwards ''faster'' as it loses sideways movement. This allows the board to land before the ball, and the ball to land in the cup!


== Real Life Examples ==
== Additional Information ==


A chimney in Glasgow falling. As you can see, after the break, the lower part of the chimney is at a steeper angle than the higher part. This is because the angular velocity of the lower part is faster than the higher part.
* This demonstration pairs well with the [[Where's the Doorknob]] and the [[Uphill Roller]] demonstrations

Latest revision as of 20:17, 23 May 2016

Physics: Moment of Inertia
Grade Range: Elementary School, Middle School
Format: Hands-on

This demonstration is easy to explain, and students enjoy seeing the ball land in the cup over and over again. Easy to setup and easy to present, this is a good demonstration for science fairs.

Materials

  • Hinged Boards with Attached Cup
  • Prop Stick
  • Small Plastic Ball
  • Golf Tee

Safety Precautions

Please read the Physical Demonstration section of the Demonstration Safety page before performing this demonstration.

Demonstration

  1. Set up the demonstration: stick the tee into the front of the cup board, and prop up the board with the prop stick. There will be a small notch in the back of the board for the stick to sit in. balance the plastic ball on the tee.
  2. When students come up, ask them if they think the ball will land in the cup when you pull the prop stick away. Proceed with the demonstration, and see that the ball does land in the cup!

Why This Works

When we pull the stick out, we see that the ball lands inside of the cup. This is due to Inertia: An object in motion stays in motion, and an object at rest stays at rest. The board and the ball start to fall the moment the stick is pulled. The ball is not affixed to the board, so it will fall straight down, and be unaffected by anything but gravity. The board, however, is falling at an angle due to the hinge. This means that the board is affected by gravity, but it is also experiencing a change in angular velocity. This means that, since the board starts out falling sideways and downwards, that it will fall downwards faster as it loses sideways movement. This allows the board to land before the ball, and the ball to land in the cup!

Additional Information

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