Bed of Nails, 1K30.10

Location:

• Floor Item [:MechanicsCabinet:Mechanic (ME)]

(attachment photo showing the fully set up demonstration)

Description:

A 2′ by 4.5′ bed of nails is made up of 80d nails placed in a 1" grid. The bed contains 1375 aluminum nails which have been leveled and dulled. A second bed of nails (1.5′ x 2.5′) made up of 425 aluminum nails placed in a 1" grid can be placed on top of the person lying on the larger bed of nails. For extra excitement, break a cinder block that is placed, centered and stable, on top of the small bed of nails.

Important Setup Notes:

1. This demonstration requires three people: One brave volunteer and two people to assist the volunteer onto and off of the bed.

2. The large bed is awkward and heavy.

3. Have the volunteer removes glasses and/or jewelry and PA transmitter too, if wearing one.

Setup and Procedure:

1. Place larger bed of nails onto level floor. Place the bed on two cinder blocks for extra height and or comfort.
2. Have volunteer stand with back to bed, feet about 6" from base
3. Have two people, one on either side of the volunteer, grab the arms of the volunteer and slowly lower volunteer onto bed
4. After volunteer is laying on bed, place the pillow beneath his or her head

When Breaking a block:

1. Put face shield on volunteer
2. Gently place smaller bed of nails nail-side-down on top of the volunteer so that it is stable, centered on the volunteer's torso
3. Place a board, leaning with its bottom on the volunteer's lap leaning onto small bed so that ones groin is covered from falling debris.
4. Place cinder block vertically-oriented in a stable position, centered on the back of the smaller bed of nails
5. With a lite overarm stroke, use sledge hammer to smash cinder block, while wearing safety glasses.
6. Remove any debris from the bed and the volunteer
7. Gently remove small bed from volunteer's torso
8. Have two people, one on either side of the volunteer, grab an arm and gently assist the volunteer off the bed of nails

Cautions, Warnings, or Safety Concerns:

1. Even though the nails have been blunted, they are still extremely sharp and can cut skin which my cause bleeding.

2. Be careful not drag the volunteer along the nail bed when placing the volunteer onto the bed of nails. This could scratch/cut the volunteer or tear his or her clothing!
3. Demonstration may require practice.
4. Be sure to get permission from the volunteer to perform each stage of the demo
5. Be sure proper face shield and eye protection are worn.
6. When smashing the block, make sure to hit the block with a sold hit..."Do not miss the block" for this could cause great harm to the volunteer.

Demonstration:

Several physics principles are involved here, Presser, Force, Inertia.

The total force on the bed of nails is spread out among all the nails that are in contact with the Volunteer. Thus each nail only takes a faction of the total weight of the volunteer plus the cinder bock. In fact with our setup, one can stand on the top of the small bed of nails instead of having a brick. The total force is still spread out among the nails and the force back from "any one" nail is greatly reduced. For an example, take an average human of 175 pounds. Our lower bed has 1375 nail, however not all are in contact with the person so lets say that 60% are. Then the weight is spread out among approximately 825 nails, therefor you'll only feel about 0.21 pounds(~3.4 ounces or ~95 grams) of force per nail - on average. Some nails will bit more and some will bit less. With a person standing on top, the force per nail is roughly doubled, to 0.41 pounds of force per nail, for both beds. Slightly unconformable but not close to the threshold of pain which is approximately 2 pounds of pressure.

The upper bed only has 425 nails and are, for the most part, all in contact with the volunteer's torso. The smashing of the block its self absorbs much of the energy of the sledge hammer blow. The block's inertia protects the person from the force of impact. When the sledge hammer smashes the block, the volunteer will experience an additional force. However, the cinder block is so massive (~37 pounds) that almost all of the impulse will be absorbed by the block upon impact.

Videos

• [http://youtu.be/mQZIkO1f7Xg Bed of Nails, 1K30.10]

• [https://www.youtube.com/user/LectureDemostrations/videos?view=1 Lecture Demonstration's Youtube Channel]

References:

1. N/A

[:Instructional:Home]