1K30.10-Bed of nails

Video: Precursor video

Another precursor with a larger area

Instructor’s video

Description: An impressive demonstration to show that pressure is force per unit area.
When maximizing the area (lying on the bed of nails), the force at each point of contact (each nail) is minimized.

Equipment:

• Long table
• Bed of nails
• Two c-clamps
• Stepping stool
• Balloons
• A book

Setup Procedure:
Note: When moving the bed of nails, carry it with the nails facing AWAY from you.
If you are carrying it by yourself, make sure to hold it at the center of mass, and hold the top AND bottom, so it doesn’t tip over.

1. Place the bed of nails on a long table, or on the floor.
2. If the bed of nails is on a table, CLAMP the bed of nails to the table, so that it can’t slide around.
3. MAKE SURE to place a book on the head of the bed of nails. You don’t want anyone’s head to get punctured!
4. Have a stepping stool next to the table (if using a table).

Demonstration Procedure:

1. Place your feet on either side of the bed of nails.
2. Gently lower yourself down to a sitting position on the bed of nails. (NOTE: DO NOT place your HANDS on the nails. The area of your hand is small enough that if you put much weight on it, you will get punctured!)
3. Lie down on the bed of nails, with your head on the book.
4. At this point you may want to also do the “Breaking a cinder block on the bed of nails” demo (LINK).
5. To get off the bed of nails, first sit up. Then stand, being careful not to put your hands on the nails.

Note: For safety, place something hard (such as an old book) where the head will rest.
The bed of nails is very heavy. Never carry it with the nails facing you.
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