Bed Of Nails: Difference between revisions

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


Elementary School,Middle School,High School
This demonstration is a big and flashy way to show how pressure works. Be sure to not let anyone in the audience to lie on the bed of nails, '''''especially not children'''''! The bed and blanket of nails are very much real, so be safe while handling and using this demonstration.
 
== Format ==
 
Stage Show


== Materials ==
== Materials ==


    Two blast shields
* Blast shield
    Equipment in black box
* Bed and blanket of nails
 
* Yellow wooden rear and head supports
    Bed and blanket of nails
* Two black wood boards
    Yellow wooden foot and back supports
* Thick gloves
    Black wood leg coverings (x2)
* Sweatshirt
    Thick gloves for sleeper (x2)
* Sledgehammer
    Goggles for sleeper
* Metal cinder block holders (x2)
    Sweatshirt for sleeper
* Dixie Cups
    Sledgehammer
* Plastic tarp
    Metal cinder block holders (x2)
* Cinder block
    At least 36 paper cups + 1 extra per performance
* Black bin
 
    Plastic tarp
    One cinder block for each performance
    One backup cinder block per 3 performances


== 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. Safety is extremely important for this demonstration. If you have an audience member stand on the paper cups, hold their hand to steady their balance and instruct them to step on and off slowly. Ensure proper body support for participant in bed. Between the box, the wooden coverings, the gloves, and the goggles; the sleeper's entire body should be covered before the cinder block is put down. Keep crowd at a safe distance and behind blast shields. Make sure to tell people not to try this at home! Never invite an audience member to lie on the bed of nails.
Please read the Physical Demonstration and Flying Particles sections of the [[Demonstration Safety]] Page before using this demonstration.


== Preparation ==
This demonstration requires: Goggles or Safety Glasses, Blast Shields


Make sure the presenter who will be using the sledgehammer has practiced breaking the cinder block so they know how much force to use. Use as little as possible for the safety of the sleeper! Set up the blast shields between where the bed of nails will be and the audience, although you may choose to keep the bed of nails hidden at first for effect. Lay down the tarp behind the blastshield, where you will put the bed.


== Demonstration ==
== Demonstration ==
Preparation: Set out ''at least'' 30 paper cups in a square, and place one of the black wood boards on top of the cups. Both presenters during this performance must wear goggles or safety glasses the entire time.


For young audiences, you may want to introduce the bed of nails with a simple demonstration of pressure. Have an audience member step on one paper cup to demonstrate applying a force to a small surface area. Next, setup an array of at least 36 paper cups and place one of the black wooden leg covers on top of them. Invite another audience member to slowly and carefully step onto the board and stand there. Make sure they step onto the middle of the board, not an edge. The larger surface area of the array of paper cups should sustain their weight.
# Ask for two volunteers, and try to get one young student and either a second, older student, or a teacher. Have the young student try to stand on a single cup without breaking it. Inevitably, it will break. Now have the older student or teacher stand on the wood board on top of the paper cups, making sure to step into the center. The cups will hold them up!
 
# Explain to the audience why the cups could hold up the volunteer, and let the volunteers return to their seat. Have a co-presenter pick up the bed of nails and show it to the audience, and state that you will be lying on it.
Next prepare the bed of nails. First get out the bed itself (the bed is the one without the extra wood edge on the base, which are handles) and show it to the audience. Lay the bed of nails down on the tarp. Set up the yellow wooden headrest and footrest.
# Set up the Bed: Put the bed of nails on top of the tarp, and place the support boards down on either side of the bed. Although not required, it is recommended that you put on the Science Theatre sweater before lying on the bed, so to make it more comfortable. Have your co-presenter give you the gloves to wear. ''Make sure you are wearing goggles or safety glasses!'' Then, your co-presenter places the blanket of nails on top of you.
 
# Have your co-presenter place the wooden boards across your legs, then the bucket over your head, with the edge on the blanket of nails. Then, have them place the blast shield(s) in front of the bed of nails, between the demonstration and the audience.
Before lying down, the sleeper should take the following safety precautions. They may seem like more than is necessary, but safety is extremely important for this demonstration. Note also that the sleeper is usually a male, for anatomical reasons.
# Co-Presenter: Show the audience the cinder block. place the metal bars on top of the blanket of nails, and rest to cinder block across the bars, making sure the bars are not underneath the holes in the cinder block. Then, show the audience the sledgehammer, and state that you will be smashing that cinder block with the sledge hammer. Have the audience give you a countdown, and at the end of the countdown swing the sledgehammer down onto the cinder block.
 
## You do not need to hit the block hard; letting the hammer drop from a close to vertical point will give it enough energy to break the cinder block. Make sure it hits the cinder block either between the two bars or on either side of them, otherwise it might not break, and you will have to do a second swing.
* Wear goggles
# After the cinder block is broken, clear any debris off of the blanket of nails and help the presenter get up. Have the presenter show the audience that they are uninjured by spinning slowly to show no holes or injuries. They can now remove the sweater if it was worn.
* Wear thick gloves
* Wear sweatshirt
 
When the sleeper is ready to lie down, follow this procedure (and see diagrams below):
 
* Have the sleeper slowly lie down on the bed of nails, place head in headrest, and place feet in footrest.
* Another demonstrator should then slowly hand the sleeper the blank of nails and the sleeper should lower it onto his/her chest and hold it securely by its handles (the extra wood at the edge of the base).
* The other demonstrator should place the two black wooden pieces to cover the sleeper's legs.
* The other demonstrator should use the large black box to cover the sleeper's head and neck.
* The two metal rods should be placed in the center on top of the blanket of nails and the cinder block placed on top of it. Don't leave the cinder block on the sleeper's chest for too long - it's heavy!
* Have the audience count down for you and then break the brick with the sledgehammer. This doesn't take all that much force - make sure you have practiced beforehand! This is helpful so that the sleeper is aware of the timing of the hit.  
 
== What to Say ==
 
If performing the portion of the demonstration with paper cups, you can start out by asking if they would rather be stepped on by an elephant or a woman wearing high heels. Of course, the elephant applies much more force, but the area of his foot is far larger than the area of the high heel - the elephant would hurt less. Now ask why a volunteer can crush one cup, but not many. Once they start to get the right idea, point out that pressure, the phenomenon that causes a cup to crush or your body to feel pain, depends on both force and area. For young audiences, repeat this concept several times throughout the demonstration.
 
The bed of nails portion of the demonstration can be performed with a little humor, for young audiences. It might go something like this:
 
    Sleeper: ...yawn...
    Performer: Are you tired?
    Sleeper: Yes, we've done so many demonstrations today. I'm ready to go to bed.
    Performer: Well, you're very lucky, because I've brought a bed with me... put on your pajamas (sweatshirt)... here it is, a bed of nails!
    Sleeper: A bed of nails? I'm not going to sleep on that, it would hurt!
    Performer: No, it won't hurt at all! Back me up, guys, can you explain why it won't hurt?
 
Make sure the audience can explain the relationship between pressure and surface area
 
    Sleeper: Ok, I guess it doesn't sound that bad. Yah, it doesn't hurt at all! But I'm still cold.
    Performer: Well, you're even more lucky to have a friend like me, because I've also brought a blanket of 1000 nails! I know your hands are cold, too, so I've also brought these gloves. I even have a mask (black box) to shut out the light for you.  
 
After all the safety equipment is on, the sleeper can snore loudly
 
    Performer: Ok, he/she's asleep. Now we can try a little experiment. Since he/she's such a good friend of mine and because we're professionally trained scientists, I can try putting a cinder block on top of him. This cinder block is heavy and applies a lot of force, but you all know that it won't create very much pressure because of the large surface area of all the nails. Look, he's still sleeping! I can try applying even more force with a sledgehammer!


Now help the sleeper get off the bed.


    Performer: How was your nap?
==Why This Works==
    Sleeper: Great, but I had a strange dream that I was being stepped on by an elephant. Of course, it didn't hurt very much!


== Why It Is ==
When we had the single volunteer stand on a paper cup, it was crushed. This is because all of their weight is on the single cup, which is not able to support them. However, the other volunteer is able to stand on these cups, because their weight is spread out over all of them. This is the idea behind '''''Pressure''''': Pressure is when you take a force, such as someone's weight, and divide it over an area, such as these paper cups. If the area is big, then the amount of force is small on each cup, so they can support it. Likewise, if the area is small, then the force is high on each cup, so they are crushed.


Several physics principles are involved here. The force from any one nail is reduced by spreading the weight over many nails. The inertia of the blocks partially protects the person below from the force of impact. The smashing of the blocks absorbs much of the energy of the blow. If there were only one nail, the entire force created by the weight of the body would be distributed over the very small area presented by the tip of the one nail. In this case, the force per unit area, that is, the ratio of the force to the area, would be very great (because the area is small) and would likely result in piercing of the skin, and injury.
This works just as well with the Bed and Blanket of Nails. Each nail in the bed will take a small fraction of the person's weight, so each nail has a low amount of pressure on it. The amount of pressure on each of these nails doesn't increase much when we add the blanket of nails on top, or even with the cinder block! When we smash the cinder block, the force from smashing it is spread out over the nails, and results in a very small change in pressure for each, which keeps the presenter on the bed safe from harm. This would be very different if, instead of the several hundred nails we have here, it was only a couple dozen or even just one. By increasing the number of nails, and therefore the area to spread the force across, we decrease the amount of pressure on each nail.


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


Magic shows, feats of strength
* This demonstration is commonly performed with the presenter on the bed being the "Sleeper". After finishing the part with the paper cups, the "Sleeper" will act tired, and will then take a "nap" on the bed of nails. The other presenter will then wake them up by smashing the cinder block on top of them!
* This demonstration is a part of the [[Pressure Show]].

Revision as of 16:19, 30 September 2015

Physics: Pressure
Grade Range: Elementary School, Middle School, High School
Format: Stage

This demonstration is a big and flashy way to show how pressure works. Be sure to not let anyone in the audience to lie on the bed of nails, especially not children! The bed and blanket of nails are very much real, so be safe while handling and using this demonstration.

Materials

  • Blast shield
  • Bed and blanket of nails
  • Yellow wooden rear and head supports
  • Two black wood boards
  • Thick gloves
  • Sweatshirt
  • Sledgehammer
  • Metal cinder block holders (x2)
  • Dixie Cups
  • Plastic tarp
  • Cinder block
  • Black bin

Safety Precautions

Please read the Physical Demonstration and Flying Particles sections of the Demonstration Safety Page before using this demonstration.

This demonstration requires: Goggles or Safety Glasses, Blast Shields


Demonstration

Preparation: Set out at least 30 paper cups in a square, and place one of the black wood boards on top of the cups. Both presenters during this performance must wear goggles or safety glasses the entire time.

  1. Ask for two volunteers, and try to get one young student and either a second, older student, or a teacher. Have the young student try to stand on a single cup without breaking it. Inevitably, it will break. Now have the older student or teacher stand on the wood board on top of the paper cups, making sure to step into the center. The cups will hold them up!
  2. Explain to the audience why the cups could hold up the volunteer, and let the volunteers return to their seat. Have a co-presenter pick up the bed of nails and show it to the audience, and state that you will be lying on it.
  3. Set up the Bed: Put the bed of nails on top of the tarp, and place the support boards down on either side of the bed. Although not required, it is recommended that you put on the Science Theatre sweater before lying on the bed, so to make it more comfortable. Have your co-presenter give you the gloves to wear. Make sure you are wearing goggles or safety glasses! Then, your co-presenter places the blanket of nails on top of you.
  4. Have your co-presenter place the wooden boards across your legs, then the bucket over your head, with the edge on the blanket of nails. Then, have them place the blast shield(s) in front of the bed of nails, between the demonstration and the audience.
  5. Co-Presenter: Show the audience the cinder block. place the metal bars on top of the blanket of nails, and rest to cinder block across the bars, making sure the bars are not underneath the holes in the cinder block. Then, show the audience the sledgehammer, and state that you will be smashing that cinder block with the sledge hammer. Have the audience give you a countdown, and at the end of the countdown swing the sledgehammer down onto the cinder block.
    1. You do not need to hit the block hard; letting the hammer drop from a close to vertical point will give it enough energy to break the cinder block. Make sure it hits the cinder block either between the two bars or on either side of them, otherwise it might not break, and you will have to do a second swing.
  6. After the cinder block is broken, clear any debris off of the blanket of nails and help the presenter get up. Have the presenter show the audience that they are uninjured by spinning slowly to show no holes or injuries. They can now remove the sweater if it was worn.


Why This Works

When we had the single volunteer stand on a paper cup, it was crushed. This is because all of their weight is on the single cup, which is not able to support them. However, the other volunteer is able to stand on these cups, because their weight is spread out over all of them. This is the idea behind Pressure: Pressure is when you take a force, such as someone's weight, and divide it over an area, such as these paper cups. If the area is big, then the amount of force is small on each cup, so they can support it. Likewise, if the area is small, then the force is high on each cup, so they are crushed.

This works just as well with the Bed and Blanket of Nails. Each nail in the bed will take a small fraction of the person's weight, so each nail has a low amount of pressure on it. The amount of pressure on each of these nails doesn't increase much when we add the blanket of nails on top, or even with the cinder block! When we smash the cinder block, the force from smashing it is spread out over the nails, and results in a very small change in pressure for each, which keeps the presenter on the bed safe from harm. This would be very different if, instead of the several hundred nails we have here, it was only a couple dozen or even just one. By increasing the number of nails, and therefore the area to spread the force across, we decrease the amount of pressure on each nail.

Additional Information

  • This demonstration is commonly performed with the presenter on the bed being the "Sleeper". After finishing the part with the paper cups, the "Sleeper" will act tired, and will then take a "nap" on the bed of nails. The other presenter will then wake them up by smashing the cinder block on top of them!
  • This demonstration is a part of the Pressure Show.
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