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Concepts

Projectile motion

Overview

A monkey (held by an electromagnet) in a "tree" will fall when startled by blowgun fire (which breaks a wire to cut off the electromagnet current). The question for students is this: where should the gun be pointed to strike the monkey? Should it be aimed above, below, or straight at the monkey? Answer: straight at the monkey.

Details

Equipment

• [1] Mounted blowgun
• [1] Vacuum with hose and adaptor
• [2] Hose clamp
  
• [1] Bullet
• [1] Mounted electromagnet
  
• [1] Mounting pole
• [1] Pole clamp
• [2] Wooden block
  
• [1] Current supply
• [2] Banana cable
• [1] Spool of thin wire
• [1] Strip of aluminum foil
  
• [1] Monkey with Velcro strap and aluminum plate
  
• [1] Can
  
• [1] Lifter poles for monkey and can
• [1] Foam
• [1] Extension cord
• [1] Power bar
  
• [1] Long double banana cable
  
• [1] Stick
• [1] Ethanol bottle
• [1] Box of wipes
• [1] Metal cart

Classroom Assembly

1. If blowing the bullet, sanitize the blowpipe with ethanol and a wipe.
2. Mount the electromagnet on the cart using the mounting pole, clamp, and wooden blocks.
   
3. Connect the electromagnet to the blowpipe with strain-relieved cables.
4. Set switch to "on" position.
   
5. Connect wire or aluminum foil across the blowpipe exit.
   
6. Plug in and set the current supply to the appropriate output (monkey: 0.5 A; can: 1.5 A).
7. Set switch to "off" position.
8. Lay down the foam under the electromagnet.
9. If using the monkey, attach the plate to the monkey.
   
10. Test magnet's ability to hold monkey/can.
11. Turn off the current.
    
12. Check the aim of the blowpipe.
13. If using the vacuum to blow the pipe, use the hose clamps to hold the hose to the vacuum and the adaptor.
    
14. Lock the wheels on the cart.
    

Important Notes

• Practicing this demo before class is highly recommended.
• Make sure no one is in the line of fire should the bullet miss or riccochet.
  
• Remember to turn off current to the electromagnet when not in use. The magnet can get very hot.
• Moderately good breathing strength is required to operate the blowgun, though a vacuum is now available to fire the bullet.
  
• The bullets are very easy to lose. Please try to recover them after firing.
  
• When attaching the thin wire to the blowpipe, make sure to loop the wire around the holder at least once on each side.
• The stick is to push a bullet out of the tube in case it gets stuck.

Script

1. Tap the bullet on the monkey's armour plate, noting the sound.
   
2. Double-check the aim of the blowpipe.
3. Insert the bullet.
4. Turn on the current.
   
5. Take a deep breath and blow out the bullet, or place the adaptor side of the hose over the blowpipe and turn on the vacuum.
   
6. Turn off the current and vacuum, if applicable.
7. Find the bullet.

Additional Resources