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Inertia of a car wreck demonstration        


  • lab cart
  • 2 x 4 x 4 (seat)
  • 6 to 8 inches of 4 x 1/2 (back)              
  • 3 threaded cup hooks
  • ken doll                        
  • two rubber bands
  • string   
  • weight
  • table clamp pulley
  • 2 wood screws 3/4 inch
  • 2 wood screws 2 1/2 inch


  1. Screw back to seat using two wood screws.
  2. Screw threaded cup hooks into back.  One should be just above the shoulder height of the doll when seated and the other two at waist level.  These are the anchor points for the seat and shoulder harness.
  3. Fasten seat assembly to cart.  Use wood screws(for permanent) or duct tape to attach the seat to the cart.  If using screws through the cart, drill pilot holes.
  4. Tie the string to front of cart and the other end to a kilogram or so mass.  Place table clamp on end of table and position crash wall in place. The crash wall is two 2 x 4 x 4 sections c-clamped to the table with a 12 x 4 x 4 laying up against them. This prevents the collision damaging the table top pulley.


Use the two rubber bands as lap and shoulder belts.  Ken can crash wearing no restraint, lap only, shoulder only, or both.  Students can easily see the types of injuries that may occur when not secured properly.  I find the students are interested in the evolution of automobile safety features.  When conducting the demonstrations move the students away from describing ken as being “thrown from the car” and towards correct statements involving inertia and forces exerted on the car. My Ken is nicely “seasoned” and his head pops off most dramatically when wearing only a shoulder harness.

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