`Why Use Seat Belts?Larry Brandon                  Thornwood High School                               17000 South Park Avenue                               South Holland IL 60473                               (708) 339-7800Objective:     To show some reasons for wearing seat belts.Materials:   Per Group:        Board (for ramp - length about .75 m to 1.0 m)        Dynamics cart        Books (for propping up one end of board + 1 for barrier)        Clamp (to fasten barrier down to table top)        Plasticene (or modeling clay)        Meter stick or ruler   For Teacher Demonstration:        Barbie doll or similar type doll        A seat and dash assemblyStrategies:Number 1: Teacher Activity     As a demonstration, put a Barbie doll on a block seat on a dynamics cart. Place the cart at the top of a ramp which is set with the top 30 cm above the table top.  Clamp a book down as a barricade about 50 cm from the bottom of the ramp.  Release the cart and observe where the doll ends up after hitting the barricade. Number 2: Student Activity     Mark the ramp into 20 cm intervals.  Raise one end of the ramp about 30 cm. Position an obstacle such as a book about 30 cm from the bottom of the ramp. Hold the obstacle stationary.      Make a plasticene (modeling clay) cube "passenger" with sides about 2 cm long.  Place the passenger on the front of a dynamics cart.  Place the front of the dynamics cart at the 20 cm mark on the ramp.  (It may make results more graphic if students shape the plasticene into a roughly human shape.)      Release the cart.  Observe the motion of the passenger during and after the collision.  Measure the distance the passenger moves from the collision point to where it stops.  Repeat this step several times and average the distance.      Release the cart from several different distances up the incline to vary the speed.  Observe the motion of the passenger and measure the distance as in the previous paragraph.  Repeat this procedure several times for each measured 20 cm mark to average the distances. Possible Extensions:        By spending some money at your local Venture or similar store, you can obtain some "Crash Dummies" and a "Crash Dummy Car."  They claim to have a "Crash Dummy Cycle" as well.  The car has a facility built in for attaching seat belts.  It also gives a very satisfactory crash in that the roof and windshield and front wheels go flying off.  If the dummies hit hard enough, they may also fly apart.  Students should also get a thrill from this.         Another extension would be to use ticker tape timers and attach ticker tape to each dummy as well as the car.  This would provide a difference in time of movement as well as distance differences. Performance Assessment:     (The following questions should be made available.  If students have trouble with the questions, the equipment should still be available.  They should obtain their equipment again and do what is needed in order to answer the questions.)  1.  Describe the motion of the passenger during and after the front-end      collision.  2.  How did the speed just before the collision change as the cart was released      from further up the ramp? 3.  How did the distance the passenger rolled after the collision change as the      cart was released from further up the ramp? 4.  Describe the motion of an unbelted passenger in a car which collides with a      stationary obstacle. 5.  Draw a diagram of the forces acting on the cart and on the passenger on the      flat before and during collision. 6.  Seatbelts prevent a passenger from being thrown from the car.  Why is it      usually more dangerous to be thrown from the car than to remain in it? 7.  Newton's First Law says (in essence), it takes an unbalanced force to      change velocity.  Explain how this applies to the motion of the passenger      during the collision.Multi-Cultural Implications:     The implications of this laboratory experiment tend to be related to age rather than culture.  My observation tends to the idea that mature individuals use seatbelts more than teenagers do.  However, European countries do not have speed limits on their highways.  Therefore, the Europeans do wear seat belts more than Americans do! `