Fettucini Physics |
Home Page of Peggy E. Schweiger
When my physics students see these images, they cannot believe that they are actually looking at a REAL bridge. Most students (and the majority of people) think that structures are strong and built to last. Students don't realize that a structure must be designed to withstand different forces. Some forces are obvious and then some are not so obvious. Everybody knows that if you build a bridge and a truck drives across it, the bridge needs to hold the weight of the truck. How many students realize that the bridge is also supporting its own weight?!
Structures need to be designed to withstand other forces, too, besides just the weight of the objects that they hold. Engineers need to consider lots of forces and how they effect the structure that they are designing. They have to design bridges and buildings that can withstand forces due to wind, earthquakes, etc.
In this activity, students will design and build a support structure that will hold their Physics textbook. After this has been successfully accomplished, students enjoy holding a contest to determine whose structure can hold the greatest number of Physics books without collapsing. Winners can be determined two ways. Load the structures according to the directions. In the event of a tie, the winner is the lightest of the structures. For your more advanced students, the winner could be determined by using an "efficiency" calculation (mass held divided by mass of structure).
Home Page of Peggy E. Schweiger
An object is in equilibrium when the net force acting on it is zero. Examine the forces acting. The weight of the object held is a force that acts downward. It is balanced by the normal force exerted on the object held by the structure. The normal force is a force that acts upward. As long as the weight (downward force) is balanced by the normal force (upward force), the net force acting on the object is zero and the object is in equilibrium. When an object is in equilibrium, there is no change in motion, so it is at rest (as in this case) or moves at constant velocity.
According to Newton's third law, the normal force exerted by the structure on the object is equal in magnitude, but opposite in direction, to the weight of the object. In other words, the normal force that the structure exerts on the object is equal to the weight of the object until the structure fails.
According to Newton's second law, a net force causes an object to accelerate. In this case, the sum of the normal force and the weight is zero represents the net force acting on the object. There is no acceleration and the object remains in equilibrium.
When the object falls, breaking the structure, the normal force exerted by the structure was insufficient to offset the weight of the object. The net force is no longer zero. The weight of the object is greater than the normal force. Now, the object accelerates downward (in the direction of the greater weight) until it strikes a surface whose normal force will balance the object's weight.
Students must be familiar with terms such as force, normal force, and weight.
Students must be familiar with Newton's three laws of motion.
Top of the page
Objectives
Top of the page
Item Held | |||
10 points |
20 points |
30 points |
40 points |
You don't associate a bridge with a dinosaur, but using physics to compare their structures explains much of the dinosaur's morphology.
In this part of the project, students will acquire information from Internet sources, enabling them to compare and contrast the structure of a bridge and that of a dinosaur.
How Do They Know That Dinosaurs Held Their Tails Erect?
Home Page of Peggy E. Schweiger
Here are some practice problems dealing with weight, mass, and Newton's second law (permission granted for inclusion of these problems by S. Sanders).
Permission granted for its inclusion by NOVA.
Why do different bridge designs work?
Practice quiz for Mrs. Schweiger's physics students.
These pages were developed through GirlTECH , a
teacher training and student technology council program sponsored by the Center for Research on Parallel
Computation (CRPC), a National Science
Foundation Science and
Technology Center. Copyright December 1997 by Cynthia Lanius.