20 Mar, 2012
With an egg
PRESENTATION: The throwing of an egg on a rigid surface produces the breaking of its shell, following Newton’s third law. If we allow the collision (interaction) time to be long enough we can reduce the interaction force so that it is not enough to break the shell, according to Newton’s second law.
- I “Saw” Newton’s Three Laws, Mike Shaw, Phys. Teach. 50, 480 (2012)
- Newton’s Apple, Archibald W. Hendry, Phys. Teach. 45, 294 (2007)
INTRODUCTION: The acceleration of a body is directly proportional to, and in the same direction as, the net force acting on the body, and inversely proportional to its mass’. This is Newton’s second law, that explains that a force acting on an object changes its state of movement. If a given object suffers a variation in its linear momentum, the force suffered by the object depends on the time period needed to do this variation.
OBJECTIVE: To verify experimentally Newton’s second law.
MATERIALS: a blanket, several eggs, a glass.
SETUP: Not required. A student will throw two eggs, with approximately the same initial speed. Other two students will hold the blanket in the air, picking up one egg carefully so that it will not break. The experiment can be also conducted by letting two eggs fall freely inside a glass, one empty and another filled with water, which will cushion the movement reducing the force on the egg.
EXPLANATION: Both eggs are thrown with the same initial speed and the linear momentum variation in both cases is the same as the final value is zero. The egg thrown against the blanket changes its momentum over a ‘large’ period of time so that the force experimented is small, while that thrown against the floor is stopped instantaneously producing a very strong force on it.
CONCEPTS: impulse or linear momentum, inertial mass, Newton’s laws of motion.
- T. Moore. Física seis ideas fundamentales, Mc Graw Hill, 2005.
- R. Serway, Física, Mac Graw Hill, 2010.
- P. Tipler, Física para la Ciencia y la tecnología , Reverté, 2012.
- R. Ehrlich, Turning the World Inside Out and 174 Other Simple Physics Demonstrations, Princeton University Press, 1997.
STUDENTS 2011-2012: Rosalía Carrillo, David Camino, Enrique Braña
LINK pdf STUDENTS (in Spanish):