Question

how can you prove newtons third law of motion by using two spring balances given to you.

Answer 1

 Newton’s Third Law Atomic Springs- When you push against a wall, you feel a force in the opposite direction. The harder you push, the harder the wall pushes back on you. The amazing fact is that the force exerted by the wall on you is exactly equal and opposite to your push. How does the wall “know” to push this way? In general how can inanimate objects, such as walls, floors, and tables, push and pull other objects? The answer lies in the atomic world. Solids are made of atoms held together in a lattice structure by electric forces (atomic bonds). Physicists view solids as a set of balls (atoms) connected by springs (bonds): The length of one “atomic spring” is about one nanometer (10−9 m). The number of atoms in a typical solid such as a book or a table is about 1,000,000,000,000,000,000,000,000 ! When you push on a solid, the atomic springs compress, i.e., the electron clouds of the atoms overlap. The harder you push, the more the springs compress, and thus the harder the springs push back on you. What you actually “feel” is the electric repulsion between the atoms in the surface of the solid and the tip of your finger. On a larger scale, it is similar to the magnetic repulsion you feel when you push one magnet toward another magnet. It is important to realize that nothing actually “touches” when two objects come into “contact”, i.e., when you push on something. If two atoms actually touched – one nucleus on top of another nucleus – then nuclear fusion would result thereby creating an atom-bomb explosion! Force fields touch, not ponderable matter. Again, think about two magnets repelling at a distance. This “atomic springiness” endows matter with an elastic property. When you put a book on the table or push on the wall, the surface of the table and the wall bend slightly (greatly exaggerated in the picture below). Think of putting a bowling ball on a mattress (box springs). Newton’s Third Law – Version 1.0 Force on Table FTB due to Book FBT Force on Book due to Table The “bent” table acts like a compressed spring that exerts a force back on the book. The “action” of pushing forward creates a “reaction” of pushing backward. Not all solids are elastic. Materials such as clay, putty, and dough, are inelastic – they do not “spring back” after they have been compressed or stretched. Action and Reaction Qualitatively speaking, a force is a ‘push’ or a ‘pull’. Rigorously speaking, a force is an interaction between two objects. This interaction obeys a deep law of mechanics: Newton’s Third Law: If one object exerts a force on a second object, then the second object exerts an equal and opposite force on the first. In symbols, F12 = − F21 . Notation: F12 ≡ Force on object 1 due to object 2. F12 ≡ Force on object 2 due to object 1. All forces come in pairs. For every “action”, there is an equal and opposite “reaction”. You cannot have a single force in any situation because the force on one object is always due to some other object. Here are some examples of interactions (pairs of forces): Action Reaction You push back on Floor Floor pushes forward on You (explains how a person walks) Tires push back on Road Road pushes forward on Tires (explains how a car moves) Rocket pushes back on Gas Gas pushes forward on Rocket (explains how a jet moves) Book pushes down on Table Table pushes up on Book Earth pulls down on Moon Moon pulls up on Earth Magnet pulls left on Nail Nail pulls right on Magnet