PHYSIC 300 LAB Report - Coursework Example

Physics 300 Lab report: Action – Reaction The relationship, F = ma, was investigated in this experiment to demonstrate the validity of the action – reaction law, also known as the Newton’s third law. This was carried out by changing the mass attached to a balloon in motion while observing the speed under the different masses. In this experiment, balloon, straw, scotch tape, monofilament and washer were used. A cut straw measuring 1.5 inches was mounted and secured on the middle part of the inflated balloon with one end of the straw was aligned with opening of the balloon.

Five pennies were attached at the central part of the bottom of the balloon. A taut monofilament, which ran to the other end of the room, was threaded through the straw attached to the balloon. This was followed by releasing the hand-sealed balloon opening to launch the balloon into motion. The speed of the balloon was noted. The experiment was, respectively, repeated with ten pennies and ten Yen coins. The results of the experiment, indeed, validated the law of action – reaction, which states that to every action there is always opposed and equal reaction due to conservation of momentum.

Simply put, if a body A exerts a force F on a body B, body B simultaneously exerts a force F of the same magnitude on body A provided both bodies are acting along the same line. Thus, as observed in our experiment, the balloon, by releasing the pressure inside, was launched into motion with a momentum that changes in proportion to the force exerted. The moving balloon exerted this force on the attached pennies/coin, as the case maybe. Following the law of action and reaction, the pennies/coin exerted a force of the same magnitude on the balloon but in the opposite direction.

We observed that as the number of the pennies increased from five to ten, which correspondingly increased the mass, the acceleration of the balloon decreased. Conversely, changing from ten pennies to ten Yen coins (Yen coins are lighter than pennies) increased the acceleration of the balloon. This observation indeed validated the law of action – reaction given that the total momentum of the balloon-pennies/coin system is conserved and that the force remains constant irrespective of the total mass of the system; only a change in the acceleration of the system will ensure that the momentum remains conserved.

Answers to questions 1. By pushing against the water with a force, the swimmer is thrust forward (in the opposite direction) with a force of the same magnitude with which he/she pushes against the water. 2. The gas released from the jet nozzle thrust the jet forward with a force equal in magnitude to the force in which the gas is released. 3. As the water gushes out of the nozzle, it pushes the fire hose backward with a force equal in magnitude to the force with which the water gushes out. The action force is as a result of the mass and the speed (more appropriately acceleration) of the water while the reaction force is the backward force exerted on the fireman.

Center of Mass In this experiment, we aimed at locating the center of mass of different objects by using a cardboard, string, scissors and scotch tape. Briefly, an irregular shape was cut out of the cardboard and a piece of string was taped along the edge of the cut object, with the object hanging freely on the vertical surface. A straight line defined by the string was drawn across the object. Subsequently, two other straight lines were drawn across the object following the path defined by the strings attached to two other positions along the edge of the object.

The intersection of the three lines gave the center of mass of the object. This was followed by making a tiny hole at the center of mass of the object, passing the string through the hole, taping the string to the other end of the object and suspending the object by the string. Given that the net torque at the center of mass is zero, the object was nicely balanced. The experiment was repeated with shapes corresponding to the letter C and the map of continental USA. Answers to questions 1. The center of mass of the letter C was not within the frame of the letter (was in air) and so the letter could not be balanced. 2. The center of mass of the map of continental USA was in Nebraska. 3. You fall because the center of mass is no longer direct above our feet (the net torque is not equal to zero).