CHAPTER 3: INERTIA 1. Purpose of Experiments with Inertia 2. Inertia 3. Experiments with Inertia 4. Other Activities 5. The Importance of Inertia 6. Bibliography 7. Research Topics Montessori Research and Development 2004 26
1. Purpose of Experiments with Inertia The children have already done several experiments with inertia from the Functional Geography manual. More experimentation will result in a greater understanding of the force of inertia and how it affects the movement of objects. 2. Inertia Inertia is the property of matter that causes it to resist any change of its motion in either direction or speed. Sir Isaac Newton developed three laws of motion. The first law of motion states than an object at rest tends to stay at rest, and an object in motion tends to continue in motion in a straight line unless acted upon by an outside force. Experiments 3A, 3B, and 3C in the Functional Geography manual demonstrate the first part of this law. The inertia of an object is determined by its mass. The second law of motion states that a force acting on an object is equal to the mass of the object multiplied by the acceleration the object undergoes. The body experiences an acceleration in the direction of the force and proportional in amount to it, as well as inversely proportional to the mass of the body. When the same force is applied to objects of different masses, the less massive object will move farther than the more massive object. If two objects of different masses are to accelerate at the same rate, more force must be applied to the more massive object to get the same acceleration. Montessori Research and Development 2004 27
The third law of motion states that associated with every force, there is an equal and oppositely directed reaction force. For every action, there is an equal and opposite reaction. An example of this law is what happens to packages in moving vehicles. When the vehicle moves forward from a stopped position, the packages move backward. When a vehicle backs up, the packages move forward. Montessori Research and Development 2004 28
3. Experiments with Inertia Levels I - III Resistance to Change in Motion Question: What happens to objects when the vehicle in which they are travelling stops suddenly? Hypothesis: The objects will continue moving in the direction that the vehicle was travelling. Materials: several books chair on wheels Procedure: 1. Place the stack of books on the edge of the chair. 2. Move the chair forward, then stop suddenly. 3. Replace the books, move the chair backward, and stop suddenly. 4. Observe. Observations: When the chair was moved forward and stopped suddenly, the books continued to move forward and fell to the floor. When the chair was moved backward and stopped suddenly, the books continued to move backward on the chair seat. Conclusions: An object in motion tends to stay in motion unless an outside force acts upon it. The books were in motion with the chair and continued to move even when the chair was stopped because they were not attached to the chair. This happened for both forward and backward movement. Montessori Research and Development 2004 29
Discussion: This is a demonstration of Newton s first law of motion that states in part than an object in motion tends to continue in motion in a straight line unless acted upon by an outside force. In both cases, the books continued moving in the direction the chair was moving even though the chair was stopped. They would have continued moving in a straight line, except that outside forces prevented this from happening; gravity pulled them down to the floor in the forward demonstration and friction stopped them in the backward motion. Montessori Research and Development 2004 30
Levels IV - VI Objects in Motion Question: What happens to objects that are not in restraints when a car hits a wall? Hypothesis: The objects will continue moving after the car stops. Materials: toy car wood ruler modeling clay 2 thick books thin board about 2 feet long masking tape Procedure: 1. Place one book on a table and position one end of the board on top of the book. 2. Tape the other end of the board to the table. 3. Tape the wooden ruler to the table about 6 inches from the end of the board and perpendicular to it. 4. Make a clay figure. Carefully place it on the hood of the car. 5. Place the car at the top of the board and release the car so that it rolls down the board and hits the ruler. Observe. 6. Measure the distance the clay figure falls from the car. 7. Repeat this procedure several times. 8. Add another book. Repeat the above procedure. Observations: When the car hit the ruler, the clay figure continued to move forward because it was not attached to the car. The faster the car moved, the farther the clay figure fell from the car. Montessori Research and Development 2004 31
Conclusions: An object in motion tends to stay in motion unless acted upon by an outside force. When the car stopped, the clay figure continued to move in the same direction because it was not attached to the car. Gravity was the force that acted upon the clay figure and pulled it to the table top. When two books were used to increase the height, the car was able to accelerate more quickly and move faster. When the car stopped, this increase in acceleration was demonstrated when the clay figure fell farther from the car. Discussion: The car gains speed or accelerates as it travels down the board. The clay figure is moving at the same speed. When the car is stopped, the clay figure continues to move forward in a straight line at the same speed, until gravity pulls it down to the table top. When the height was increased, the speed of the car and the clay figure also increased. When the car stopped, this increase in speed allowed the clay figure to travel farther from the car. Both the car and clay figure have inertia, a resistance to change in motion. These objects in motion would continue in motion in a straight line unless an outside force acted upon them. The ruler was the outside force acting upon the car. The clay figure continued in motion until gravity pulled it down to the table top. Montessori Research and Development 2004 32
4. Other Activities The children may develop other experiments to demonstrate inertia. They may use experiment books to find experiments to demonstrate inertia to the class. 5. The Importance of Inertia Inertia is one of the forces involved in the formation of the universe. By performing experiments that demonstrate inertia, we develop a better understanding of how this force was necessary for the formation of the planets, moons, stars, etc. These celestial bodies will continue their present motion unless outside forces act upon them. 6. Bibliography Physics for Every Kid by Janet VanCleave; ISBN 0-471-52505-7 7. Research Topics A. Important People Sir Isaac Newton Montessori Research and Development 2004 33