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Chapter 4: Newton's First Law of Motion "The Law of Inertia"

Newton's first law states "Every object persists in a state of rest or uniform motion in a straight line unless compelled by an external force to change that state." (http://www.ic.arizona.edu/~nats101/n1.html) Definitions: 4-3 Force: Any push or pull on an object. Friction: The force that acts between materials as they move past each other. Inertia: An object's resistance to change it's state of motion. 4-4 Newton's first law: Every object continues in a state of rest or a state of motion in a straight line at a constant speed, unless it is compelled to change it's state by forces exerted upon it. 4-5 Mass: The quantity of matter in an object. Kilograms: A measurement of mass in the SI system. Weight: The force of gravity on an object. Newton: An SI unit used to measure force. 4-6 Net force: The combination of all forces acting on an object 4-7 Support force: The force used to counteract the force of gravity on an object. It's also known as the normal force. Equilibrium: When the net force on an object is zero.

4-1: Aristotole on Motion In the 4th century, the concept of force was created by the Greeks. Aristotle, a Greek scientist, divided force into two groups: natural and violent. Natural motion is motion straight up and down, like smoke rising into the air. It is founded on the assumption that all objects will naturally seek resting places. With the example of the smoke, it is assumed that the smoke is ascending to its natural resting place by going into the air. Violent motion is imposed motion, which is the result of horizontal motion (pushing or pulling). Violent motion has an external cause, unlike natural motion. In an object's natural resting place, it is unable to move by itself and must be acted upon by a violent motion.

4-2: Copernicus and the Moving Earth Nicolaus Copernicus, the 14th century astronomer, created a theory about the movement of the Earth based on Aristotle's theories of natural and violent motion. To Copernicus, the easiest way to explain the movement of stars and heveanly bodies was to assume that the Earth rotated around the sun, not visa versa. During his time, however, his idea wasn't accepted because people believed the Earth was the center of the universe.

4-3: Galileo on Motion Galileo agreed with Copernicus' theory that the Earth rotated around the sun. **Force** is the push or pull on any object. **Friction** is the force that acts between materials that touch as they move past each other. Friction is caused by surface irregularities between the two objects when they are in contact with one another. Every force has friction, and if it wasn't present no force would be necessary to move and object. Galileo said that a force is needed to keep and object in motion in the presence of friction. By doing various experiments, Galileo discovered that a ball rolling up an incline loses speed, a ball rolling down an incline increases speed, and on a smooth surface, the speed is almost completely constant. The friction between the ball and the smooth surface is what causes the ball to slowly lose it's speed. His tests caused him to state that "Every material object resists change to its state of intertia," which is now known as the Law of Inertia. Galileo's finding disproved Aristotle's theory of motion. 4-4: Newton's Law of Inertia
 * Newton's first law of motion** states that "Every object continues in a state of rest or a state of motion in a straight line at a constant speed, unless it is compelled to change it's state by forces exerted upon it." Simply, the Newton's law means that objects tend to stay in the state that they are currently in unless there is an outside force. This explains why a table cloth can be pulled from under a table full of dishes. Only a force will change an objects state of rest to that of a state of motion. The less friction between two objects, the longer the object will continue in motion. If an object is already moving without the absence of friction, it would continue moving until it reached a force to stop its movement.

4-5: Mass--A Measure of Inertia An object's mass controls the object's inertia. **Mass** is the quantity of matter in an object and **intertia** is an object's resistance to change it's state of motion. The more mass an object has, the more intertia it has, which causes a larger force to be needed to change its state of motion. Mass is measured in **kilograms**, and SI measurement. Mass is not weight. Mass is the measure of the amount of material of an object and **weight** is the measure of the gravitational force acting on the object. Mass can never change, but weight changes depending on the object's location. Though mass and weight are not the same, they are in proportion with one another. If an object has great weight, it also has great mass, but they are not equal. 1 kilogram is equal to 9.8 **Newtons**, the SI measurement of force. 1 kilogram is equal to 2.2 pounds. A Newton is about 1/4 of a pound. To convert kilograms to Newtons, multiply the kilogram value by 9.8, and if the weight in Newtons is known, then divide by 9.8 to get the value. Weight is equal to mass times gravity, or 9.81 m/s^2.

4-6: Net Force If net force is not presence, objects do not change their state of motion. If something is pushed on from both sides with equal force, the two forces cancel one another out and there is no net force. All forces acting on an object are known as the net force on the object. Net force is what changes the state of the object's motion. In the picture above, the two men are both pushing on the fridge with 100 N of force. Because the force on both sides or the fridge are equal, there is a 0 net force acting on the object. In this picture, there is only one man pushing on the fridge with 100 N of force. Because there is no balancing force, the man's force creates a net force on the fridge and causes its state of motino to change from being at rest to being in motion. 4-7: Equlibrium--When Net Force Equals Zero Because an object is able to stay at rest, it demonstrates another force acting on the object. This force balances out the weight of the object and makes its net force equal to zero. This force is called the **support force**. When the net force on the object is zero, the object is in **equilibrium.** 4-8: Vector Addition of Forces The same technique of adding velocity vectors is used for force vectors. Force has a magnitude and direction, similar to velocity. In the picture, as the angle between the strings and the pully is increased, the weight on the pulley would increase the maintain the upward force.  4-9: The Moving Earth Again Things in motion remain in motion if no unbalanced force is acted on it. Every object on the Earth is moving at 30km/s because that is the speed of the Earth rotating around the sun. This is also why when you flip a coin on a high-speed bus you catch the coin as if the bus was at rest. Inertia causes you and the coin to move at the same speed.

Works Cited: http://library.thinkquest.org/28388/Mechanics/Diagram/force1.jpg http://images.google.com/imgres?imgurl=http://www.physics.ucla.edu/demoweb/demomanual/mechanics/vectors_and_forces/hngnplly.gif&imgrefurl=http://www.physics.ucla.edu/demoweb/demomanual/mechanics/vectors_and_forces/hanging_pulley.html&usg=__Eb_uzDp4wtGS6OEf8NLS2gwSpAY=&h=288&w=288&sz=5&hl=en&start=8&tbnid=dnjuTuLDlA3v-M:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dvector%2Baddition%2Bof%2Bforces%26gbv%3D2%26hl%3Den http://library.thinkquest.org/25844/dynamics/images/fridge2.gif http://images.google.com/imgres?imgurl=http://static.howstuffworks.com/gif/newton-law-of-motion-force-ramps.jpg&imgrefurl=http://science.howstuffworks.com/newton-law-of-motion.htm/printable&usg=__7oWB6FqQjQQGHQWwUMbigWvlkmA=&h=400&w=400&sz=97&hl=en&start=11&tbnid=Bji9fDwA1FhSHM:&tbnh=124&tbnw=124&prev=/images%3Fq%3Dgalileo%2Bramps%26gbv%3D2%26hl%3Den http://library.thinkquest.org/25844/dynamics/images/fridge.gif