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# Newton's First and Second law

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on 23 October 2013

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#### Transcript of Newton's First and Second law

Newtons Second Law of Motion
How do unbalanced forces affect the motion of an object? Well, an unbalanced force causes an object's velocity to change or the object accelerates. According to Newton's second law of motion, the acceleration of an object is equal to the net force acting on it divided by the object's mass. Thus doubling the mass of an object cuts its acceleration in half.
Acceleration= Net force/Mass
Newton's First and Second Laws of Motion
The Big Three
Aristotle
Galileo
Newton
Newton's First Law of motion
According to Newton's first law of motion, the state of motion of an object does not change as long as the net force acting on the object is 0. >Thus, unless an unbalanced force acts, an object at rest remains at rest and an object in motion stays in motion with the same speed and direction.<
Key Concepts
1. How does Newton's first law relate change in motion to a zero net force?

2. How does Newton's second law relate force, mass and acceleration?

3. How are weight and mass related?
Aristotle (384b.c.-322b.c.)
Greek scientist and philosopher; Aristotle made many scientific discoveries through careful observation and logical reasoning. He incorrectly proposed that force is required to keep an object moving on at a constant speed. This error held back 2,000 years of progress in the study of motion.
Clique: Plato, and Socrates.
Galileo Galilei (1564-1642)
Italian scientist experimented to found out about the world. By rolling balls down wooden ramps, he studied how gravity produces constant acceleration. He concluded that moving objects not subjected to friction or any other force would continue to move inordinately
Isaac Newton (1642-1727)
When the plague broke out in London, forcing him to leave Trinity College in Cambridge, England. The next 2 years he built on the work of scientists such as Galileo. He published his results many years later entitled Principia.
Examples
A soccer ball resting on the grass remains motionless until a force is applied to it in the form of a kick. The kicked ball begins rolling. Because friction between the grass and ball acts on the ball as it rolls, the ball slows. The force of friction slows the ball and brings it to a stop.
Law of Inertia
Inertia is the tendency of an object to resist a change in its motion. In other words, an object at rest tends to remain at rest, and an object in motion tends to remain in motion with the same direction and speed.
Note that when the soccer ball was at rest the forces acting on it was balanced
Examples
You apply net force to a ball when you throw it. The harder you throw, the more the ball accelerates. In fact, the acceleration of the ball is directly proportional to the net force acting on it. If you double the force, the acceleration of the ball doubles as well.
Mass
Newton learned that the acceleration of an object depends upon its mass. Mass is measure of the inertia of an object and depends on the amount of matter the object contains.
Weight and Mass
Weight and mass are not the same thing. Weight is the force of gravity acting on an object. An object's weight is the product of the object's mass and acceleration due to gravity acting on it. The weight formula is basically Newton's second law. However weight is substituted for force and acceleration due to gravity is substituted for acceleration. Mass and weight are proportional. Doubling the mass of an objects also doubles its weight. Mass is a measure of the inertia of an object; weight is a measure of the force of gravity acting on an object.
Example
On the moon, the acceleration due to gravity id only about one sixth that on Earth. Thus, the astronaut weighs only about one sixth as much on the moon as on Earth. In both locations, the mass of the astronaut is the same.