Newton’s laws of motion CH. 12.2 & 12.3

ARISTOTLE, GALILEO, AND NEWTON All modern scientists have an understanding of the relationship between force and motion, but it took about 2000 years of study to develop this understanding. The work of scientists such as Aristotle, Galileo, and Newton proved essential in developing our understanding of the natural world. Aristotle (384 B.C. – 322 B.C) Greek scientist and philosopher Made many discoveries through careful observation and reasoning Proposed incorrect theory that force is needed to keep object moving at constant speed, a concept that hindered study of motion. (shows how the validity of science is relevant to the time/current understanding and subject to failures)

ARISTOTLE, GALILEO, AND NEWTON Galileo Galilei (1564 – 1642) Italian scientist Work with gravity helped correct misconceptions about force and motion that had been widely held since Aristotle’s time Concluded that moving objects not subject to gravity/friction will move indefinitely (think of things moving in outer space) Isaac Newton (1643 – 1727) English mathematician, astronomer, and physicist Developed the three laws of motion that form the basic principles of modern physics Discovered calculus

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 ZERO. First law also known as Law of Inertia – tendency for an object to resist change in its motion. An object at rest will remain at rest or an object in motion will remain in motion unless acted upon by an unbalanced force. https://www.youtube.com/watch?v=tMN36z8Zz4U

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. Mass – measure of the inertia of an object and depends on the amount of matter the object contains. Acceleration = Net Force or a = F/m Mass

Newton’s second law of motion An automobile with a mass of 1000 kg accelerates when the traffic light turns green. If the net force on the car is 4000 newtons, what is the car’s acceleration?

Weight and mass It is important to understand that weight and mass are NOT the same thing. Mass – measure of the inertia of an object Weight – measure of the force of gravity acting on an object Weight = Mass x Acceleration due to gravity ( W = mg) m = mass g = acceleration due to gravity (on Earth g = 9.8 m/s^2)

Newton’s third law of motion Whenever on object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. These two forces are called action and reaction forces.

Newton’s third law of motion Pressing your hand against a desk or wall exerts an action and reaction forces. Action force – force exerted by your hand on the wall Reaction force – force exerted by the wall in equal and opposite direction Action-Reaction Forces DO NOT Cancel – forces may not act on the same object. Only when equal and opposite forces act on the same object do they cancel.

Momentum Momentum = Mass x Velocity Momentum – product of an object’s mass and its velocity. Momentum = Mass x Velocity An object has a large momentum if the product of its mass and velocity is large. The momentum of any object at rest is zero.

What happens to momentum when objects collide? Under certain conditions, collisions will obey the Law of Conservation of Momentum. The law states – in a closed system, the loss of momentum of one object equals the gain in momentum of another object – momentum is conserved. Conserved – to maintain constant value https://www.youtube.com/watch?v=2UHS883_P60