1. Newton’s laws of motion
CH & 12.3

2. ARISTOTLE, GALILEO, AND NEWTON
All modern scientists have an understanding of the relationship between force and motion, but it took about 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)

3. ARISTOTLE, GALILEO, AND NEWTON
Galileo Galilei (1564 – 1642)
Italian scientist
Work with gravity helped correct misconceptions about fore 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

4. 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.

5. 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

6. 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?

7. 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)

8. 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.

9. 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.

10. 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.

11. 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