Chapter 2: Newton’s Laws of Motion

2.1 Newton’s First Law of Motion

2.2 Newton’s Second Law of Motion

2.3 Forces and Interactions

2.4 Newton’s Third Law of Motion

2.5 Vectors

2.1 Newton First Law of Motion

• Law of Inertia: Every object continues in a state of rest, or in a state of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted on it.

• The Moving Earth

The moving earth

• Copernicus: published a book (1543) proposing that the earth revolved around the sun. Sun-centered solar system

-Popular view: Earth is the center of the universe

• Argument against moving earth: a bird catching a worm would be an impossible task.

2.2 Newton’s Second Law of Motion

• “The acceleration produced by a net force on an object is directly proportional to the net force, is in the same direction as the net force, and is inversely proportional to the mass of the object”.

Non-Free Fall

Is acceleration equal to g?

2.3 Forces and Interactions

• Force is interaction between one thing and another; pairs of forces acting on two different objects. The two forces make up a single interaction.

• Both forces are equal and opposite.

In which case the fist stops?

2.4 Newton’s Third Law of Motion

• “ whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first”

• (one force is called the action force and the second is the reaction force)

• “To every action there is always an opposed equal reaction”

examples

Action and Reaction on Different Mases

Defining Your system

• Action and reaction forces are equal and opposite, why don’t they cancel?

• A forces external to a system is needed to accelerate it.• Internal forces do cancel each other

Pair: friction and pull

2.5 Vectors

2.5 Vectors