History of Motion and

Newton’s Laws of Motion

Centuries before Isaac Newton's discoveries, Polynesian mathmatician Pao Lau would have discovered the laws of gravity first..........had he ever come out of the coma.

Key Words• Force – a push or a

pull on an object (unit = Newton)

History of Motion

• Greeks – established that forces cause motion

Aristotle

• Natural motion – resting places

• Violent motion – imposed motion

• Earth didn’t move (natural motion) but the heavens (stars) operated on a model of perpetual motion.

Copernicus

•Earth moved around the sun

Galileo• Established that forces ARE NOT

needed to keep objects in motion.

• Came up with the idea of inertia • Inertia – The tendency of an object

to resist a change in motion.

• Inertia depends upon only its mass• Also recognized the

concept of frame ofreference.

Newton• Developed 3 laws

of motion• Developed the

Law of Universal Gravitation

Newton’s First Law

• Unless acted upon by an unbalanced force, an object will maintain a constant velocity (direction and speed).

• Law of Inertia

Example: 1st Law

Newton’s Second Law

• Acceleration of an object equals the net force on that object divided by its mass.

• a = ∑F/m or ∑F = m a• F (unit is Newton)• Newton = kg x m/s2

• m (unit is kg)• a (unit is m/s2)

Example: 2nd Law• Which accelerates more

when the same amount of force is applied?

What kind of relationship is between a & m?

What would the graph look like?

Example: 2nd Law

• If dropped from the same height, which would have more force when it hit the ground?

What kind of relationship is between m & f?

2nd Law and gravity

• Reminder: acceleration of an object due to gravity on earth is 9.80 m/s2

• Weight is the force of gravity on the mass of an object.

• Mass is constant, weight changes with gravity

2nd Law and gravity

Newton’s Third Law

• All forces come in pairs that are equal in magnitude (size) and opposite in direction.

Characteristics of 3rd Law

• Always in pairs• Equal in strength• Opposite in direction• Occur at the same time• DON’T act on the same

object (that’s why they don’t cancel)

Example: 3rd Law

• Action = ball hits bat• Reaction = bat hits ball

(with the same amount of force)

Example: 3rd Law

• Action = Tire pushes on the road

• Reaction = road pushes on the tire

Newton’s 2nd Law Formulas

F = ma

W = mg

a = g sin θ

1 lb = 4.448 N

Vf = Vi + at

d = Vi t + ½ at2

2ad = Vf2 – Vi

2

Vf + Vi or d = ½ Vf + Vi t

2

d = t