NEWTON’S LAWS OF MOTION

Sir Isaac Newton (1642 – 1727)

Newton was an English physicist, considered one of the most important scientists of all time. Newton formulated laws of universal gravitation and motion—laws that explain how objects move on Earth as well as through the heavens. He established the modern study of optics—or the behavior of light—and built the first reflecting telescope.

Forces

• A force is a push or a pull.• In honor of Newton’s work with

motion, the unit of force in the metric system is named for him.

• One newton is the amount of force it takes to accelerate a one kilogram mass at a rate of 1 meter/second 2.

• 1 n = 1kg-m/s2

Newton’s First Law (Part 1)(Law of Inertia)

An object at rest remains at rest unless acted on by an outside (unbalanced) force.

Weight and Mass• Weight is the force

with which gravity pulls an object downward.

• Units:– Metric – Newton (n)– English – pound (lb)

• Varies depending on the object’s location

• Mass is the amount of matter contained in an object.

• Units:– Metric – kilogram

(kg)– English - slug

• Remains constant

Newton’s First Law (Part 2)

• An object in motion remains in motion unless acted on by an outside (unbalanced) force.

• What does it take to keep an object in motion (ignoring friction)?

Both the car and its driver are traveling at 30 mph. When the car stops suddenly, the driver continues at 30 mph. Why?

Newton’s Second Law

• If there is an unbalanced force, there will be an acceleration.

• The size of the acceleration depends on– the mass of the object– the size of the force

• This is usually written F = ma or a = F/m

Larger Forces Cause Larger Accelerations

Mass: 1545 kg

Horsepower: 395 hp

0 – 60 mph: 4.5 s

Mass: 1545 kg

Horsepower: 192 hp

0 – 60 mph: 8.4 s

Larger Masses Cause Smaller Accelerations

Baseball mass = 0.14 kg (.32 lbs)

Distance = over 90 m (300 ft)

Shot put mass = 7.26 kg (16 lbs)

Distance = 23.12 m (75 ft)

Newton’s Third Law(Law of Action – Reaction)

• For every action there is an equal and opposite reaction.

• If object A exerts a force on object B then object B exerts an equal force in the opposite direction on object A.