N E W T O N ’ S L AW S O F M O T I O N

CHAPTER 3 NOTES

NEWTON’S LAWS OF MOTION

• Isaac Newton, born 1642, developed 3 laws of motion which overthrew Aristotle’s ideas about motion.• These 3 basic laws of motion help us understand everything we know about the way things move.

NEWTON’S FIRST LAW OF MOTION

•Newton’s First Law States: •Every object continues in its state of rest, or a uniform speed in a straight line, unless acted on by a nonzero force.

NEWTON’S FIRST LAW OF MOTION

• In other words:• an object at rest remains at rest unless acted

on by an outside force.• An object in motion remains in motion unless

acted on by an outside force.

NEWTON’S FIRST LAW OF MOTION

• Inertia= the property of objects to resist changes in motion.

NEWTON’S FIRST LAW OF MOTION

• Video clip

NEWTON’S SECOND LAW OF MOTION

•Newton’s Second Law of Motion states: 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.

NEWTON’S SECOND LAW OF MOTION

• In other words:• Acceleration is produced when a force acts on a

mass. • The greater the mass of the object, the greater

the force needed to accelerate it.

NEWTON’S SECOND LAW OF MOTION

• The equation we use to represent Newton’s Second Law of Motion is F=ma• F=Force, in Newtons (N)•m=mass, in kilograms (kg)• a=acceleration, in meters per second per second (m/s/s)

NEWTON’S SECOND LAW OF MOTION

• An object accelerates in the direction of the net force acting upon it.

NEWTON’S SECOND LAW OF MOTION

• Newton’s second law of motion also explains why objects of different masses fall at the same speed.

NEWTON’S SECOND LAW OF MOTION

• Falling objects accelerate toward Earth because of the force of gravity.

NEWTON’S SECOND LAW OF MOTION

• When there is little to no air resistance slowing down a falling object, we say it is in free fall.

NEWTON’S SECOND LAW OF MOTION

• Objects in free fall accelerate toward Earth at 9.8 m/s/s.

NEWTON’S SECOND LAW OF MOTION

• Usually, air resistance is not negligible for a falling object-it works against a falling object to slow it down.

NEWTON’S SECOND LAW OF MOTION

• When enough air resistance builds up to equal the weight of a falling object, the object reaches terminal speed or terminal velocity.

NEWTON’S SECOND LAW OF MOTION

• Terminal speed for a human skydiver is 150 km/hr-200 km/hr!

FORCES AND INTERACTIONS

Forces are not only pushes or pulls-they are interactions.

• For example, if you push on a wall, the wall is simultaneously pushing back on you.

FORCES AND INTERACTIONS

• Net Force= The total force in a given direction that results from two or more interacting forces.

3 N9 N

6 N

FORCES AND INTERACTIONS

5 N 12 N

? N

7 N to the left

NEWTON’S THIRD LAW OF MOTION

Newton's third law states:

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

NEWTON’S THIRD LAW OF MOTION

• In other words, every action has an equal and opposite reaction.

NEWTON’S THIRD LAW OF MOTION

Foot exerts force on ground

Ground exerts force on foot

NEWTON’S THIRD LAW OF MOTION

Tires push on roadRoad pushes on tires

NEWTON’S THIRD LAW OF MOTION

Action: Object A exerts a force on object B.

• Reaction: Object B exerts a force on object A.

NEWTON’S THIRD LAW OF MOTION

Action: Foot exerts force on ground

Reaction: Ground exerts force on foot

NEWTON’S THIRD LAW OF MOTION

Action: Tires push on road Reaction: Road pushes

on tires

EXCEPTIONS TO NEWTON’S 3 LAWS

• Objects moving near the speed of light.

EXCEPTIONS TO NEWTON’S 3 LAWS

• Objects that are very, very small-on the scale of an atom.

EXCEPTIONS TO NEWTON’S 3 LAWS

• Objects under the influence of very strong gravitational forces.

REVIEW

1. A karate chop delivers a force of 3000 N to a board that breaks. The force that the board exerts on the hand during this event is:

• A. less than 3000 N

• B. 3000 N

• C. greater than 3000 N

• D. Need more information

REVIEW

2. What kind of path would Earth follow if suddenly its attraction to the Sun no longer existed?

• A. The Earth would continue in its same path, but at a reduced speed.

• B. The Earth would continue traveling in its same path, but at a greater speed.

• C. The Earth would move in a straight line with constant speed.

• D. The Earth would spiral toward the Sun.

REVIEW

3. Newton's Second Law of Motion states:

A. Every object continues in its state of rest, or a uniform speed in a straight line, unless acted on by a nonzero force.

B. 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.

C. Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

D. None of the above.