Newton’s Laws of Motion

Forces cause changes in motion.

Preliminary Question:• What do all of the following have in common?

Newton’s Laws of Motion

• Once an object is moving, no force is needed to keep it moving

• Only if friction is present, you need to push something to keep it moving

• Without friction, a moving object keeps on moving at constant velocity

Galileo on Motion

a. Ball rolls down - downward push (from gravity) – speed up

b. Ball rolls upward - downward push (from gravity) – slow down

c. Ball rolls on a level floor, the floor compensates for gravity, no push – constant velocity

Galileo on Motion

Galileo stated:Every object has this tendency to keep moving

without changing its motion if it was moving; or to remain at rest if it was at rest

The property of a body to resist changes to its state of motion is called inertia.

Mass – is a quantitative measure of an object’s inertia

Galileo on Motion

Our Experimental Evidence: Ball Lab

No push: ball rolls at constant velocity

Yes - PUSH: balls ACCELERATE

Forces cause changes in motion.

Newton’s First Law of Motion: Inertia• Every object continues in a state of rest, or of

uniform speed in a straight line, unless acted on by a nonzero net force.

Simply put, things tend to keep on doing what they’re already doing. – Objects in a state of rest tend to remain at rest. – Only a force will change that state.

Newton’s First Law of Motion: Inertia

Don’t let this be you. Wear your seat belt.

Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 km/hour.

Simply put, things tend to keep on doing what they’re already doing.

Objects in a state of motion tend to remain in motion with constant speed in a straight line. Only a force will change that state.

• Observe what happens to the crash dummies in the video. Explain using Newton’s First Law.

• Crash Test• Observe what happens to the curling stone in

the video. Explain using Newton’s First Law.• curling

Newton’s First Law of Motion

Newton’s First Law of Motion: Inertia

Newton’s First Law of Motion• Cruising airliner moves at constant velocity

because all forces acting on it are balanced

Newton’s Laws of Motion• All forces balance so the airliner

moves at constant velocity

• Unbalanced force from the club accelerates the

golf ball