Newton’s First Law of Motion

Newton’s First Law of Motion

Sections 2.4 and 2.5Sections 2.4 and 2.5

ObjectivesObjectives

At the end of class today:

You will be able to explain that motion is based on a frame of reference.

You will be able to define and apply Newton’s Law of Inertia.

At the end of class today:

You will be able to explain that motion is based on a frame of reference.

You will be able to define and apply Newton’s Law of Inertia.

2.4 Motion is Relative2.4 Motion is Relative

Motion is looked at through its relationship to something else.

Motion is relative to a frame of reference.

A frame of reference is a set of principles or criteria through which things are given a specific meaning.

Motion is looked at through its relationship to something else.

Motion is relative to a frame of reference.

A frame of reference is a set of principles or criteria through which things are given a specific meaning.

2.4 Motion is Relative2.4 Motion is Relative

Examples:

When talking about a space shuttle moving at 30,000 km/h, that speed is relative to the Earth below.

Speed is often relative to the surface of the earth.

Examples:

When talking about a space shuttle moving at 30,000 km/h, that speed is relative to the Earth below.

Speed is often relative to the surface of the earth.

2.4 Motion is Relative2.4 Motion is Relative

Example:

Think of looking at a car traveling 65 mph on a highway:

Relative to you in a car traveling the 55 mph

Relative to you standing on the side of the road.

Example:

Think of looking at a car traveling 65 mph on a highway:

Relative to you in a car traveling the 55 mph

Relative to you standing on the side of the road.

2.5 Newton’s 1st Law - The Law of Inertia

2.5 Newton’s 1st Law - The Law of Inertia

Newton extended Galileo’s concept of inertia and gave it the status of a law that pertains to all motion.

Aristotle’s ideas of motion were put to rest for good.

Newton extended Galileo’s concept of inertia and gave it the status of a law that pertains to all motion.

Aristotle’s ideas of motion were put to rest for good.

2.5 Newton’s 1st Law - The Law of Inertia

2.5 Newton’s 1st Law - The Law of Inertia

Newton’s First Law -

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 upon it.

Newton’s First Law -

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 upon it.

2.5 Newton’s 1st Law - The Law of Inertia

2.5 Newton’s 1st Law - The Law of Inertia

In plain language - Things tend to keep on doing what they are already doing.

Objects at rest tend to stay at rest

a force is needed to set them in motion

Fig. 2.8 Pg. 23 - Dishes & Tablecloth example

In plain language - Things tend to keep on doing what they are already doing.

Objects at rest tend to stay at rest

a force is needed to set them in motion

Fig. 2.8 Pg. 23 - Dishes & Tablecloth example

2.5 Newton’s 1st Law - The Law of Inertia

2.5 Newton’s 1st Law - The Law of Inertia

Objects in motion tend to stay in motion along a straight line path

Once moving, no force is needed to keep the object moving (other than any force needed to overcome friction)

Figure 2.9 pg. 23

Objects in motion tend to stay in motion along a straight line path

Once moving, no force is needed to keep the object moving (other than any force needed to overcome friction)

Figure 2.9 pg. 23