Newton’s First Law of Motion Sections 2.4 and 2.5

Objectives 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 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 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 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 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 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 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 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 Dishes & Tablecloth example

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