Newtons First Law of Motion Inertia 1 st

Newton’s First Law of Motion Inertia

1 st Law Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces exerted upon it. Or… An object in motion tends to stay in motion, and an object at rest tends to stay at rest.

Thinking example #1 If the force of gravity between the sun and the planets suddenly disappeared, what type of path would the planets follow?

Thinking example #2 Using the first law of motion, describe why a person will hit their head on the windshield if they are not restrained with a seatbelt during a head-on collision.

Thinking example #3 Using the first law of motion, describe whiplash.

Water bottle activity Place a piece paper below a filled water bottle. Your task is to remove the piece of paper without touching the water bottle.

Another water bottle activity Open the cap of the water and place an index card on top of the bottle. Place a skittle on top of the index card. Challenge: get the skittle into the water.

Thinking example #4 Watch the following video and describe what is happening based on the first law of motion. http: //www. youtube. com/watch? v=cu. G 8 s. Ii. V 8 i. Q

Why does it keep rolling? Observe a cart rolling along the floor. After we push it, why does it continue to roll? What force is keeping it going? ? NO FORCE keeps it going.

Thought experiment #5 Imagine you are in the back of your friend’s car with 2 other buddies and you are in the center. As the car turns to the right, which buddy will you squish? What is causing this to happen? (Describe using Newton’s 1 st Law)

Galileo’s version of the law Galileo knew Newton’s First Law well before Newton… However, Galileo was concerned with how things moved, not why they moved.

Thought Experiment Let’s look at the following picture and situation… (pg. 45 of textbook)

How do we measure inertia? Mass is the measure of inertia. Mass is NOT volume Consider a fluffy pillow vs. a shot put. Mass is not weight Consider the following demonstration… http: //www. youtube. com/watch? v=a. Cq. Qzr. PC c. FM

Units of mass Metric units are kilograms 1 kilogram is approximately the weight of a baseball bat or a medium sized pumpkin, or a high school discus. English units are slugs.

Calculating weight Weight = mass * acceleration due to gravity Acceleration due to gravity = 9. 8 m/s/s on Earth. Units for weight… Metric units are Newtons English Units are Pounds

Common misconception with Newton’s First law of motion An object that is motionless DOES NOT MEAN that there are no forces acting on the object. If an object is motionless or at a constant linear speed, it is said to be at EQUILIBRIUM. There is no net force on the object

Thought Examples A book on a table A person standing on the ground Normal force explained A traffic light hanging from wires in the middle of an intersection.