Oct. 8 – Newton's First Law and Inertia

I couldn't be in class yesterday due to a field trip for another class.  Here are the handouts I left with the supply teacher:

• Free Body Diagrams 2
• Free Body Diagrams Worksheet

Here are the solutions to the worksheet:

More on Newton's 1st Law (Inertia)

Inertia

• The tendency for an object to keep moving (or stay motionless).
• Inertia is directly related to mass.  More mass means more inertia.

There were two space probes launched in 1977 called Voyager 1 and Voyager 2.  They have no rockets and no source of propulsion on board.  They are now over 18 billion km away.  Here's a tracker from NASA http://voyager.jpl.nasa.gov/where/

•        What will happen to them?

Since there is no forces acting on them, they will keep going due to Newton's First Law.

• An object in motion tends to stay in motion unless acted upon by an external force.

In fact, they will keep going forever unless they encounter something to exert a force on them.  In the space between our sun and other starts, there's really not much that will stop them!

Here's an image taken by Voyager:

The tiny speck in the beam on the right is the Earth!

Here's what Carl Sagan had to say about this image:

From this distant vantage point, the Earth might not seem of any particular interest. But for us, it's different. Consider again that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every corrupt politician, every "superstar," every "supreme leader," every saint and sinner in the history of our species lived there – on a mote of dust suspended in a sunbeam.

—Carl Sagan, Pale Blue Dot: A Vision of the Human Future in Space, 1997 reprint, pp. xv–xvi

On Earth, we also see Newton's First Law in action all the time:

A force from the tires stops the bike, but this force doesn't act on the rider, so he keeps going!

The same is true for cars.  If there's not enough friction to stop a car, say on an icy road for instance, cars will have a difficult time stopping:

Using inertia, can you explain how this works?

Possible solution:

When the card is flicked, a force acts on the card.  No addition force is applied to the coin (small bit of friction), therefore, due to inertia, the coin remains motionless.  Once the card is removed, there is no longer a normal force on the coin, the net force is gravity, causing the coin to fall into the cup.

Homework

• You can now do the homework from Day 1 and Day 2 of the unit plan.