Thursday, Oct 23, 2008 - Block 1

Went around room asking student what they told their parents about the inertia labs.
Talked about the various labs and explained them in terms of inertia.

Handed back RA 4.1 and went over it.

Show demo of compressing spine and why you are taller in the morning.

A force is simply a push or a pull.

Explained what is meant by a net force - vector sum of all forces acting on an object.

Introduced Newton's First Law of Motion: If there is no net external force acting on an object, an object at rest remains at rest and an object in motion keeps moving in a straight line with constant speed.

"Straight line with constant speed" means constant velocity.

Constant velocity means NO NET FORCE.

Mass, measured in kg, is a measure of inertia. If you toss an object back and forth from hand to hand you are measuring its inertia, how hard or easy it is to change its state of motion.

Volume and weight are NOT the same as mass.

Weight, measured in Newtons, is the force of gravity on an object. If you hold an object in your hand, you are measuring its weight.

A mass of 1 kg weights 10 N at the surface of the Earth. (Show with mass and spring balance.)

A mass of 1 kg also weighs about 2.2 lbs on Earth. One Newton is about the same as 0.22 lbs (A mass of 1 kg weighs 2.2 lbs) 0.22 lbs ~ 0.25 lbs. Therefore, instead of ordering a quarter pounder, you could order a Newtonburger.

Normal is a mathematical term meaning perpendicular to a surface. A normal force, which you have only with a surface (NOT strings) is the force perpendicular to that surface. Do NOT just include a normal force in all problems. There has to be a surface.

Introduced the idea of free-body diagrams. Isolate an object and show only the external forces that act on that object. You do NOT show velocity vectors, etc. or any forces that that object exerts on something else. Did a few examples of drawing free body diagrams.

Homework sheet Newton's Laws worksheet.