Tuesday, Oct 26, 2010

Review what students told parents about inertia mini-labs
Review inertia mini lab results

Newton's First Law of Motion: An object at rest will stay at rest and an object in motion will continue moving in a straight line with constant speed unless acted on by an outside net force.

Net force - direction matters so we can't just add forces up as numbers, we have to consider direction. Quantities with both a how much and a which way are called vectors.

Free-body Diagrams: pictures showing only the FORCES that act ON an object

Adding Forces

If Fnet = 0, object is in equilibrium. Object at rest will stay at rest, object in motion will continue moving in a straight line with constant speed.

If Fnet not equal to zero, the object will change its motion, alteration of motion, called acceleration. Velocity is how fast and in what direction. You can change velocity by changing speed, direction, or both.

Acceleration = change in velocity/time
acceleration is a very difficult topic since it is the rate of a rate. Students often confuse velocity and acceleration, and often get the units mixed up. Example with money. Accelerations are caused by forces. As long as the net force acts, the object will accelerate, even if it is momentarily at rest.

Demo of Picket Fence Lab. Got acceleration of gravity to be about 10 m/s/s

Stopped class early - forgot it was an access schedule.

We have previously dealt with graphs of distance vs time. Often it is more useful to deal with velocity vs time graphs, especially when dealing with objects that are accelerating.

Compare the two graphs:
Object at rest
Object moving with constant speed
Object moving with changing speed

Example: throw an object up into the air.

You can "feel" acceleration due to inertia. (speeding up, slowing down, changing direction. Examples with car, as previously shown with Carly.