DAILY QUESTION

January 7, 2009

1. What is the definition of force?

Agenda 1/7/09

• Daily Question• Partner Check – Problems Wksht• Check-in: Problems Wksht• Chapter 10 – Motion• New Read Aloud! “Life As We Knew It”• Assignments:

1. Study for Quiz on 1/9

Force

• Anything that changes the state of rest or motion of an object

Net Force

• The combination of all of the forces acting on the object.– Balanced forces = net force of zero

• Do not cause a change in the motion of a moving object

– Unbalanced forces = net force is greater than zero

• Object will move in the direction of greater force

Friction

• A force that opposes motion between two surfaces that are in contact– Static friction: surfaces are stationary– Kinetic friction: surfaces are moving

Static friction is usually greater than kinetic friction.

Kinetic Friction

• Different kinds:– Sliding Friction: Object slide past each other– Rolling Friction: Round object rolls over flat

surface

Rolling friction is usually less than sliding friction.– Fluid Friction: Object moving through a fluid