1. Forces 10.27.09 8 th Grade Physical Science Ms. McKinley

2.  What is a Force?  a Force is a push or pull.  2 categories : contact and non-contact  Contact Force  exerted when two objects are touching.  Non-contact Force  exerted on one object by another when the objects are NOT touching.

3.  Combining Forces  When 1 or more forces acts on an object, the forces combine.  The NET FORCE is the combo of ALL forces acting on an object.  When net force = 0, forces are BALANCED.  The object does not move. Velocity doesn’t change  When net force ≠ 0, forces are UNBALANCED.  The velocity of the object changes

4.  Types of Forces: Gravity  An attractive force between all objects that have mass.  Mass: the amount of matter in an object. Weight: the pull of gravity on an object. ALWAYS points toward the center of the Earth.

5. Quick check: Which object has more mass? Caterpillar Gorilla You guessed it! The Gorilla has more mass than the caterpillar

6.  Types of Forces: Gravity  An attractive force between all objects that have mass.  Mass: the amount of matter in an object.  Gravitational force (gravity) gets stronger as either or both objects increase in mass.  Earth’s gravitational force is HUGE because the Earth is HUGE!  So Earth pulls you towards itself

7.  Types of Forces: Friction  A force that resists sliding between two touching surfaces  Friction ALWAYS works opposite the direction of motion.

8.  Types of Forces: Tension  A pulling force exerted on an object when it is stretched.  When you pull a rubber band, it stretches. This is tension!

9.  Types of Forces: Compression  A squeezing force applied to an object that can make an object shrink

10.  Types of Forces: Normal  Force exerted by an object that is perpendicular to the surface of the object. The NORMAL FORCE keeps this glass from shooting through the table. The NORMAL FORCE is keeping this boy from falling through the chair!

11.  Standard 2f