# Forces / Friction Study Guide for Science Use for Mrs. Grom’s 8 th. Grade Science class.

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Forces / Friction Study Guide for Science Use for Mrs. Grom’s 8 th. Grade Science class

WHAT IS A FORCE? A FORCE is a push or a pull! A FORCE can set an object into motion. There are 2 types of forces – BALANCED and UNBALANCED OR A PULL! A PUSH

BALANCED FORCES These are forces that are EQUAL and in OPPOSITE DIRECTIONS DO NOT cause an object to go into motion and DO NOT cause an object to STOP motion already begun.

UNBALANCED FORCES! These forces are NOT EQUAL and IN THE SAME DIRECTION CAN CAUSE an object to START or STOP its motion sciencekit.com/category.

FRICTION A force which OPPOSES motion! OFTEN slows things down. THREE TYPES –SLIDING –ROLLING –FLUID

SLIDING FRICTION Occurs when something or someone SLIDES across a surface. LUBRICANTS like oil or grease HELP reduce sliding friction. LUBRICANTS change sliding friction to rolling friction. encarta.msn.com/media_

ROLLING FRICTION This friction involves the use of WHEELS, BALL BEARINGS, TIRES, etc. This friction tends to be less than sliding friction. (using wheels can make work easier)

FLUID FRICTION! This type of friction involves EITHER WATER or AIR! This type of friction opposes motion MUCH LESS than sliding friction does! LUBRICANTANTS are often used to CHANGE sliding friction into FLUID friction because it is LESS DAMAGING.

Inertia This is the TENDENCY of matter to RESIST CHANGE in motion. FOUND in places like – - amusement park rides - a car going around a curve - a car hitting its breaks hard The object WANTS to keep going in the direction the motion has started the object in like when you go forward as you hit the breaks.

Sir Isaac Newton (Not really necessary to know this for test – just interesting facts!) Birth - December 25, 1642 Death - March 20, 1727 Place of Birth - Woolsthorpe, England Known for: Inventing, in part, the branch of mathematics now known as calculus Formulating the three laws of motion, which describe classical mechanics Proposing the theory of universal gravitation, which explains that all bodies are affected by the force called gravity encarta.msn.com/media

Newton’s 1 st. Law of Motion STATES THAT – - An object at REST will REMAIN at rest and an object in MOTION will REMAIN in MOTION unless ACTED UPON by an outside force. The book will stay on the table until someone moves it! The tractor will stay in motion until the farmer hits the brakes.

Newton’s 2 nd. Law of Motion This law describes how FORCE, ACCELERATION and MASS are related. The formula for this is: Force = Mass X Acceleration or OR Which would require a greater force (in NEWTONS) to accelerate? /www.aloha.com/~isaac/3laws/2mid.htm FORCE is measured in NEWTONS!

Newton’s 3 rd. Law of Motion Newton’s THIRD law states that forces occur in PAIRS. IN OTHER WORDS: For EVERY action, there is an EQUAL and OPPOSITE reaction! ACTION – Stan punches Fred! REACTION – Fred’s head moves sideways and he yells “OUCH!” ACTION: The rocket engines “fire up” REACTION: The rocket lifts up off the launch pad and begins it’s journey into outer space. www.aloha.com/~isaac/3laws/3mid.htm

GRAVITY! Gravity causes objects to ACCELERATE at a rate of 9.8 m/sec/sec when they are close to the Earth’s surface. GRAVITY is a force that exists between ALL objects in the universe. Newton’s Law of Universal Gravitation states that ALL OBJECTS in the UNIVERSE attract each other by the force of gravity. The size of the force of gravity depends on TWO factors – 1.) the mass of the two objects 2.) the distance between them

WEIGHT AND MASS WEIGHT is the measure of the PULL of gravity on a given object (mass)

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