NEWTON’S THIRD LAW OF MOTION 8 TH GRADE PGS

TALK ABOUT IT… WITH YOUR LAB GROUP/SEAT PARTNERS WHAT IS THE FORCE EXERTED ON YOU BY YOUR CHAIR? DOES YOUR BODY IN RETURN ALSO EXERT A FORCE BACK ON THE CHAIR? ANSWER: THE FORCE OF THE CHAIR PUSHING YOU UP IS COUNTER ACTED BY THE FORCE OF GRAVITY WHICH IS PULLING YOU BACK DOWN. ACCORDING TO NEWTON’S 3 RD LAW, ALL FORCES ACT IN PAIRS.

OBJECTIVES STUDENTS WILL IDENTIFY THE RELATIONSHIP BETWEEN THE FORCES THAT OBJECTS EXERT ON EACH OTHER.

FROM THE OTHER DAY… MISCONCEPTIONS ABOUT FALLING OBJECTS

ACTION AND REACTION NEWTON’S THIRD LAW OF MOTION -FORCES ALWAYS ACT IN EQUAL BUT OPPOSITE PAIRS. - FOR EVERY ACTION, THERE IS AN EQUAL REACTION. NEWTON’S THIRD LAW OF MOTION NEWTON’S THIRD LAW OF MOTION DEMONSTRATION

ACTION AND REACTION FORCES DON’T CANCEL THE FORCES EXERTED BY 2 OBJECTS ON EACH OTHER ARE CALLED AN ACTION AND REACTION FORCE PAIR. EITHER FORCE CAN BE CONSIDERED THE ACTION OR REACTION FORCE. THEY DO NOT CANCEL EACH OTHER IF THEY ACT ON DIFFERENT OBJECTS. FORCES CAN CANCEL ONLY IF THEY AT ON THE SAME OBJECT. DRAW A PICTURE OF AN ACTION-REACTION FORCE (USE ARROWS TO LABEL THE FORCES) EXAMPLE: BUMPER CARS, JUMPING OFF OF SOMETHING, A BIRD FLYING

ONE MORE THING A CHANGE IN MOTION DEPENDS ON MASS SOMETIMES YOU MIGHT NOT NOTICE THE EFFECTS OF THE FORCES IN AN ACTION/REACTION PAIR. THIS CAN HAPPEN IF ONE OF THE OBJECTS INVOLVED IS MUCH MORE MASSIVE THAN THE OTHER. THIS IS WHY THE MASSIVE OBJECT MIGHT SEEM TO REMAIN MOTIONLESS. EXAMPLE: A PERSON WALKING ON THE GROUND. (GROUND/EARTH IS MASSIVE=MOTION IS UNDETECTED)

ROCKET LAUNCH Newton’s 3 rd Law Rocket fuel is ignited, producing hot gas. Action force The walls of the engine exert a force that pushes gas molecules out and down. Reaction force The gas molecules push the rocket engine upward.

Occurs during: Free Fall Happens because: gravity is the only force acting on an object Causes a sensation of: Not Having Weight Happens in spacecraft because: objects that orbit earth are in free fall Weightlessness

FOR NEXT TIME… THE PHYSICS OF SKY DIVING WATCH NEWTON’S THIRD LAW AND TAKE QUIZ ON NEWTON’S THIRD LAW OF MOTION ON KHAN ACADEMY.