Download Newton*s third Law of Motion

NEWTON’S THIRD LAW OF
MOTION
8TH GRADE
PGS. 563-583
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 3RD 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 3rd Law
Action force
Rocket fuel is
ignited, producing The walls of the
hot gas.
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
Weightlessness
Causes a sensation of: Not
Having Weight
Happens in spacecraft
because: objects that orbit
earth are in free fall
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.