CHAPTER 19-NEWTON’S FIRST LAW

8TH GRADE

INTRODUCTION

PGS. 550-552

DO NOW…

• WRITE AGREE OR DISAGREE FOR THE FOLLOWING STATEMENTS.

Agree or Disagree

Statement

A force is a push or pull.

Objects must be touching each other to apply forces on one another. Gravity pulls on all objects that have mass.

An object traveling in a circle at a constant speed is not accelerating.

OBJECTIVES

STUDENTS WILL…

• DISTINGUISH BETWEEN BALANCED AND NET FORCES

• DESCRIBE NEWTON’S FIRST LAW OF MOTION

FORCES ON A BOOK

• IF A BOOK WERE PUSHED ACROSS A TABLE….

•WHAT IS THE MOTION OF THE BOOK?

• IN THIS CHAPTER, YOU WILL LEARN TO DESCRIBE THE MOTION OF THE BOOK IN TERMS OF THE FORCES ACTING UPON IT AND ACCORDING TO NEWTON’S FIRST LAW OF MOTION.

HAVE YOU EVER THOUGHT….?

•AN OBJECT AT REST RESISTS ACCELERATION ONLY BECAUSE OF FRICTION. TRUE OR FALSE?

•HAS ANYONE EVER HELPED TO PUSH A STALLED CAR?

•DID YOU NOTICE THAT IT TAKES A LOT OF EFFORT TO GET THE CAR GOING AND LESS EFFORT TO KEEP IT GOING?

•WHY DOES IT TAKE A LARGER FORCE TO MOVE A STOPPED CAR THAN IT DOES IT PUSH A MOVING CAR?

FORCE

• A FORCE IS A PUSH OR PULL.

• EXAMPLES: GOLF CLUB ON A GOLF BALL, THE MAGNET ON A CRANE PULLING PIECES OF SCRAP METAL UPWARD

•WHAT IS FORCE?

•WHAT FORCES ARE ACTING ON YOU?

COMBINING FORCES

• MORE THAN ONE FORCE AN ACT ON AN OBJECT AT THE SAME TIME AND THE COMBINATION OF THESE FORCES ACTING ON AN OBJECT IS THE NET FORCE.

HOW FORCES COMBINE TO FORM A NET FORCE

•2 IMPORTANT THINGS TO REMEMBER

1) IF FORCES ACT IN THE SAME DIRECTION, THE FORCES ADD TOGETHER.

2) IF THE FORCES ACT IN OPPOSITE DIRECTIONS, THE NET FORCE IS THE DIFFERENCE BETWEEN THE FORCES.

BALANCED AND UNBALANCED FORCES

• A FORCE CAN ACT ON AN OBJECT WITHOUT CAUSING IT TO ACCELERATE IF OTHER FORCES CANCEL THE PUSH OR PULL OF THE FORCE.

BALANCED FORCES

- 2 OR MORE FORCES EXERTED ON AN OBJECT ARE BALANCED IF THEIR EFFECTS CANCEL EACH OTHER AND THEY DO CHANGE THE OBJECT’S VELOCITY. IF THE FORCES ARE BALANCED, THEN THE NET FORCE IS ZERO.

UNBALANCED FORCES

-IF THE NET FORCE IS NOT ZERO, THE FORCES ARE UNBALANCED. THEN THE EFFECTS OF THE FORCES DON’T CANCEL AND THE OBJECT’S VELOCITY CHANGES.

NEWTON’S FIRST LAW OF MOTION• WHAT CAN YOU TELL ME ABOUT SIR ISAAC NEWTON?

• SIR ISAAC NEWTON

NEWTON’S FIRST LAW OF MOTION

• STATES THAT IF AN OBJECT IS AT REST AND THE NET FORCE IS ZERO, IT WILL STAY AT REST. IF IT IS ALREADY MOVING AND THE NET FORCE ON IT IS ZERO, IT WILL CONTINUE TO MOVE IN A STRAIGHT LINE WITH A CONSTANT SPEED.

• FIRST LAW OF MOTION

FOR REVIEW…

•WHAT IS THE DIFFERENCE BETWEEN A BALANCED AND AN UNBALANCED FORCE?

FOR NEXT TIME…

•TEST SIGNED BY A PARENT DUE THURSDAY, 10/24

•READ PGS. 553-555 (PLEASE MAKE SURE YOU READ!)

•DEFINE NEWTON’S FIRST LAW OF MOTION AND FRICTION.

TYPES OF FRICTION8TH GRADE

MINI LAB-OBSERVING FRICTION

REVIEW AND PREVIEW…..

WITH YOUR LAB GROUP, ANSWER THE QUESTION ON THE INDEX CARD. BE PREPARED TO SHARE YOUR ANSWER WITH THE REST OF THE CLASS.

OBJECTIVES

STUDENTS WILL…

CREATE A FOLDABLE TO EXPLORE THE THREE DIFFERENT TYPES OF FRICTION

COMPLETE A MINI LAB TO OBSERVE FRICTION IN ACTION

FRICTION FOLDABLE

• A DIFFERENT WAY OF TAKING NOTES AND ORGANIZING INFORMATION

• SET UP FOLDABLE ACCORDING TO TEACHER INSTRUCTIONS

• HEADING: TYPES OF FRICTION AND DEFINITION OF FRICTION ON FLIP SIDE

• THREE TABS FOR TYPES OF FRICTION—LABELED AS WE GO ALONG

• QUESTIONS/CONFUSION?

FRICTION AND NEWTON’S FIRST LAW

• FRICTION IS THE FORCE THAT BRINGS NEARLY EVERYTHING TO A STOP. IT ACTS TO RESIST SLIDING BETWEEN TWO TOUCHING SURFACES.

•HOW ARE FRICTION AND NEWTON’S FIRST LAW RELATED?

•NEWTON’S FIRST LAW STATES: IF THE NET FORCE ACTING ON AN OBJECT IS ZERO, THE OBJECT REMAINS AT REST. IF THE OBJECT IS ALREADY MOVING, IT CONTINUES TO MOVE IN A STRAIGHT LINE WITH CONSTANT SPEED.

FRICTION AND NEWTON’S FIRST LAW

•FRICTION FOLLOWS NEWTON’S FIRST LAW. (IT DOES NOT CHANGE IT!)

•IT ACTS UPON AN OBJECT IN MOTION THEREFORE TRYING TO BRING IT TO A STOP.

•IT ALSO HELPS OBJECTS AT REST STAY AT REST.

TYPES OF FRICTION

STATIC FRICTION•PREVENTS AN OBJECT FROM MOVING WHEN A FORCE IS APPLIED TO IT

•THINK “STATIONARY OR STILL”

•EXAMPLES:

•A BACKPACK SITTING IN THE MIDDLE OF THE HALLWAY, A VASE RESTING ON A TABLETOP

TYPES OF FRICTION

SLIDING FRICTION• SLOWS DOWN A SLIDING OBJECT

• ACTS IN THE DIRECTION OPPOSITE OF A MOTION TO SLOW SOMETHING DOWN

• THINK “SLOWING”

• EXAMPLES:

• A BASEBALL PLAYER SLIDING INTO HOME BASE, A CHAIR THAT WAS PUSHED SLOWING DOWN AND STOPPING IN THE MIDDLE OF A ROOM

TYPES OF FRICTION

ROLLING FRICTION• A FORCE THAT MAKES A CIRCULAR SHAPE/WHEEL TURN

• FRICTION BETWEEN THE ROLLING OBJECT AND THE SURFACE ON WHICH IT IS ROLLING

• THINK “WHEELS”

• EXAMPLES:

• A SCOOTER MOVING DOWN THE STREET, A STROLLER BEING PUSHED DOWN A SIDEWALK

EXAMPLES OF FRICTION

•WOODEN SURFACE

• 3 OBJECTS: SHOE, TOY WITH WHEELS, PIECE OF METAL

• PREDICT: WHICH OBJECT WILL SLIDE THE FASTEST/SLOWEST? (WHY?)

•WHICH OBJECT WILL HAVE THE GREATEST/LEAST AMOUNT OF FRICTION? (WHY?)

•OTHER EXAMPLES OF FRICTION IN THE CLASSROOM OR AROUND THE SCHOOL.

MINI LAB: OBSERVING FRICTION

•PURPOSE: STUDENTS WILL OBSERVE THE STATIC AND SLIDING FRICTION BETWEEN VARIOUS OBJECTS.

•LAB PROCEDURES/DIRECTIONS/SAFETY PRECAUTIONS

•COMPLETE LAB WORKSHEET—DON’T FORGET TO EXPLAIN WHY!

FOR REVIEW…

• DEFINE AND IDENTIFY THE TYPE OF FRICTION IN EACH OF THE FOLLOWING SITUATIONS.

• 1) A BICYCLE TIRE ROLLING ALONG THE ROAD

• 2) A BOX RESTING ON A RAMP

• 3) AN TEXTBOOK BEING PUSHED ACROSS A TABLE AND COMING TO A STOP

• FOR NEXT TIME…

• FINISH LAB WORKSHEET IF NEEDED

• READ PAGES 556-559

• DEFINE NEWTON’S SECOND LAW AND WEIGHT ON INDEX CARDS