Name: _______________________________ Class: ____Name: _______________________________ Class: ____

12.212.2 Newton’s 1st & 2nd Laws of Motion Newton’s 1st & 2nd Laws of Motion

Chapter 12Chapter 12Forces and MotionForces and Motion

What are we going to learn?What are we going to learn?

Newton’s Laws of MotionNewton’s Laws of Motion(Imagine a toy car with an unanchored load (Imagine a toy car with an unanchored load

– what will change its motion?)– what will change its motion?)

What is a Scientific Law?What is a Scientific Law?A A statementstatement of what will of what will happenhappen in a given set in a given set of of circumstancescircumstances..

FYI: FYI: NewtonNewton developed the developed the Law of UniversalLaw of Universal GravitationGravitation in addition to the Laws of Motion in addition to the Laws of Motion

Newton’s First Law of MotionNewton’s First Law of MotionAn An object at restobject at rest will will remain at restremain at rest unless unless acted uponacted upon by a by a nonzero net force nonzero net force An An object movingobject moving at a at a constant velocityconstant velocity will will continue movingcontinue moving at a constant velocity at a constant velocity unlessunless acted upon by a acted upon by a nonzero net forcenonzero net force

InertiaInertiaTThe he tendencytendency of an object ( of an object (moving or notmoving or not) to ) to resist a changeresist a change in its motion in its motionNewton’s 1Newton’s 1stst Law is also known as the Law is also known as the Law ofLaw of InertiaInertiaEx: You Ex: You move forwardmove forward in your seat in your seat whenwhen your your car stopscar stops suddenly suddenlyRelate inertia to safety bars on a roller coasterRelate inertia to safety bars on a roller coaster

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InertiaInertiaRelate inertia to safety bars on a roller coasterRelate inertia to safety bars on a roller coaster

They keep you in your seat when changes in the They keep you in your seat when changes in the coaster’s motion moves you out of your seatcoaster’s motion moves you out of your seat

Mass and InertiaMass and Inertia

The The greater the massgreater the mass of an object, the of an object, the greater greater its its inertiainertia...and the ...and the greater the forcegreater the force required to required to change its motionchange its motion

Use this information to explain why you feel Use this information to explain why you feel tossed around whenever a roller coaster goes tossed around whenever a roller coaster goes over a hill or through a loop...over a hill or through a loop...

Use this information to explain why you feel Use this information to explain why you feel tossed around whenever a roller coaster goes tossed around whenever a roller coaster goes over a hill or through a loopover a hill or through a loopBecause of inertia, you resist changes in Because of inertia, you resist changes in motion. When the coaster accelerates over a motion. When the coaster accelerates over a hill, inertia keeps you moving at a constant hill, inertia keeps you moving at a constant velocity. You feel tossed velocity. You feel tossed around.around.

ExampleExampleWhat keeps a ball rolling down a hill?What keeps a ball rolling down a hill?

ExampleExampleWhat keeps a ball rolling down a hill?What keeps a ball rolling down a hill?Gravity and InertiaGravity and Inertia

What force is acting on the ball, resisting What force is acting on the ball, resisting motion?motion?

What force is acting on the ball, resisting What force is acting on the ball, resisting motion?motion?Friction between the ball and the groundFriction between the ball and the ground

If you put a ball on the floor and roll it across If you put a ball on the floor and roll it across the floor so it hits the wall, why did the ball the floor so it hits the wall, why did the ball stop moving in the direction it was rolled?stop moving in the direction it was rolled?

If you put a ball on the floor and roll it across If you put a ball on the floor and roll it across the floor so it hits the wall, why did the ball the floor so it hits the wall, why did the ball stop moving in the direction it was rolled?stop moving in the direction it was rolled?It rolled into the wall, so it could not keep It rolled into the wall, so it could not keep going in the direction it was rolledgoing in the direction it was rolled

Now I get it!Now I get it!Now I know that Newton’s first law of motion Now I know that Newton’s first law of motion states that _____________________________states that _____________________________

Now I get it!Now I get it!Now I know that Newton’s first law of motion Now I know that Newton’s first law of motion states that states that objects only change motion when a objects only change motion when a nonzero net force acts on themnonzero net force acts on them

Newton’s Second Law of MotionNewton’s Second Law of MotionAn object’s An object’s accelerationacceleration depends on its depends on its massmass and on the and on the net forcenet force acting on it acting on itEx: Is a full or empty shopping cart easier to Ex: Is a full or empty shopping cart easier to push?push?Ex: Who can cause a greater acceleration on Ex: Who can cause a greater acceleration on the cart, a small child or grown adult?the cart, a small child or grown adult?

Newton’s Second Law of MotionNewton’s Second Law of MotionEx: Is a full or empty shopping cart easier to Ex: Is a full or empty shopping cart easier to push? push? Empty cart – less massEmpty cart – less massEx: Who can cause a greater acceleration on Ex: Who can cause a greater acceleration on the cart, a small child or grown adult? the cart, a small child or grown adult? Grown Grown adult – more forceadult – more force

FormulaFormulaThe The accelerationacceleration of an object is of an object is equal toequal to the the net forcenet force acting on it acting on it divided bydivided by the object’s the object’s massmass Acceleration = Acceleration = Net forceNet force

MassMass oror

Net force = Mass x AccelerationNet force = Mass x Acceleration

Mass x Acceleration = Mass x Acceleration = Net forceNet force x Mass x Mass MassMass which giveswhich gives

Mass x Acceleration = Net forceMass x Acceleration = Net force

when flipped giveswhen flipped gives

Net force = Mass x AccelerationNet force = Mass x Acceleration

Changes in Force and MassChanges in Force and MassIf you If you increase the forceincrease the force on a cart without on a cart without changing its mass, the changing its mass, the accelerationacceleration will will increaseincreaseIf something falls out (If something falls out (decrease massdecrease mass), it will ), it will accelerate fasteraccelerate faster if you keep pushing just as if you keep pushing just as hard (same hard (same forceforce))

If you want to increase the acceleration of a If you want to increase the acceleration of a bicycle, what must you increase?bicycle, what must you increase?

If you want to increase the acceleration of a If you want to increase the acceleration of a bicycle, what must you increase?bicycle, what must you increase?The force you apply to the pedalsThe force you apply to the pedals

Why are racing bicycles made of lightweight Why are racing bicycles made of lightweight metals like titanium?metals like titanium?

Why are racing bicycles made of lightweight Why are racing bicycles made of lightweight metals like titanium?metals like titanium?The less mass a bicycle has, the greater the The less mass a bicycle has, the greater the acceleration the rider can produceacceleration the rider can produce

Suppose 4 dogs pull a sled carrying 2 people. Suppose 4 dogs pull a sled carrying 2 people. Change the dog/person arrangement to change Change the dog/person arrangement to change the sled’s acceleration in the 2 questions.the sled’s acceleration in the 2 questions.

Suppose 4 dogs pull a sled carrying 2 people. Suppose 4 dogs pull a sled carrying 2 people. Change the dog/person arrangement to change Change the dog/person arrangement to change the sled’s acceleration in the 2 questions.the sled’s acceleration in the 2 questions.

Which part of the formula would you change if Which part of the formula would you change if you added dogs to the team?you added dogs to the team?

Which part of the formula would you change if Which part of the formula would you change if you added dogs to the team?you added dogs to the team?Net forceNet force

How does changing the How does changing the toptop number of a number of a fraction affect the value of the answer?fraction affect the value of the answer?

How does changing the How does changing the toptop number of a number of a fraction affect the value of the answer?fraction affect the value of the answer?It increases the valueIt increases the value

Write an “if-then” sentence to show the effect of Write an “if-then” sentence to show the effect of adding more dogsadding more dogs

Write an “if-then” sentence to show the effect of Write an “if-then” sentence to show the effect of adding more dogsadding more dogsIfIf you add dogs to the team, you add dogs to the team, thenthen you increase you increase the accelerationthe acceleration

What else could be done to increase What else could be done to increase acceleration?acceleration?

What else could be done to increase What else could be done to increase acceleration?acceleration?By removing some people from the sled or a By removing some people from the sled or a combination of adding dogs and removing combination of adding dogs and removing peoplepeople

Remember:Remember:Mass units are kgMass units are kgAcceleration units are m/sAcceleration units are m/s22

Force units are N (kg · m/sForce units are N (kg · m/s22))

Force = Mass x Acceleration

2 kg x 2 m/s2 = 4N

It would be cut in half to become 1 m/s2

I get it! I get it! Now I know that Newton’s second law Now I know that Newton’s second law of motion describes the relationship ________of motion describes the relationship ________

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I get it! I get it! Now I know that Newton’s second law Now I know that Newton’s second law of motion describes the relationship of motion describes the relationship among among force, mass and accelerationforce, mass and acceleration