Come on PeopleCome on People

This is not rocket This is not rocket sciencescience

Oh, WaitOh, Wait

Yes it is!Yes it is!

Newtons First LawNewtons First Law

Chapter 6Chapter 6

Section 2Section 2

Thursday, April 20, 2023Thursday, April 20, 2023

ForceForce

An objects movement changes in An objects movement changes in response to a forceresponse to a force

A force is a push or a pullA force is a push or a pull Can be a contact forceCan be a contact force

• A push or a pullA push or a pull Can be a long range forceCan be a long range force

• GravityGravity• MagnetismMagnetism

Newton's First Law of MotionNewton's First Law of Motion

An object at rest stays at rest unless An object at rest stays at rest unless acted on by an outside forceacted on by an outside force

An object in motion stays in motion An object in motion stays in motion unless acted on by an outside forceunless acted on by an outside force

ForceForce

SI unit for force is the Newton (N)SI unit for force is the Newton (N) About the force needed to lift 4 About the force needed to lift 4

ounces of waterounces of water

Newtons First LawNewtons First Law

An object in motion tends to stay in An object in motion tends to stay in motion unless acted on by an outside motion unless acted on by an outside force.force.

An object at rest tends to stay at rest An object at rest tends to stay at rest unless acted on by an outside force.unless acted on by an outside force.

Also known as inertiaAlso known as inertia

Inertia and MassInertia and Mass

The more mass an object has the more The more mass an object has the more inertia it hasinertia it has

The more inertia an object has, the The more inertia an object has, the harder it is to change its motion. harder it is to change its motion.

So lets look at Football PhysicsSo lets look at Football Physics

Which would be better as a football Which would be better as a football lineman?lineman?

Why?

Adding ForcesAdding Forces

The motion of an object changes only The motion of an object changes only if a force is acting on itif a force is acting on it

More than one force can act on an More than one force can act on an objectobject

If forces act in opposite directions If forces act in opposite directions with equal force, no motion happenswith equal force, no motion happens

Balanced ForcesBalanced Forces

Adding ForcesAdding Forces

If one force is greater than the other If one force is greater than the other the object will move in the direction the object will move in the direction of the larger forceof the larger force

Motion only changes if forces are Motion only changes if forces are unbalancedunbalanced

Motion changes in the direction of Motion changes in the direction of the greater forcethe greater force

Newton’s Second LawNewton’s Second Law

Chapter 6Chapter 6

Section 3Section 3

The Second Law of MotionThe Second Law of Motion

Used to predict MotionUsed to predict Motion An object acted on by an unbalanced An object acted on by an unbalanced

force will accelerate in the direction force will accelerate in the direction of the forceof the force

This law is actually a formulaThis law is actually a formula

The Second Law of MotionThe Second Law of Motion

Acceleration = Force / Mass

Force = Mass x Acceleration

Or

OrOr

F=MAF=MA

Force MeasuredForce Measured

The SI Unit for Force is the NewtonThe SI Unit for Force is the Newton One Newton of Force will cause 1 kg One Newton of Force will cause 1 kg

of Mass to Accelerate at 1M/Sof Mass to Accelerate at 1M/S22

So 1N = 1M/SSo 1N = 1M/S22/kg/kg

Sample ProblemSample Problem

A child has a mass of 71kgA child has a mass of 71kg Her Bike has a mass of 9 kgHer Bike has a mass of 9 kg They accelerated at a rate of 3.2M/SThey accelerated at a rate of 3.2M/S2 2

How much force was applied?How much force was applied? Well, force equals mass times Well, force equals mass times

accelerationacceleration So F = 80kg x 3.2M/SSo F = 80kg x 3.2M/S22 = 256 kg/M/S = 256 kg/M/S22

Or 256NOr 256N

Force of GravityForce of Gravity

Gravity is a forceGravity is a force The force of Earth’s gravity causes all The force of Earth’s gravity causes all

objects to accelerate at the same objects to accelerate at the same rate when fallingrate when falling

The rate is 9.8M/SThe rate is 9.8M/S22

NASCAR PhysicsNASCAR Physics

“Physics is good stuff”

What in the wide, wide world of sports has What in the wide, wide world of sports has this stuff got to do with racing???this stuff got to do with racing???

Well…..Well…..

In scientific terms acceleration and In scientific terms acceleration and mass are inversely related.mass are inversely related.

If the force is the same (Like say If the force is the same (Like say from the engine)from the engine)

The more mass you have, the less The more mass you have, the less acceleration you get acceleration you get

Or the heavier the car, the slower the Or the heavier the car, the slower the acceleration given the same amount acceleration given the same amount of horsepowerof horsepower

So, which would be better as a So, which would be better as a racecar driver?racecar driver?

Why?

That was heavy!That was heavy!

Speaking of heavy Speaking of heavy That leads us to weightThat leads us to weight So wait around for the next So wait around for the next

fascinating factfascinating fact

The Bigger They Are The Harder The Bigger They Are The Harder They Fall (But Not Faster)They Fall (But Not Faster)

Weight = Mass X Acceleration due to Weight = Mass X Acceleration due to Gravity.Gravity.

So…So… If your mass is 60kgIf your mass is 60kg 60kg x 9.8 M/S60kg x 9.8 M/S22 = 588N = 588N In science, weight is expressed as In science, weight is expressed as

NewtonsNewtons

Silly Scientists!Silly Scientists!

Say What???Say What???

Because weight is the force caused Because weight is the force caused by gravity acting on mass.by gravity acting on mass.

The same force is acting on you The same force is acting on you whether you are falling or standing whether you are falling or standing on the ground.on the ground.

Mass and WeightMass and Weight

In common language mass and In common language mass and weight are spoken of as the same weight are spoken of as the same thing.thing.

In zero gravity you have no weight In zero gravity you have no weight (that’s why we call it weightless)(that’s why we call it weightless)

But you have the same mass.But you have the same mass. On the moon, you would have about On the moon, you would have about

1/61/6thth of you earth weight but the of you earth weight but the same masssame mass

A balance is used for measuring mass because a balance compares an object's mass to a set of standard masses

A spring scale is used for measuring weight because a spring scale measures the force of gravity pulling objects downward.

1kg of bananas weighs 9.8N on Earth.

1 kg of bananas have a mass of 1.0 kg on Earth.

1kg of bananas weighs 3.7N on Mars.

1 kg of bananas have a mass of 1.0kg on Mars (even if they're Martian bananas)

Football PhysicsFootball Physics

Would the Would the advantage be the advantage be the same on the same on the moon?moon?

Yes, the mass is Yes, the mass is the same, the force the same, the force is caused by mass is caused by mass not weight.not weight.

FrictionFriction

A force that resists motionA force that resists motion But is essential to our livesBut is essential to our lives Could you get here without frictionCould you get here without friction NoNo Why?Why?

Without Friction…Without Friction…

Moving is a bear

Three Types of FrictionThree Types of Friction

Static FrictionStatic Friction

Why does the food Why does the food not slide off the not slide off the tray when the tray when the waiter starts or waiter starts or stops?stops?

Static friction Static friction resists movement resists movement relative to the tray.relative to the tray.

Sliding Friction Sliding Friction

Will the glass make it?

What will slow it down?

What will make it slide better?

Rolling FrictionRolling Friction

Air ResistanceAir Resistance