Section 2.1Section 2.1

Newton’s First Law of MotionNewton’s First Law of Motion

Newton: Great Scientist or Newton: Great Scientist or 80’s Rock Star?80’s Rock Star?

English Physicist English Physicist /Mathematician/Mathematician

1642-17271642-1727 Invented Calculus Invented Calculus

to explain what he to explain what he observedobserved

Discovered 3 Discovered 3 LAWSLAWS OF MOTIONOF MOTION

Use the Force, Luke…but only Use the Force, Luke…but only if you know what it is!if you know what it is!

A A force force is a is a push push or or pullpull, or , or any any action that has the ability to change action that has the ability to change motion.motion.

Where is the force in these Where is the force in these examples?examples?ActionAction What caused the What caused the

force?force?

Person lifts a boxPerson lifts a box

Gun fires bulletGun fires bullet

Branch falls from Branch falls from treetree

Nothing can start or stop Nothing can start or stop moving unless a force is moving unless a force is

applied!applied!

O RLY?!?O RLY?!?

YEAH RLY!YEAH RLY!

?Question??Question?

Can there be a change in the motion Can there be a change in the motion of anything without a force being of anything without a force being applied?applied?

NO!NO!

Okay smarty, I think you got it!Okay smarty, I think you got it!

Newton’s First LawNewton’s First Law

An object at rest will stay at rest and An object at rest will stay at rest and an object in motion will continue in an object in motion will continue in motion with the same speed and motion with the same speed and direction UNLESS acted on by a direction UNLESS acted on by a

force.force.

?Question??Question?

So a space ship is going 75,000 m/sSo a space ship is going 75,000 m/s

(or 75 km/s). It takes a left turn at (or 75 km/s). It takes a left turn at Pluto, but never changes speed. Was Pluto, but never changes speed. Was there a force acting on it??there a force acting on it??

Yes!Yes!

In order to change direction,In order to change direction,

A force A force mustmust be applied! be applied!

Which would you rather do?Which would you rather do?

Lift (move) a bag Lift (move) a bag with groceries in itwith groceries in it

Lift (move) a semi-Lift (move) a semi-trucktruck

Easy choice, rightEasy choice, right

It is much easier to lift the groceries It is much easier to lift the groceries and possibly impossible (for you and possibly impossible (for you weaklings, anyway) to lift the truck.weaklings, anyway) to lift the truck.

Why is one harder to move than the Why is one harder to move than the other?other?

MassMass

You remember mass…it’s the You remember mass…it’s the measure of how much matter an measure of how much matter an object has.object has.

It turns out, the more mass It turns out, the more mass something has, the more force is something has, the more force is required to move it.required to move it.

Duh!Duh!

InertiaInertia

Inertia is the property of objects to Inertia is the property of objects to resist changes in motion.resist changes in motion.

If something is stationary, it resists If something is stationary, it resists attempts to move itattempts to move it

If something is moving, it resists If something is moving, it resists attempts to slow it down (or speed it attempts to slow it down (or speed it up)up)

The more mass something has, the The more mass something has, the more inertia it has, and this means more inertia it has, and this means that more force is required to that more force is required to increase or decrease its speed.increase or decrease its speed.

Which would you rather do?Which would you rather do?Part 2Part 2

Stop a bag of Stop a bag of groceries that was groceries that was thrown at youthrown at you

Stop a semi-truck Stop a semi-truck driving toward youdriving toward you

Put these in order:Put these in order:Least to greatest inertiaLeast to greatest inertia

Baseball bat (900g)Baseball bat (900g) Bowling ball (7.2kg)Bowling ball (7.2kg) Pencil (2.6g)Pencil (2.6g) Person (100kg)Person (100kg) Paper (0.1g)Paper (0.1g)

The greater an object’s The greater an object’s inertia, the greater theinertia, the greater the

force needed to change its force needed to change its motionmotion

Newton’s first law is often referred Newton’s first law is often referred to as the law of inertiato as the law of inertia

Units of ForceUnits of Force

SI unit of mass is kilogram (kg)SI unit of mass is kilogram (kg) SI unit of force is the NEWTON (N)SI unit of force is the NEWTON (N)

1 N of force can accelerate a 1kg object by 1 N of force can accelerate a 1kg object by 1 m/s1 m/s

4.448 N = 1 lb4.448 N = 1 lb(yes, weight is a measure of (yes, weight is a measure of

force)force)

What if there are multiple What if there are multiple forces acting on an object?forces acting on an object?

Multiple Forces Add (like in Multiple Forces Add (like in math)math)

If two or more If two or more forces are acting forces are acting on an object in the on an object in the same direction, the same direction, the netnet (overall) force (overall) force is the sum of all is the sum of all the forcesthe forces

Opposite forces subtractOpposite forces subtract

What is the net What is the net force on the ball?force on the ball?

Which way is it Which way is it going to move (if at going to move (if at all)?all)?

2.1 Section Review2.1 Section Review

1. State Newton’s first law in your 1. State Newton’s first law in your own words.own words.

2. How is mass related to inertia?2. How is mass related to inertia?

3. What is the net force and how is it 3. What is the net force and how is it determined?determined?

Important VocabularyImportant Vocabulary

ForceForce Newton’s first lawNewton’s first law NewtonNewton Net forceNet force