Newton’s Laws

1

Newton’s LawsThe Father of Force

Isaac Newton(1642 – 1727)

2

What is a Force?

Force can be defined as a push or a pull.

Or anything else that has the ability to change motionOr anything else that has the ability to change motion

3

Force:

kg x m/s2

kilogram x m/sec2

NN Is even easier!Is even easier!

Easier than saying kilogram Easier than saying kilogram m/sec m/sec22

4

To Understand Force…

You must understand the difference between

AND

2 Kg Mass

5

What is MassMass?

1 KgMass

2 KgMass

1.5 KgMass

The amount of “stuff” in an object.

MassMass is measured in KilogramsKilograms

6 How is Mass Different Than Weight?

1.0 Kg1.0 KgMassMass

2.2 pounds2.2 pounds

9.8 N9.8 N



14.8 N14.8 N



19.7 N19.7 N

Weight is measurement of FORCE.Weight is measurement of FORCE.

DON’T USE kilogramskilograms (kg) (kg) as a measurement for weightweight (force) (force) USEUSE pounds (lb) or N for force pounds (lb) or N for force.

(1 kg x 9.86 m/s(1 kg x 9.86 m/s22)) (1.5 kg x 9.8 6m/s(1.5 kg x 9.8 6m/s22)) (2 kg x 9.86 m/s(2 kg x 9.86 m/s22))

force due to force due to gravity gravity

(9.8 m/s(9.8 m/s22))

force due to force due to gravity gravity

(9.8 m/s(9.8 m/s22))

force due to force due to gravitygravity

(9.8 m/s(9.8 m/s22))

7

http://www.exploratorium.edu/ronh/weight/

1 KgMass

2.2 Pounds

On the sunOn the sun 1.0 kg1.0 kg wouldwould weigh 59.5 lbs weigh 59.5 lbs

On MarsOn Mars 1.0 kg1.0 kg wouldwould weigh 0.8 lbs weigh 0.8 lbs

On the moonOn the moon 1.0 kg1.0 kg would would weigh 0.3 lbs weigh 0.3 lbs

Different Gravity? Different Gravity? Mass is the Same:1 kgMass is the Same:1 kgBut the WEIGHT…But the WEIGHT…

What’s “Your Weight On Other Worlds?”

7

http://www.exploratorium.edu/ronh/weight/

8

Let’s look at Newton's three laws of motion...

These laws explain why objects move (or don't move).

9

An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will

continue with constant speed and direction, unless acted on by an unbalanced force.

This law shows how force, mass and acceleration are related as shown in the equation below:

Force = mass x acceleration

For every action there is an equal and opposite reaction

10 Newton’s First Law: Balanced Forces

Forces that are balanced can be:

In MotionNot in motion

Stay at rest: a book on a table

Stay in motion: a bowling ball tossed

in space

InertiaInertia

An object will maintain a constant state of motion (balanced). This means an object at rest tends to stay at rest

and an object in motion tends to stay in motion

It will go on and on forever

This is known as

IP&C

Table pushes up on book

Gravity pulls down on book

11 Newton’s First Law: Unbalanced Forces

The book below slides and then stops because resistant force called friction. Friction is force that opposes motion.

In space there is no resistance to cause friction, so a bowling ball would stay in motion ...unless another object got in the way…

It kind of reminds of

a few movies I’ve seen

lately...

An unbalanced force is a force that changes the motion.

IP&C

Force of friction stops the book

12

Of course “frictional” force happens on earth...

But, if you weren’t wearing a safety belt

You would continue your motion…

Don’t let this happen to you, buckle up!

13

Force and acceleration are related

Newton’s Second Law: Force = Mass X Acceleration

You are going down the road on your inline skates. Suddenly you look to your right and see a car accelerating faster coming right for YOU! You look for an escape to your left… Oh no! There’s a rock at the edge of neatly manicured lawn. Which will you choose...

A massive car accelerating faster? ...or a medium size rock not in motion?

GoodChoice

Force (car) = mass x acceleration is greater than

Force (rock) = mass x acceleration

You still might get hurt, but would be much worse off choosing the force of the car over the force of the rock.

14

Solving Force Problems

Step 1 Read the problem and write downthe formula you will use.

Step 2 Plug in the information you know into the formula.

Step 4 Write down the answer with thecorrect units.

Step 3 Solve the math.

15

“How much force is needed to accelerate a 1400-kg car 2 m/s2? ”

Consider the problem…

F =m =a =

Formula Plug-in Answer

Units, units, units!

Step 1 Read the problem, draw a picture

1400-kgcar

2 m/s2

How much force?

16

F =m =a =



1400 kg2 m/s2

Step 2 Write down what you know, What are you trying to find?

1400-kgcar

2 m/s2


17



Step 3 Set up the formula,

F =m =a =

1400 kg2 m/s2

m x a


F = m x a

18



Step 4 Plug in the numbersSolve

2800kg x m/s2

F =m =a =

1400 kg2 m/s2


m x a 1400 kg x 2 m/s2 2800 kg x m/s2

19

Be sure to do the problems:

• Helpful Hints:a = F / m

F = m x a

m = F / a

20The unit for force:

1 kg x m/s2 = 1 newton or 1N

…I thought so.

Which one would you rather write for your answer?

2800 N

21 Newton’s Third Law: Action / Reaction


Look at the picture below:

What is the action?

What is the reaction?

As the gases push downward out of the rocket,

The the rocket is pushed upward by the gases

22

An object will remain at rest unless acted upon by an “unbalanced” force. An object in motion will

continue with constant speed and direction, unless acted on by an unbalanced force.

This law shows how force, mass and acceleration are related as shown in the equation below:

Force = mass x acceleration


23 Newton’s Laws explain how Earthquakes create such devastation

Most of the time the Earth’s massive plates Most of the time the Earth’s massive plates push on each to move very slowly.push on each to move very slowly.

But, sometimes a massmassive plate exerts a greater amount of forceforce that accelerate another plate.

To learn more go to: http://vcourseware5.calstatela.edu/VirtualEarthquake/VQuakeIntro.html

This results in an earthquake.This results in an earthquake.

http://vcourseware5.calstatela.edu/VirtualEarthquake/VQuakeIntro.html

24 The Story of Newton’s AppleNewton sat under an apple tree and an apple fell on his head.

That falling apple gave him a revelation.

GRAVITY.GRAVITY.But DON’T think of gravity as falling…

It is the pull (force) that an object has on another.

And led him to describe a force called...

25

Newton’s apple was falling because the massive gravitational force of the Earth was pulling the apple towards

Earth...

26 Gravity is the force that ALL objects in the UNIVERSE exert on each other...

Newton said that gravitational force depends on 2 things2 things:

The DISTANCEDISTANCE of the objects The MASSMASS of the objects

LESS gravitational force compared to...

MORE gravitation force here.

The blue objectblue object has more gravitational force than the green objectgreen object because the blue objectblue object has more MASSMASS.

27Newton’s apple fell because the Earth’s pull

of gravity....

was more massive was more massive than the than the apple’sapple’s pull pull of gravity on of gravity on

the Earththe Earth

The itty-bitty pull of apple is too small to pull the Earth, so it is pulled to the Earth...

28

The moon is a satellite too..

The pull of gravity keeps satellites orbiting around

the Earth

29

The Earth is round The Earth is round and the satellite and the satellite

continues to “just continues to “just miss” entering into miss” entering into

the Earth’s the Earth’s atmosphere.atmosphere.

Satellites are sent away and placed in the exact spot where the Earth’s gravity pulls them into a “continuous free fall” or orbit... The moon does

the same thing.

30 Does the moon’s gravitational pull effect the Does the moon’s gravitational pull effect the Earth? Earth? Yes, the moon’s

gravity is large enough to actually pull water out of the ocean from space…

Well, not quite that much...just enough to create motion of the

tides.

31

Newton is even credited with inventing

CALCULUS.Needless to say, Newton was Needless to say, Newton was very important in shaping our very important in shaping our

understanding of scienceunderstanding of science

Documents

Newton’s Laws