1 the physics of toys (and space) addendum to curriculum for ms. decker’s 2 nd grade class...

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The Physics of Toys (and Space)Addendum to curriculum

for Ms. Decker’s 2nd Grade ClassJamestown ElementaryBy Darren McKnight

Spring 2001

1. Force and Friction

2. Energy and Machines

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Force – Key Points

• What is a force?

• Why does gravity exert a force on you?

• If an object is not moving does that mean that there are no forces on it?

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Force – Key Points Answers

• What is a force?– Something that pushes or pulls you

• Why does gravity exert a force on you?– Two objects with mass attract each other

• If an object is not moving does that mean that there are no forces on it?– It may but it probably means that the forces

acting an object cancel out

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ForcesThe man is standing still.Are there any forceson the man?

If so, draw them.

floor

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ForcesThe force due to gravityis pushing him down.

Is there another force?

Gravity

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ForcesThe other force is the floor pushing back!

Which force is greater?

Gravity

Floor

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ForcesThe force due to gravityis the same in size,but opposite indirection, to the forceby the floor!!!!

Floor

Gravity

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Gravitational Force - Questions

• So what causes a gravitational force?

• Is there a gravitational force on the moon?– Is it larger or smaller than the gravitational

force on the Earth?

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Gravitational Force - Answer

• So what causes a gravitational force?– Two objects are attracted to each other

Object 2 (has mass)

Object 1 (has mass)

F1

F2

F1 = F2

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Gravitational Force

• Gravitational force keeps us “stuck” to the Earth!!!• We actually pull on the Earth but the Earth is too big to move!!!

Earth

Person

F

F

Fperson = Fearth

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Gravitational Force - Questions

• Is there a gravitational force on a person standing on the moon?– Is it larger or smaller than the gravitational

force on the Earth?

– Why?

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Gravitational Force -Answers

• Is there a gravitational force on the moon?– Is it larger or smaller than the gravitational

force on the Earth?• The gravitational force is smaller on the moon.

– Why?• The moon is smaller (less massive) than the Earth.

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Force – Key Points

• What is a force?

• Why does gravity exert a force on you?

• If an object is not moving does that mean that there are no forces on it?

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Final Force ExampleMs. Decker at the Pool

. - What forces are acting on Ms. Decker as she standson the end of the diving board?- Draw them.

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Final Force ExampleMs. Decker at the Pool

.

- What forces are acting on Ms. Decker as she standson the end of the diving board?

Force from divingboard

Force from Ms. Decker (gravity)

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Final Force Example Ms. Decker at the Pool

- Which force is greater?.

Force from divingboard

Force from Ms. Decker (gravity)

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Final Force Example Ms. Decker at the Pool

-Which force is greater?They are equal sinceMs. Decker is not moving

.

Force from divingboard

Force from Ms. Decker (gravity)

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Final Force Example Ms. Decker at the Pool

. -What if Ms. Decker walks off the end of the diving board?

- Why?

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Final Force Example Ms. Decker at the Pool

.

-What if Ms. Decker walks off the end of the diving board?She starts to fall toward the water- Why?Gravity is still forcing down but thereis no force from the diving board- Draw the forces on Ms. Decker.

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Final Force Example Ms. Decker at the Pool

.

-Draw the forces on Ms. Decker.

-Why does Ms. Decker continue to fall?Gravity

Air Resistance

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Final Force Example Ms. Decker at the Pool

.

-Why does Ms. Decker continue to fall?The force due to gravity is greater thanair resistance force opposing her fall.

- What happens when Ms. Decker hitsthe water.

Gravity

Air Resistance

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Final Force Example Ms. Decker at the Pool

.

-What happens when she hits the water?

She gets wet!!!

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Friction – Key Points

• What is friction?

• What makes friction greater?

• What makes friction less?

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Friction

• Rubbing – create heat or slow down motion or both– What are examples of friction?

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Friction

• Rubbing” – create heat or slow down motion or both– What are examples of friction?

• Rubbing hands together to get warm

• Putting sand on the road to prevent cars from sliding

• Newspaper sliding across the driveway

• Any more?

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Friction

• Two items determine the friction force– YES, FRICTION CREATES A FORCE!!!

• 1. Goes against the motion • 2. Greater if surfaces are rough ; less is surfaces are smooth

• If we slid a book across the two surfaces below, on which one would the book go farther?

A B

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Friction

• If we slid a book across the two surfaces below, on which one would the book go farther?

A

• Draw the forces on book.

A B

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Friction

• Draw the forces on book.

ATable

Book (gravity)

Friction

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Friction in Space

• Is there any friction in space?

• Is there any friction when objects come back from space?

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Friction in Space• Is there any friction in space?

– No, no air or surfaces to slide against

• Is there any friction when objects come back from space?– Yes, the air creates a surface and a tremendous amount

of heat when objects comes back to Earth.– Manned spacecraft have special heat shields so that

they do not burn up!!!!!!!– Shooting stars are just cosmic “pebbles” burning up as

they come into the Earth’s atmosphere

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Reentering Space Vehicle

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Friction – Key Points

• What is friction?– A force that opposes motion

• What makes friction greater?– Rougher surface

• What makes friction less?– Smoother surface

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Friction – Final Example

Draw the forces on the picture. Hint: The puck is slowing downas it moves across the table.How could you increase the distance the puck would slide?

The puck is sliding this way…

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Friction – Final ExampleDraw the forces on the picture. Hint: The puck is slowing downas it moves across the table.How could you increase the distance the puck would slide?Polish the table or polish the bottom of the puck – reduce friction!!!!

The puck is sliding this way…

Force from table

Force due to gravity

Friction

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Friction Lab

• We will slide three pucks at the same speed and measure how far they go

• We will plot the data and make observations

• Why might different pucks go different pucks go different distances?

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Friction Lab

• Why might different pucks go different distances?– The bottom surfaces might be smoother or rougher than

the others

• Everyone will record all of the data – I will call off distance traveled and puck letter (A, B, or

C)

• Who wants to volunteer to slide the puck?

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Friction Lab Data

A B C Puck

18ft

15ft

12ft

9ft

6ft

3ft

For example, the plot above shows puck A going 10ft and 15ftwhile puck B went 6 ft and 9ft

X

XX

X

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Friction Lab Data

A B C Puck

18ft

15ft

12ft

9ft

6ft

3ft

Which puck traveled the farthest?________What does that mean?___________________________Which puck had the most friction?_________

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Big Word of the Day

• A surface that is very rough means it has a high coefficient of friction!

• Very impressive word to use at home!– “Gee Mom, our tires have a very high

coefficient of friction!”– “Hey Dad, that icy road has a very low

coefficient of friction!”

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The Physics of Toys (and Space)Addendum to curriculum

for Ms. Decker’s 2nd Grade ClassJamestown ElementaryBy Darren McKnight

Spring 2001

1. Force and Friction

2. Energy and Machines

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Potential and Kinetic Energy – Key Facts

• Potential energy – “stored” energy– How can we “store” energy?

• Kinetic energy – energy of movement– How is potential energy converted into kinetic energy?

• What is work?– Exert a force over a distance

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Potential Energy

Does the ballhave any storedenergy here?

Does the ballhave any storedenergy here?

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Potential Energy

Does the ballhave any storedenergy here?

Does the ballhave any storedenergy here?

NOYES, we moved the ballagainst gravity (did work)

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Force Review

What forces are acting on the ball while wehold it still above the floor?

Draw and label them.

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Force Review

Which force is greater?They are the same, that is whythe ball is not moving!!!

Force of the hand

Force due to gravity

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Potential Energy

What happens when we let goof the ball?

If the ball is to move show the direction of the ball.

Label the forces on the ball!!!!

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Potential/Kinetic EnergyWhat happens when we let goof the ball?

It starts to fall – has kinetic energyIf the ball is to move show the direction of the ball.

Label the forces on the ball!!!!Gravity is larger force than air resistance

velocity

Gravity

Air resistance

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Potential and Kinetic Energy – Key Facts

• Potential energy – “stored” energy– How can we “store” energy?

• Kinetic energy – energy of movement– How is potential energy converted into kinetic energy?

• What is work?– Exert a force over a distance

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Swing Set and Energy

Does a swing have any kineticenergy when it is sitting stillunused? How about potentialenergy?KE _____ PE _____

Does a swing have any kineticenergy when it is pulled up?How about potential energy?

KE _____ PE _______

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Swing Set and Energy

Does a swing have any kineticenergy when it is sitting stillunused? How about potentialenergy?KE __no_ PE _some_

Does a swing have any kineticenergy when it is pulled up?How about potential energy?

KE __no_ PE __more___

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Swing Set and Energy

What happens when you letgo of the swing to the kinetic energy and potential energy?KE _____ PE _____

As the swing gets to the bottom again what is the energy?KE _____ PE _______

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Swing Set and Energy

What happens when you letgo of the swing to the kinetic energy and potential energy?KE _starts_ PE _goes down_

As the swing gets to the bottom again what is the energy?KE _maximum_ PE _minimum_

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Swing Set – Exchanging Energy

• So as the swing oscillates (another big word to use at home – means “go back and forth”) it exchanges kinetic energy for potential and back again

• Why does the swing always eventually stop?

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Swing Set – Exchanging Energy

• Why does the swing always eventually stop?– Friction from where the chain attaches to the

swing set– Air resistance

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Springs

• What are springs used for?

• Can you describe how a spring “stores” energy?

• Can you describe how a spring releases kinetic energy?

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Spring as a “Worker”Spring PE KE

Relaxed None None

Squeezed Maximum None

Released Some Some

Back to Middle None MaximumV

V

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Spring Lab

• You will observe – 1. How potential energy is stored in a spring

(compress the spring) and– 2. Then converted into kinetic energy (the

spring flies up with some velocity) and– 3. Then converted back into potential energy

(jumping up a certain distance)

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Spring Lab• Step 1: Compress spring a certain amount

– A little (first mark)– A lot (second mark)– All the way (third mark)

• Step 2: Let the spring go!• Step 3: Record how high up the

spring goes on the stick– Stick is marked in one foot sections by color

Work in pairs and put answers on the empty table

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Data Collection for Spring LabPress Down the Spring How High it Jumps

A little brown

A little

A little

A lot pink

A lot

A lot

All the way red

All the way

All the way

The table above shows three example experiments: when the spring waspushed down a little it stayed in brown, for “a lot” it went to pink, and when compressed “all the way” it went all the way to the red.

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Data Collection for Spring LabPress Down the Spring How High it Jumps

A little

A little

A little

A lot

A lot

A lot

All the way

All the way

All the way

Explain what is happening in your own words:_____________________________________________________________________________________________________________________________

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Observations from Spring Lab

• The more you compress the spring the farther up it jumps– Give it more potential energy (stored in the

spring) then it has a greater kinetic energy (shoots up higher)

• What causes the spring to slow down and eventually stop?

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Observations from Spring Lab

• What causes the spring to slow down and eventually stop?– Gravity is acting down on the spring slowing it

down– There is probably some friction between the

spring and the stick

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Satellites in Orbit

• Satellite is an object that goes around and around another object– The moon is a satellite of the Earth– The space shuttle is a satellite when it goes into

space– The Earth is a satellite around the Sun

• A satellite in orbit is much like a swing!!!

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Satellites in Orbit

A B

At point A the satellite is closest to the Earth and at Point B itis farthest from the Earth.What does that mean about its potential energy at points A and B?

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Satellites in Orbit

A B

What does that mean about its potential energy at points A and B?Lowest potential energy at A and highest at B

So what do you think is true about the kinetic energy at points A and B?

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Satellites in Orbit

A B

So what do you think is true about the kinetic energy at points A and B?

The kinetic energy is smallest at point B (slowest) and largest point A (fastest)

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Machines – Key Facts

• What is a machine?

• Name some examples?

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Machines – Key Facts

• What is a machine?– Something that uses energy to do useful activities

• Name some examples?– Levers

– Wheels and axles

– Pulleys

– Inclined planes

– Screws

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Space Machines• Momentum wheel – spin up a wheel

to keep an object oriented

• Rocket – burn fuel, send exhaustout back so rocket moves forward

• Solar Panels – convert sunlightinto electricity

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Space Machines - Rockets

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Space Machines - Satellites

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Space Machines - Satellites

Hubble Space Telescope

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Releasing The Hubble1

2

3

4What kind of machinepicked up the Hubbleand put it into space?

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Space Machines - Satellites

Hubble Space Telescope – broken into pieces

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Space Machines on Moon or Other Planets

Moon Mars

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Space Physics – Overall Example

• Forces

• Energy – Potential and Kinetic

• Machines

• Friction

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Rocket on the Launch Pad

What forces are acting on the rocket?

Draw on the forces.

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Rocket on the Launch Pad

What forces are acting on the rocket?

Force due to gravity

Force from the ground

gravity

Ground

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Rocket on the Launch Pad

What will happen when the rocket starts?

Draw on the forces.

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Rocket on the Launch Pad

What will happen when the rocket starts?

Force from the rocket is biggerthan the force due to gravityand the air resistance

rocket

gravity

Airresistance

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Releasing the Satellite

• When the rocket gets into space how might the satellite be pushed away from the rocket?

– Hint: What lab did we do where we store potential energy in a simple device that was later turned into kinetic energy?

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RIGHT!!!! Springs are Used

Last rocket

springs

The cover also needs tobe taken off… How?Why do you think we neededa cover?

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Satellite Then Unfolds Using a Small Motor

Now it continues to goaround and around theEarth.What do we call that?

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Satellite in Orbit

Where the satellite is located right now, what can you say aboutthe kinetic and potential energy of the satellite?___________________________________________________

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Satellite Reenters

• Eventually the satellite comes back to Earth – WHY?

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Satellite Reenters

• Eventually the satellite comes back to Earth – WHY?

• Air resistance from the atmosphere will slow it down

• Maybe a rocket was fired to bring it back to Earth

• What happens to the satellite as it reenters?

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Satellite Reenters

• What happens to the satellite as it reenters?– It heats up and slows down due to friction

• It might melt and burn up completely depending on what it is made of….

• Now you know all about rocket, satellites, and space physics!!!!!

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Physics and Science are Very Important – Explain what is

happening around you everyday!

89Miss Decker’s Class May 2001

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