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What are we le arning about t oday?

What are we learning about today? What are we learning about today?

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Page 1: What are we learning about today? What are we learning about today?

What are we learning about today?

Page 2: What are we learning about today? What are we learning about today?

GravityGravityWhat is it?What is it?

https://www.youtube.com/watch?v=mezkHBPLZ4A

Page 3: What are we learning about today? What are we learning about today?

GravityGravity isis…… A natural force that A natural force that

pulls all objects pulls all objects toward the center toward the center

of the earth.of the earth.

http://www.neok12.com/video/Gravitation/zX64676359061f6b43074555.htm

Page 4: What are we learning about today? What are we learning about today?

WHAT IS A FORCE?WHAT IS A FORCE?

A pull or a push on an

object

It is measured in Newtons (N)

or kg/ m/ s2.

Page 5: What are we learning about today? What are we learning about today?

Newton was a Smart GuyNewton was a Smart Guy

Sir Isaac Newton (1643-1727) an Sir Isaac Newton (1643-1727) an English scientist and mathematician English scientist and mathematician famous for his discovery of the law of famous for his discovery of the law of gravity also discovered the three gravity also discovered the three laws of motionlaws of motion

Today these laws are known as Today these laws are known as Newton’s Laws of MotionNewton’s Laws of Motion and and

describe the motion of all objects on describe the motion of all objects on the scale we experience in our the scale we experience in our

everyday lives.everyday lives.

Page 6: What are we learning about today? What are we learning about today?

11stst law: law: An object at rest tends to stay at An object at rest tends to stay at rest and an object in motion tends to stay rest and an object in motion tends to stay

in motion unless acted upon by an in motion unless acted upon by an unbalanced forceunbalanced force..

Things will keep Things will keep moving forevermoving forever unless it is unless it is stopped by a force.stopped by a force.

Things will stay Things will stay stationarystationary (in one place) (in one place) unless an unless an outside forceoutside force acts on it. acts on it.

If a golf ball was hit in space would it stop?If a golf ball was hit in space would it stop? If a golf ball was hit on Earth, would it to stop? If a golf ball was hit on Earth, would it to stop?

What causes is to stop? What causes is to stop?

Earth’s Gravity causes things to stop. The opposing Earth’s Gravity causes things to stop. The opposing force that occurs by making contact with another object is force that occurs by making contact with another object is called called FrictionFriction

http://www.sciencechannel.com/games-and-interactives/newtons-laws-of-motion-interactive/

Page 7: What are we learning about today? What are we learning about today?

FrictionFriction:: a force that opposes the motion a force that opposes the motion of objects that touch as they move past of objects that touch as they move past each other. each other.

Without friction, the world would be a very Without friction, the world would be a very different place. In a frictionless world, different place. In a frictionless world, every surface would be more slippery than every surface would be more slippery than a sheet of ice. a sheet of ice.

Your food would slide off your fork. Your food would slide off your fork. Walking would be impossible. Walking would be impossible.

Cars would slide around Cars would slide around helplessly with their helplessly with their wheels spinning. wheels spinning.

Magic School Bus Clip

Page 8: What are we learning about today? What are we learning about today?

Some Examples from Real LifeSome Examples from Real Life

Two teams are playing tug of war. They are both Two teams are playing tug of war. They are both exerting exerting equal forceequal force on the rope in opposite on the rope in opposite directions. This directions. This balanced forcebalanced force results in no results in no change of motion.change of motion.

A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

Page 9: What are we learning about today? What are we learning about today?

Newton’s First Law is also Newton’s First Law is also called the called the Law of InertiaLaw of Inertia

InertiaInertia: the tendency of an object to resist : the tendency of an object to resist changes in its state of motionchanges in its state of motion

The First Law states that The First Law states that all objects have all objects have inertiainertia..

***The more ***The more massmass an object has, the more an object has, the more inertia it has (and the inertia it has (and the harderharder it is to it is to change its motion).change its motion).

http://www.nbclearn.com/nhl/cuecard/56615http://www.nbclearn.com/nhl/cuecard/56615

Page 10: What are we learning about today? What are we learning about today?

More Examples from Real LifeMore Examples from Real LifeA powerful locomotive begins to pull a long line of boxcars that were sitting at rest. Since the boxcars are so massive, they have a great deal of inertia and it takes a large force to change their motion. Once they are moving, it takes a large force to stop them.

On your way to school, a bug flies into your windshield. Since the bug is so small, it has very little inertia and exerts a very small force on your car (so small that you don’t even feel it).

Page 11: What are we learning about today? What are we learning about today?

22ndnd law: law: Force equals mass Force equals mass times acceleration.times acceleration.

This equation helps teach us that This equation helps teach us that GravityGravity is a is a forceforce..

AccelerationAcceleration is how quickly an is how quickly an object is object is changing speedchanging speed

Earth’s gravity has a constant Earth’s gravity has a constant acceleration acceleration downwarddownward. All objects . All objects accelerate at accelerate at 9.89.8 m/s m/s22. .

If we all jumped out of a plane we If we all jumped out of a plane we would fall at 9.8 m/swould fall at 9.8 m/s22. This goes for . This goes for all other objectsall other objects whether whether largelarge or or smallsmall..

Page 12: What are we learning about today? What are we learning about today?

Which do you think would fall first?Which do you think would fall first?

A A bouncybouncy ballball

Or a marble

Try It!http://indianapublicmedia.org/amomentofscience/ground-golf-bowling-ball/

Page 13: What are we learning about today? What are we learning about today?

They fall at the They fall at the same ratesame rate of of speedspeed, , because of Earth’s constant because of Earth’s constant

downward acceleration. downward acceleration. ButBut the the marble has more marble has more mass mass (weight) (weight)

and so gravity makes it and so gravity makes it fall harderfall harder and and hitshits the earth with the earth with more forcemore force!!

GravityGravity has a has a stronger forcestronger force on on things with things with more massmore mass!!

Page 14: What are we learning about today? What are we learning about today?

It takes force to overcome gravity!It takes force to overcome gravity!

Throw a bean bag in the air and then…

Throw a basketball in the air.

Which one was harder to throw?

The basketball would be harder The basketball would be harder to throw. You had to use to throw. You had to use more more forceforce to throw the basketball to throw the basketball because it has because it has more massmore mass (weight)(weight)

Page 15: What are we learning about today? What are we learning about today?

What does F = ma say?What does F = ma say?F = ma basically means that the force of an

object comes from its mass and its acceleration.

Something very small (low mass) that’s changing speed very quickly (high acceleration), like a bullet, can still have a great force. Something very small changing speed very slowly will have a very weak force.

Something very massive (high mass) that’s changing speed very slowly (low acceleration), like a glacier, can still have great force.

Page 16: What are we learning about today? What are we learning about today?

Using Force = mass x acceleration Using Force = mass x acceleration

Calculate which would land with Calculate which would land with more force:more force: Object 1 has a mass of 20 gramsObject 1 has a mass of 20 grams Object 2 has a mass of 100 gramsObject 2 has a mass of 100 grams Acceleration is 9.8 m/sAcceleration is 9.8 m/s22..

Force of Object 1?Force of Object 1? Force of Object 2?Force of Object 2?

http://www.pbs.org/opb/circus/classroom/circus-physics/activity-guide-newtons-laws-motion/

Page 17: What are we learning about today? What are we learning about today?

33rdrd Law: Law: For every action there is For every action there is an equal and opposite reaction.an equal and opposite reaction.~ For every force acting on an object,

there is an equal force acting in the opposite direction.

Right now, gravity is pulling you down in your seat, but Newton’s Third Law says your seat is pushing up against you with equal

force. This is why you are not moving. There is a balanced force acting on you– gravity pulling down, your seat pushing up.

http://www.pbs.org/opb/circus/classroom/http://www.pbs.org/opb/circus/classroom/circus-physics/activity-guide-newtons-laws-circus-physics/activity-guide-newtons-laws-motion/motion/

Page 18: What are we learning about today? What are we learning about today?

Think about it . . .Think about it . . .What happens if you are standing on a skateboard or a slippery floor and push against a wall? You slide in the opposite direction (away from the wall), because you pushed on the wall but the wall pushed back on you with equal and opposite force.

Why does it hurt so much when you stub your toe? When your toe exerts a force on a

rock, the rock exerts an equal force back on your toe. The harder you hit your toe

against it, the more force the rock exerts back on your toe (and the more your toe

hurts).

http://www.quia.com/quiz/1321898.html

Page 19: What are we learning about today? What are we learning about today?

Satellites move Satellites move fast enoughfast enough that they that they overcomeovercome earth’s earth’s gravitational pullgravitational pull, but , but

still stay within the earth’s orbit.still stay within the earth’s orbit. As you know Satellites move around our earth. As you know Satellites move around our earth.

But did you know that is a problem?But did you know that is a problem?

Page 20: What are we learning about today? What are we learning about today?

““There are currently over eight There are currently over eight thousand satellites and other thousand satellites and other large objects in orbit around the large objects in orbit around the Earth, and there are countless Earth, and there are countless smaller pieces of debris smaller pieces of debris generated by spacecraft generated by spacecraft explosions and by collisions explosions and by collisions between satellites. Until between satellites. Until recently, it has been standard recently, it has been standard practice to put a satellite into practice to put a satellite into orbit and leave it there. orbit and leave it there. However, the number of However, the number of satellites has grown quickly, and satellites has grown quickly, and as a result, the amount of orbital as a result, the amount of orbital debris is growing rapidly. debris is growing rapidly. Because this debris is travelling Because this debris is travelling at orbital speeds (7-8 km/s!), it at orbital speeds (7-8 km/s!), it poses a significant threat to the poses a significant threat to the space shuttle, the International space shuttle, the International Space Station, and the many Space Station, and the many satellites in Earth orbit.”satellites in Earth orbit.”

http://images.google.com/imgres?imgurl=http://http://images.google.com/imgres?imgurl=http://www.tethers.com/WebImages/www.tethers.com/WebImages/OrbitalDebris.jpg&imgrefurl=http://www.tethers.com/OrbitalDebris.jpg&imgrefurl=http://www.tethers.com/OrbitalDebris.html&usg=__JnSEf589SrzzPevOvU5XTyPALss=&h=2OrbitalDebris.html&usg=__JnSEf589SrzzPevOvU5XTyPALss=&h=250&w=258&sz=46&hl=en&start=18&tbnid=rrwVQ4lVZalWAM:&t50&w=258&sz=46&hl=en&start=18&tbnid=rrwVQ4lVZalWAM:&tbnh=109&tbnw=112&prev=/images%3Fq%3Dearth%2B%252Bbnh=109&tbnw=112&prev=/images%3Fq%3Dearth%2B%252B%2Bsatellites%26gbv%3D2%26hl%3Den%26safe%3Dactive%2Bsatellites%26gbv%3D2%26hl%3Den%26safe%3Dactive

Page 21: What are we learning about today? What are we learning about today?

When do Satellites become subject to earth’s When do Satellites become subject to earth’s gravity?gravity?The cannon ball must The cannon ball must

move move very quicklyvery quickly to to orbit orbit the earth.the earth.

If an object does not If an object does not meet the required meet the required speed it would be speed it would be slowly draggedslowly dragged into into the Earth’s the Earth’s atmosphere. atmosphere.

* Objects* Objects fartherfarther from from earthearth experience experience less less gravitational pullgravitational pull..The closer to earth’s surface the more

gravitational pull is felt.

Page 22: What are we learning about today? What are we learning about today?

The Moon orbits the Earth and is The Moon orbits the Earth and is therefore a Satellite.therefore a Satellite.

Despite that the moon is much Despite that the moon is much fartherfarther it is it is still attractedstill attracted to the to the Earth’s gravitational pull, but it Earth’s gravitational pull, but it moves so quickly it moves so quickly it revolvesrevolves the the planet at a fixed distance.planet at a fixed distance.

Page 23: What are we learning about today? What are we learning about today?

The Moon is The Moon is also also 1/161/16 the the size of the size of the earth and earth and therefore has therefore has 1/161/16 of the of the gravitational gravitational pull.pull.

Earth’s gravity Earth’s gravity is is 9.8 9.8 m/sm/s22..

Moon’s gravity Moon’s gravity is is .1625.1625 m/s2. m/s2.

Page 24: What are we learning about today? What are we learning about today?

State Objectives…State Objectives…Distinguish between mass and weight…Distinguish between mass and weight…

MassMass: the amount of matter in an : the amount of matter in an objectobject

WeightWeight: the force of gravity acting on : the force of gravity acting on an object an object

How is weight determined?How is weight determined? ScalesScales

Page 25: What are we learning about today? What are we learning about today?

If you went to Mars would you If you went to Mars would you massmass be the same or different?be the same or different?

SAMESAME

If you went to Mars wouldIf you went to Mars would you you weightweight be the same be the same or different?or different?

DifferentDifferent

Page 26: What are we learning about today? What are we learning about today?

Cite examples of how Earth’s Cite examples of how Earth’s gravitational force on an object gravitational force on an object depends upon the mass of the object. depends upon the mass of the object.

MoonMoon Satellites Satellites Both have less mass than Earth and Both have less mass than Earth and

therefore are pulled in by Earth’s therefore are pulled in by Earth’s gravitygravity

Page 27: What are we learning about today? What are we learning about today?

Describe how Earth’s gravitational Describe how Earth’s gravitational force on an object depends upon the force on an object depends upon the distance of the object from Earth. distance of the object from Earth.

Moon vs. MarsMoon vs. Mars