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Space

Gravity and Weight.

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K ey Misconceptions

Gravity

WeightT he EarthD ay and NightT he Earth, Moon and SunT he Phases of the Moon and Eclipses

T he Changing Year

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Misconceptions of Gravity Gravity is connected with air pressure and we are in anatmospheric shield which preventsthings from floating away.

T herefore there's no gravity inspace or on the moon.

Gravity is associated with rotation. If the Earth stopped spinning we¶d all

fly off.Gravity reduces with as distancebetween objects increases. T rue butmost believe it reduces a lot sooner than is actually the case.

A lternatively, gravity is only present

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Misconceptions of Weight It is possible to haveweight withoutgravity.

Weight isn't a force.

A stronauts wheremoon boots to givethen weight wherethere is no gravity

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Misconceptions of Falling Students may think thatthings µjust fall

naturally¶.O r the person lettingthem go causes theforce.

Heavier things fall toEarth faster.

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Misconceptions of

Gravity In SpaceB ound in with air pressure - no air nogravity.Gravity needs amedium, µmoleculesof gravity¶ in air.Possible Sci-Fi hasand weightlessnesshas contributed to

this.

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T eaching Gravity.

What do you think gravity is?T

ry explaining it to someone who hasnever heard of it before.

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Sir Isaac Newton.He was a scientist whowas interested in forces

and gravity.He did not discover gravity and its effectsexisted long beforeNewton.He did discover how tocalculate the force of gravity on objectsHence the forcemeasured in Newtons.

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O n the Earth, gravity pulls with a force of 10 N on every kilogram of mass. T o find the weight of a particular

mass, multiply the mass by 10. If you know the weight

and want to find the mass, divide by 10.Fill in the gaps in this table.

Object Mass (kg) Weight (N)

Television 8.0Radio 1.5

Chair 50

Bag of sugar 1.0Bottle of pop 20

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Now try these«.O b ect ass (g) ass (kg) Weight ( )

Jar o am 340 0.34 3.4ag o pasta 500

Tin o beans 450

Loa o bread 800

an o pop 330

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feel like they are upside

down?

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Gravity and Mass.Gravity is an attractive force that acts between allobjects that have mass. T he size of the force

depends on the mass of the object.A ll objects produce a gravitational force. T his is amassive force for huge masses such as planets.T hink about it - When you jump, the gravitationalforce of the Earth pulls you down . Your gravitational force is also pulling the Earthtowards you - you just don¶t notice this effectbecause your mass is so much smaller than

Earth¶s!

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Gravity and Distance.Gravitational force alsodepends on distance

between objects.Spacecraft produce avery large force, calledthrust, to overcome theforce of gravity.A s a spacecraft getsfurther away from Earth,the force of gravity getssmaller.

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H ow does the gravity on themoon differ to the gravity on

Earth?

Why?

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Spacecraft and gravity D iagrams showing thepath of spacecraft past

multiple planets/sunshow effect of gravity ontrajectory.Multi-planet maps canbe used to demonstartediffering pull betweendifferent sized objects.

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Weight , Mass and Gravity on

the Moon.T he force of gravity is lesson the Moon than on Earth.T his is because the moon

has a smaller mass than theEarth.T herefore any object willweigh less on the Moon thanon Earth.A

n A

stronaut could jump 20feet in to the air on the Moonbecause gravity is less.However, the astronaut stillhas the same body andmass. He just weighs lessbecause gravity is weaker on

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T alking about weight and

mass.A scientist should never say:

³She/he weighs 50 kilograms,´but should always say:

³She/he has a mass of 50 kilograms,´

A lternatively, the scientist could say:³T he gravitational force acting on her/his

mass is about 500 Newtons.´T his is the same as saying:

³His/her weight is about 500 Newtons.´

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Experiments.D ropping two similar sized objects to seewhich lands first.µFeather and a steelball¶A lternatively usethe I O P tennis ballexample.

http://www.youtube.com

/watch?v=PE81zGhnb

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Experiments.Some free to downloadgames looking at how

spacecraft paths usegravitational slingshots

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Experiments.U se a cup full of water (over a bucket!) to

demonstrate that cupand water fall at samerate.D rill holes in the cup toshow that water stopsflowing out when in

freefall .

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And of course, songs!