Forces and Motion

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Forces and Motion
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Forces

• A force is a push or a pull.
• Force generates energy.
• Objects stay in place unless a force starts them
  moving.
• How a force affects an object depends on its
  mass.
• A newton is a metric unit of force.

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What is Gravity?

• Gravity is the word we use to describe the
  pull between masses.

Things with more MASS produce a greater Gravity
pull on each other.
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Gravity controls.

• A roller coasters ride
• A divers dive
• A skiers jump
• A baseballs fall

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What word describes how much of you there is?
Mass
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Mass
Id eat a looott of yummy bread to gain mass!
Your mass is the amount of material that your
body contains. How can you gain mass?
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Does something that is bigger always have more
mass?
No! Not Always!
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Does bigger more mass?
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So, having more mass does not mean taking up more
space!
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Mass vs. Weight
Do things that have more mass always weigh more?
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Not Always!

• When you stand on a bathroom scale, the scale is
  made of springs. The farther down you push the
  springs, the higher the number on the scale. The
  number tells you your weight. On earth it is
  true that the more mass you have, the more weight
  you have.

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Weight? Mass? I am totally confused!
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Pretend That You Are in Space!
Oh where, oh where, has my weight gone? Oh
where, oh where can it be?
You are floating around. You drift over to a
floating bathroom scale and put your feet on it.
Your feet do not push down on the scale at all.
The scale shows that you weigh 0. You have lost
your weightbut did you lose your mass?
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All my body parts are still togetherso I still
have mass!
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On a space flight, your mass would be the same
but your weight would change.
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Summing up Mass and Weight

• Your MASS is the amount of material in your body.
• Your MASS doesnt depend on where you are.
• Your WEIGHT is how much your body pushes down on
  a scale.
• Your WEIGHT depends on how much MASS you have and
  where you are.

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Where would you weigh the most?
OR
Earth
Moon
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• Remember, gravity describes the pull between
  masses. You have mass, and the earth has mass.
  There is a pull between you and the earth. We
  measure this pull with a scale. The more the
  gravity, the greater the squeeze on the springs
  of the scaleand the more you weigh.

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Gravity and Weight Summary

• Your weight on earth is a measure of the GRAVITY
  pull between you and the earth. Bodies with more
  MASS produce a greater GRAVITY pull on each other.

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On Earth
So, if I ate a lot of yummy tuna fish while
standing on the scale, I would gain mass.
The pull between the earth and me would become
greaterand I would weigh more!
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Back to the Moon
During my trip to the moon, my mass does not
change, but the moon has much less mass than the
earth.
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Still on the Moon!
There is less gravity pull between you and the
moon. If you stood on the scale on the moonyou
would weigh less than on earth!
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Summary

• Forces in nature include gravity and friction.
• Gravity keeps you on earth.
• Weight is the measure of the force of gravity.