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.
• A newton is a metric unit of force.

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Applying Force

• How do you know what direction an object will
  move?
• How do you know how fast an object will move?

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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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Force and Mass

• How a force affects an object depends on its
  mass.
• Mass is the amount of material in an object.
• Think about this would you rather push a bike or
  a car?
• It would be much harder to get a car moving due
  to its mass.
• It takes more force to move a large mass than a
  small mass.

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Newtons Laws of Motion

• 1. An object at rest remains at rest and an
  object in motion remains in motion in a straight
  line unless acted upon by a force.
• 2. When force acts on an object, the object will
  move according to the amount of force. The
  greater the mass of the object is, the smaller
  the change in motion will be.

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Newtons Laws

• 3. If an object exerts a force on a second
  object, the second object will exert an equal
  force.

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Think about it..

• If an object is standing still, are any forces
  acting upon it?

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Natural Forces Gravity

• Gravity is the pull that objects have on other
  objects around them. Earth is the largest object
  in our world, the pull of its gravity is the
  strongest that we feel, but is it really that
  strong?

If you toss a ball up, gravity pulls it back
towards the ground.
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Gravity controls.

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

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Experiment

• Reflection Questions
• Which is the heavier object?
• Which do you predict will reach the ground first
  and why?
• Did your prediction match the results?
• What did the experiment show and why?

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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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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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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.
• Weight changes on other planets and depends on
  the force of gravity.

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Another Natural Force

• Friction is a force that resists the motion of
  objects.
• Friction can slow down motion and even stop it.
• This force is always present when one surface
  touches another.
• Ex. of friction the sole of your shoes on the
  ground, brakes on a bike, and a ball rolling on
  the grass.