More Forces and Free Body Diagrams

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More Forces and Free Body Diagrams

• Physics 11

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More forces

• Meet the Forces Handout!
• Add symbols
• Add Applied force
• Usually a push or pull (which generally look the
  same on a FBD)

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Free-body diagrams

• Free-body diagrams are used to show the relative
  magnitude and direction of all forces acting on
  an object.

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Free-body diagrams (FBDs)

• Represent all forces acting on one object and
  only the forces on the object.
• The forces that this object exerts on other
  objects are not included.
• If there is more then one object involved, each
  object needs its own FBD.
• Object drawn as a box or dot, forces indicated
  with arrows

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• This diagram shows four forces acting upon an
  object. There arent always four forces.
• For example, there could be one, two, or three
  forces.

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Create a free body diagram (FBD) for each of the
following situations. Draw a FBD of the gorilla
Free Body Diagram of the Sitting Gorilla (The box
represents the gorilla, W weight of the
gorilla, N Normal force)
Sitting Gorilla
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Force/Free Body Diagrams
Draw a FBD of the wooden swing
Parrot on wooden swing hung by ropes
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Force/Free Body Diagrams
Draw a FBD of bucket the bungee jumper leaped
from
Free Body Diagram of the bucket (T represents the
tensile force of the cable the bucket is
suspended from, and W is the weight of the diver
and the bucket)
Bungee jumping from crane
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Problem 1

• A book is at rest on a table top. Diagram the
  forces acting on the book.

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Problem 1

• In this diagram, there are normal and
  gravitational forces on the book.

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Problem 2

• An egg is free-falling from a nest in a tree.
  Neglect air resistance. Draw a free-body diagram
  showing the forces involved.

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• Gravity is the only force acting on the egg as it
  falls.

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Problem 3

• A flying squirrel is gliding (no wing flaps) from
  a tree to the ground at constant velocity.
  Consider air resistance. A free body diagram for
  this situation looks like

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• Gravity pulls down on the squirrel while air
  resistance keeps the squirrel in the air for a
  while.

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Problem 4

• A rightward force is applied to a book in order
  to move it across a desk. Consider frictional
  forces. Neglect air resistance. Construct a
  free-body diagram. Lets see what this one looks
  like.

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• Note the applied force arrow pointing to the
  right. Notice how friction force points in the
  opposite direction. Finally, there is still
  gravity and normal forces involved.

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Problem 5

• A skydiver is descending with a constant
  velocity. Consider air resistance. Draw a
  free-body diagram.

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• Gravity pulls down on the skydiver, while air
  resistance pushes up as she falls.

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Problem 6

• A football is moving upwards toward its peak
  after having been booted by the punter (ignore
  air resistance). Draw a free-body diagram.

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• The force of gravity is the only force described.
  It is not a windy day (no air resistance).

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Problem 7

• A car runs out of gas and is coasting down a
  hill.

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• Draw on board with incline.

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• Even though the car is coasting down the hill,
  there is still the dragging friction of the road
  (left pointing arrow) as well as gravity and
  normal forces.

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Practice

• Pg 148 12-15
• Free Body Diagram Sheet