# April 23 & 24 Take back your exit slips Take a clicker

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April 23 & 24 Take back your exit slips Take a clicker
Homework Due Read & Study 10.1, 10.4, 10.6 - Do # 1-3, 8-10, p. 147 Tonight’s HW Read & Study ALL of Ch 10 – Do # 4-7, p. 147 *Expect an open notes Ch 10 quiz next class! Finish today’s POGIL if necessary  won’t be collected, but since you will have a quiz next class Do Now Take back your exit slips Take a clicker On my desk…take a Do Now and complete BOTH SIDES

Which could be a correct possible position of the CG of this demo?
Not listed 10

Let’s review the Do Now…

#1. Why does a VERY pregnant woman lean backward when walking?
To shift her CG forward, allowing her to keep CG above area of support and maintain balance To shift her CG backward, allowing her to keep CG above area of support and maintain balance To look cool

#2. Why does a hiker carrying a heavy backpack lean forward?
To shift CG forward, allowing him to keep CG above area of support and maintain balance To shift CG backward, allowing him to keep CG above area of support and maintain balance To look cool

#3 - How does a heavy tail enable a monkey standing on a branch to reach farther branches?

#4. When you carry a heavy object with one arm, like a suitcase, why do you tend to hold your free arm out horizontally? To shift your CG towards the suitcase and maintain balance To shift your CG away from the suitcase and maintain balance To look cool

#5. Why is it dangerous to roll open the top drawer of a fully loaded file cabinet that is not secured to the floor? Because the CG will be above the area of support and it will fall Because the CG will extend beyond the area of support (will no longer be above the area of support) and it will fall

#6. The CG is marked by the ‘x’. Which truck will fall over?
Truck A Truck B Truck C A & B B & C A & C All of the trucks will fall None will fall

And now, a brief recap of the concepts you should have attained by now…

Center of Mass The center of mass of an object is the point located at the object’s average position of mass.

Location of the Center of Mass
For a symmetrical object, such as a baseball, the center of mass is at the geometric center of the object. For an irregularly shaped object, such as a baseball bat, the center of mass is toward the heavier end.

Center of Mass The center of mass of the rotating wrench follows a straight-line path as it slides across a smooth surface. As an object slides across a surface, its center of mass follows a straight-line path.

Center of Mass The centers of mass of the baseball and of the spinning baseball bat each follow parabolic paths.

11.5 Torque and Center of Gravity
Items topple when the CG extends beyond its support base.

11.5 Torque and Center of Gravity
The Leaning Tower of Pisa does not topple because its CG does not extend beyond its base. A vertical line below the CG falls inside the base, and so the Leaning Tower has stood for centuries. If the tower leaned far enough that the CG extended beyond the base, it would topple.

~10 minutes DO #1-3!!! Number the paragraphs Chunk the text.
Underline and circle… with a purpose.  Left margin: What is the author SAYING? Right margin: Dig deeper into the text   by doing all this  ~10 minutes DO #1-3!!!

On to the POGIL! CHECK IN AT STOP SIGNS!
We are NOT going over as a class – PLEASE check in with a teacher as a group! Stopping with 7 minutes left for a clicker exit!!!

You should know how to… Predict whether or not an object will topple (based on whether or not the CG is aligned with the area of support) Determine what type of equilibrium an object experiences based on the location of its CG (stable, unstable, neutral)

Lowering the CG of an Object
Stability Lowering the CG of an Object The CG of an object tends to take the lowest position available.

Stability The CG of an object has a tendency to take the lowest position available. A table tennis ball is placed at the bottom of a container of dried beans.

Try this with Popcorn! Stability
The CG of an object has a tendency to take the lowest position available. A table tennis ball is placed at the bottom of a container of dried beans. When the container is shaken from side to side, the ball is nudged to the top. Try this with Popcorn!

Stability The same thing happens when an object is placed in water:
If the object weighs less than an equal volume of water, the object is forced to the surface. The CG of the whole system will be lowered because the heavier water occupies the lower space. If the object is heavier than an equal volume of water, it will be more dense than water and sink. The CG of the whole system is lowered. If the object weighs the same as an equal volume of water, the CG of the system is unchanged whether the object rises or sinks.

Stability The CG of the glass of water is affected by the position of the table tennis ball. The CG is higher when the ball is anchored to the bottom.

Stability The CG of the glass of water is affected by the position of the table tennis ball. The CG is higher when the ball is anchored to the bottom. The CG is lower when the ball floats.

Stuff tends to take the LOWEST CG = Most Stable! If the object weighs less than an equal volume of water, the object is forced to the surface. The CG of the whole system will be lowered because the heavier water occupies the lower space. If the object is heavier than an equal volume of water, it will be more dense than water and sink. The CG of the whole system is lowered. If the object weighs the same as an equal volume of water, the CG of the system is unchanged whether the object rises or sinks.

Stuff tends to take the LOWEST CG = Most Stable! If the object weighs less than an equal volume of water, the object is forced to the surface. The CG of the whole system will be lowered because the heavier water occupies the lower space. If the object is heavier than an equal volume of water, it will be more dense than water and sink. The CG of the whole system is lowered. If the object weighs the same as an equal volume of water, the CG of the system is unchanged whether the object rises or sinks.

Both of these objects are WEIGHTED towards the bottom
Both of these objects are WEIGHTED towards the bottom. Think about what that means regarding the location of the CG…. What type of equilibrium do they experience? Stable Unstable Neutral

Both of these objects are WEIGHTED towards the bottom
Both of these objects are WEIGHTED towards the bottom. They are STABLE This explains why they always right themselves!

Why doesn’t the Seattle Space Needle topple??
DISCUSS!

The Seattle Space Needle is so “deeply rooted” that its center of mass is actually below ground level. It cannot fall over intact because falling would not lower its CG at all. If the structure were to tilt intact onto the ground, its CG would be raised!

Any questions about… Any material from last class/ today?

On a scale of 1-5, how confident are you with the material from Chapter 10 so far?
I have no clue what is going on I understand a few bits and pieces, but other than that, I’m stuck Ehh..With more practice, I’ll be OK I’m OK with this – tonight’s HW and next class’ extra practice should clear up any issues for me! So confident, I could teach it to someone else!

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