Ch 9 – Day 2March 17 & 18

Homework Due

*Ch 9 #1-7 - Place in in box!***Project1. Fill out a group grade agreement.2. At the bottom, WRITE the submission method

(flash drive, emailed link, etc.)3. Staple the form to your RUBRIC & WORKS CITED4. **Place stapled work in a SEPARATE in box! **If you are handing in a flash drive / disk, ensure your FULL NAME is CLEARLY WRITTEN on it!

Tonight’s HW

Read & Study 9.3-9.4, do #8-12 p. 133 Ch 9 open notes quest on Friday. Will NOT

take up the entire class block – we will start Ch. 12 on this day, too.

Do Now Take one and complete! (Use notes from last class for formula, units, etc.)

ω = 2 / Tω = 2 / (10s) = ~0.628 RPS

vt = ωr OR = (2 / Tvt = (0.628 RPS) 3m vt = ~1.884 m/s

ω = 2 / Tω = 2 / (8s) CAREFUL!!! = ~0.785 RPM

vt = ωr OR = (2 / Tvt = (0.785 RPM) 3m vt = ~2.355 m/s

Take back yesterday’s exit slips MAKE CORRECTIONS!

ASK for help from a peer or teacher!

Answers mean NOTHING if you can’t understand the proper thought process / errors!!!!

Take out the HW due today (#1-7) Pay attention! We are rapidly

reviewing / popcorning!!!

1. See definitions. (spin vs. orbit, etc.)2. Revolves – the axis is EXTERNAL of the kid3. Linear/Tangential: circumference per time Rotational/Angular: # of spins per timeEtc.

4. Tangential (speed, velocity, etc.)5. As rotational speed increases, so does tangential speed…

DIRECTLY PROPORTIONAL!6. As RADIUS increases, so does tangential

DIRECTLY PROPORTIONAL!7. larger diameter = larger tangential speed

Watch the marble and plate demo. Then, discuss the answer to this question (with your peers…but you may find it helpful to jot down ideas in your notes):

Using Newton’s Laws as the basis for your argument, explain whether or not there must be force causing the object to move in a circle.

Newton’s 1st Law states that if there is NO net force, an object at rest will stay at rest An object in motion will stay in motion

without acceleration In other words, it will not accelerate it will

not change its velocity it will not speed up, slow down, or change direction.

Does the marble travel in a straight line?

So…does it change direction? So… does it change velocity?

In Summary…

No Yes

Yes

Newton’s 2nd Law states that IF there is a net force, an object will accelerate

In other words it will change its velocity it will speed up, slow down, change direction or any combination of the 3.

Does the marble travel in a straight line? So…does it change direction? So… does it accelerate? So… is there a force that causes this acceleration?

Your goal is to figure out what direction this force acts (and therefore, what direction the acceleration acts, since the acceleration is in the same direction as the net force)

In Summary…

No Yes

YesYes

Newton’s 2nd Law states that IF there is a net force, an object will accelerate

In other words it will change its velocity it will speed up, slow down, change direction or any combination of the 3.

Does the marble travel in a straight line? So…does it change direction? So… does it accelerate? So… is there a force that causes this acceleration?

Your goal is to figure out what direction this force acts (and therefore, what direction the acceleration acts, since the acceleration is in the same direction as the net force)

In Summary…

No Yes

YesYes

Centripetal Force Means “center seeking” or

“towards the center” Any force that causes an

object to follow a circular path. EXAMPLE: The force that holds

the occupants in a rotating ride.

Name give to any force that is directed at a right angle to the path of a moving object and that tends to produce circular motion

If the centripetal force is removed, an object will follow a straight line, TANGENTIAL path (like in the plate & marble, and hula hoop demo!)

Centrifugal Force

It is NOT real force because it is NOT part of an action-reaction pair!

Misconception that centrifugal force pulls you outward during circular motion. THERE IS NO FORCE PULLING YOU OUTWARD! Actually, it is just the inertia of the

body traveling tangent to the circle.

• Means “center fleeing,” or “away from the center”• The Physics F-WORD!!!! F is for fake, false,

fabricated, fictitious, forbidden, etc…• Very commonly misused. – (people say centrifugal when they should say centripetal)

As a ball is whirled above the head, it is the inertia of the ball that wants to continue moving in a straight line. Instead, the ball is forced inward to change its direction (Centripetal Force-supplied by string).

• Inward Force• Inward acceleration• Tangent velocity

Exit Slip *Complete and turn in!!!

Tonight’s HW

Read & Study 9.3-9.4, do #8-12 p. 133

Ch 9 open notes quest on Friday. Quest will NOT take up the entire

class block – we will start Ch. 12 on this day, too.

The STUDY GUIDE for the quest is online – stop by tomorrow for a hard copy, or I will give you a hard copy in class on Wednesday!