Unit 5 Constant Force Particle Model

Unit 5 transition lab

Talk about the max and the force for moving at a constant speed before

What are the factors you could change that might affect the friction between the block and the table?

Unit 5 Paradigm lab

What are the factors you can change that might affect the acceleration of the cart?

Force

Pull angle

Mass/weight

Ramp angle

We did the lab with mass vs acceleration and found it difficult to get accurate data with the spring scale.  There was a good interaction with the instructor as we thought it looked linear with a negative slope.  We were directed to think about the significance of the intercepts.  We ran another point and found a good inverse fit.

Here is some of the questions during board meeting

• ·         Lets start with varying force
• ·         How did you do it—we put extra mass on the car and it made it easier to keep up with the car
• ·         Make sure you write down the things that were kept constant—do it on your boards now.
• ·         Why did you load the car up with a bunch of mass?
• ·         Do we see a proportional increase?
• ·         Do the data tables bear that out?  Looking at different intervals in the data table comparing with different models
• ·         You have to convince us, does your data table help with that?
• ·         Where is your intercept?  What does 0, 0 mean in your graph.
• ·         If we say its linear then if we multiply the x by 2 what happens to the y.
• ·         If it is linear we should have a for every statement, what is your for every statement.
• ·         Why do you have different slopes?
• ·         Write on the board—graph of accel and force as a straight line. a=( ) F
• ·         Let’s look at the mass vs acceleration board someone points out that one group had added mass instead of total mass.
• I don’t want to write on the board unless you are confident.
• Just because I’m writing on the board doesn't mean its correct. We may need to adjust it. (Teacher mode Sometimes I leave something hanging, keep track of what you leave and when you need to circle back) There is a procedure for that.
• ·         Look at the angle of pull—questions focus on the unbalanced force and the force causing the acceleration.  Draw a force diagram for a 60 degree pole.  Discuss.  Then draw a critical competitor.  How does that compare to what we saw from the acceleration – force plot.

A general rule is not to put units in the equation but when you are naming the coefficient.  

Relate these together.

Assignment try to find coeff3.  The assumption is the pulling force is the unbalanced force.  This is a big moment.  We used “the google” to verify our response

The force is the cause and the acceleration is the result.  a=F/m  The process is what is important.

So if we are given the forces, we can find the unbalanced force and then find the acceleration.

Also note that the unbalanced force and the acceleration are in the same direction.

We work on Unit 5 worksheet 1 and then practicum of elevator work.

Is there a value for a freely accelerating object.

We have dealt with being careful of terms quite a bit like "Falling faster?  Seems to denote velocity. Analyzing graphs from dropping a ball.

Get away from freefall acceleration because it denotes going down.

Bathroom scale measures the force between you and the scale.

Elevator activity

Discussion of when you feel heavy and light.  Does your weight change?  What is true of the acceleration?

Lead to weightless discussion.  What if the floor doesn't push you up anymore?

Block sitting on the table name two forces acting on the object.  Are they Newton’s third law force pairs?

Extras Make a list of questions and misconceptions Give seeds and prompts as you walk around

Aron’s article chapter 3  Operational definition of mass

Day 10

Begin talking about Arons 3.10-3.20.  Got into a discussion of newton’s 3^rd law equal but opposite terms

Cart on track with small weight

You have the tools to find the acceleration of the cart.

1^st step draw the system schema

How many interactions are there on the mass?  2  so the force diagram should have 2 arrows

Is the earth force bigger or smaller than the force of the earth.

Can we predict the acceleration of the cart mathematically

Let’s look at the system.  What stuff matters. 

Greg asked a question.  It was becoming a dialog between Don and Greg and so then he had us discuss it among ourselves to try and get into Greg’s head and describe what he is saying.  A chance to bring it back to the whole class instead of a 2 person discussion

System—stuff that matters  Draw a dotty line around the stuff that matters.

The intuitive leap—What does the pulley do it rotates the string 90 degrees clockwise  What if we undid that  Can the two string forces be the same?  Can the earth then be the unbalanced force

The unbalanced force is the weight of the object but it accelerates the whole thing mass and cart.

White board and find the acceleration of the cart

Now do the atwoods machine (named after mr. machine)

New system box being pulled by a person .  What forces are acting there is some friction but he is accelerating to the right.  How do you know where to hold the flashlight?

Kates rule the flash lights are oriented perpendicular and parallel to the surface.

Block on a ramp—only do this for advanced classes.Drawing horizontal and vertical doesn’t help because we need a force in the direction of a and funbal.  Should I put the flashlight on the surface force?  Doesn’t cast a shadow.  So shadow the earth force.

I felt pretty good about this unit and I think it will go well.  There were a lot of aspects about force that I haven't been spending time on that I will focus on more and I think as I get into more complex problems some of those early preconceptions will be dealt with and so things will go smoother.  I think the schema will be very effective in helping the students identify what to put in their force diagrams.  As before I think limited lab stations could pose a problem that I will have to attempt to find a solution for.  One way that I will probably implement this that is a little different is that I think I will use F's for forces but subscript them with the object applying the force.

Extras covered during this unit

Video on math Dan Meyer  “Patient problem solvers”

1. lack of initiative

2. lack of perseverance

3. Lack of retention . . .

Impatient with irresolution—the math serves the conversation not the conversation the math.

Video on Kahn academy by veritasium videos will only reinforce what you believe unless misconceptions are dealt with

Video  by xted frank Noschese on modeling