DAY 47

NGSS Standard (this is what we're learning with this unit)

Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship amongthe net force on a macroscopic object, its mass, and its acceleration. [Clarification Statement: Examples of data could include tables or graphs of position or velocity as a function of time for objects subject to a net unbalanced force, such as a falling object, an object sliding down a ramp, or a moving object being pulled by a constant force.] [Assessment Boundary: Assessment is limited to one-dimensional motion and to macroscopic objects moving at non-relativistic speeds.]

#Goals: SWBAT...

1. Describe the characteristics of Friction

2. Define Static and Kinetic Friction

3. Use FBD's to find Net Force and acceleration

4. Draw correct FBD's, with appropriate vector magnitude and direction.

WARM-UP (review of your Friction HW notes) (8min)

0. Do you have the textbook for this class? If no, please tell me now. 

1. What is the symbol for the force of friction?

2. Define "Static"

3. Define "Kinetic"

4. Does the amount of friction depend on surface area? (AKA, would a truck with four tires feel different friction from a truck with six tires?)

5. Does friction oppose the direction of motion?

6. Does friction oppose the direction of the force applied?

7. Is friction perpendicular to the sliding surface, or parallel to it?

8. What does a smooth surface look like under a microscope? Still smooth, or rough?

9. Which is more difficult: Getting an object moving, or keeping it moving?

10. What is the symbol for the coefficient of friction (mu) and what are it's units?

CLASSWORK

1. HW Review

2. #047A: Finding Acceleration, Fnet, or mass via FBD's

The net force is the vector sum of all the individual forces. 

In this lesson, we will learn how to determine the acceleration of an object if the magnitudes of all the individual forces are known. 

The three major equations that will be useful are 

the equation for net force (Fnet = m•a), 

the equation for gravitational force (Fg = m•g), 

and the equation for frictional force (Ff = μ • FN).   <------THIS IS NEW! :-) A really cool thing about the equation for friction is it's dependence on the normal force. Think about what happens when you try to go up a steep hill. 

    - In what direction does the gravitational force pull you?

    - In what direction does the normal force push you?

    - As a hill gets steeper, what happens to the direction of the normal force? 

The process of determining the acceleration of an object demands that the mass and the net force are known. If mass (m) and net force (Fnet) are known, then the acceleration is determined by use of the equation.

a = Fnet / m

2. 047B: Your Turn to Practice

This task involves using the above equations, the given information, and your understanding of Newton's laws to determine the acceleration. To gain a feel for how this method is applied, try the following practice problems. ALWAYS START BY SUMMING THE FORCES IN THE X and Y. AKA, Fnet x and Fnet y

Practice #1

An applied force of 50 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of friction. Use the diagram to determine the normal force, the net force, the mass, and the acceleration of the object. (Neglect air resistance.)

At Home Learning (HW) 

1. #047C: Your homework, due Wednesday, is to prepare for class by watching 10 minutes worth of video. You should understand how to solve net force and friction problems after watching the video, and doing the three practice problems. Pause the video after the teacher describes the scenario, try the problem on your own, then un-pause the video, and check to see if your solution was correct. Be sure to write the problem and solution into your notes. 

The Step-by-Step Science video is here --> LINK

2. Curious about fire preparedness? Click here: https://www.lafd.org/ready-set-go

NGSS Standard (this is what we're learning with this unit)

Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship amongthe net force on a macroscopic object, its mass, and its acceleration. [Clarification Statement: Examples of data could include tables or graphs of position or velocity as a function of time for objects subject to a net unbalanced force, such as a falling object, an object sliding down a ramp, or a moving object being pulled by a constant force.] [Assessment Boundary: Assessment is limited to one-dimensional motion and to macroscopic objects moving at non-relativistic speeds.]

#Goals: SWBAT...

1. Draw correct FBD's, with appropriate vector magnitude and direction.

2. Support classmates with helpful tutoring

3. Use FBD's to find Net Force

4. Describe the relationship between mass, net force, and acceleration

Warm-Up (4min) 

1. You apply a force to the left to push a 89g Matchbox car across the level floor. 

2. A. Draw a free body diagram showing the forces WHILE you're accelerating the car. 

3. B. Draw a free body diagram showing the forces AFTER you release the car. 

CLASSWORK

1. I'll check your HW from Day 46 on Wednesday, and we will go over it in class that day. 

2. #047A: Recognizing Forces

    Instructions: Your challenge is to identify the types of forces that act upon an object in any given situation.

    For each level

        - List the problem number. 

        - List the forces present.

        - Draw a FBD that could represent the scenario given.

    Complete the Apprentice & Master levels

    There are ten of these in total

    Ask your substitute teacher to put their signature at the end of your work/notes for the day

    Link to activity is here --> LINK

    If you need some help getting started with the classwork, here’s a short video.

http://www.youtube.com/watch?v=IElHx7F7rlM

3. If you finish early, work on the Learning at Home (HW) video (see below)

Learning at Home (HW)

Friction Edpuzzle Video: https://edpuzzle.com/media/580903379935d0833a02c646

Notes: https://www.flippingphysics.com/uploads/2/1/1/0/21103672/0126_lecture_notes_-_understanding_the_force_of_friction_equation.pdf

OLD STUFF BELOW - DISREGARD

#Goals: SWBAT...

1. Define "impulse"

2. Understand that a longer time period (larger delta t) results in a smaller force

3. Use the impulse-momentum equation to solve momentum problems. 

Warm-Up (4min):

• https://www.youtube.com/watch?v=fdeH6Ksedwk

• Recall from your HW video: Impulse is the change in momentum  (Δp). 

1. Is the impulse when the brick hits the table the same or different as the brick hitting the foam?

   1. When our video presenter jumps from the table, he begins falling. Does his momentum increase, remain constant, or decrease?

2. Does he want to experience a strong force when he lands?              Why/why not?

3. How does he protect himself upon landing?

4. Why are running shoes helpful for our feet?

CLASSWORK

1. #047A: The connection between Impulse and Momentum

• • 1. Read the first 8 paragraphs, stopping at "Representing a Rebounding Collision" (10min)

  • http://www.physicsclassroom.com/class/momentum/Lesson-1/Momentum-and-Impulse-Connection

  • key concepts:

    • • F = m • a

      • or

      • F = m • ∆v / t

        • • F • t = m • ∆v

      • If both sides of the above equation are multiplied by the quantity t, a new equation results.

• • • • • Impulse = Change in momentum

• • • • Example: Solve the practice problem with the football halfback 

2. #047B: Representing a Rebounding Collision Practice Problems

• We will solve example problem #1 together, and you'll do #2 and #3

• Impulse Momentum Chart

At Home Learning (HW) 

1. If today was confusing, I made a video showing some of the key points here: LINK1

2. 47B: Complete the impulse momentum chart, as shown at the end of the video above. Link is above in 047A

3. 47C: Take notes/answer edpuzzle questions here:

    Keep in mind that the impulse-momentum equation can be re-written to solve for the force of a collision like this: F = (m • ∆v)/t , as seen in the beginning of the video

 (7:55) Impulse Introduction or If You Don't Bend Your Knees When Stepping off a Wall - EDpuzzle