DAY 34

GOALS: SWBAT...

1. set up a lab experiment without being given specific instructions. 

2. measure vx data

3. determine delta x correctly

4. get the ball bearing in the cup, 1st time

5. Solve an acceleration problem using the GUESS method

WARM-UP:

1. Find/write the free-fall equation for free-fall time of an object with initial velocity zero

2. Find the free-fall time for an object with initial velocity zero and initial height of 3m

CLASSWORK

1. #034A: Pre-Lab completion 

• Work in your groups. Each person must write their answers on their own paper, which will be your "ticket" to begin the lab Thursday. If your pre-lab isn't complete and correct, you'll have to finish it instead of working on the lab with your groupmates.... 

• You need to come up with a procedure for this lab. One way to come up with a procedure is to "work backwards"

  • With that in mind, the last thing you'll do is put the cup a certain distance from the end of the table. How will you know where to put the cup?

  • HINT: The answer to the above has something to do with the time the projectile is in the air, and its horizontal velocity. 

  • With that in mind, "How will you measure vx?" And how can you calculate the time the projectile is in the air?

  • HINT: Respectively, the answers to the above have something to do distance and time, and with free-fall

• Hypothesis question: Will a ball moving in projectile motion experience a constant or changing (accelerating) horizontal (x) velocity? Explain why/why not. 

• Some things to consider today while you're answering the pre-lab questions:

  • Consider your answer to Pre-lab #1 and answer this question: Which path will your rolling projectile take when it leaves the edge of the table? (see pic on board)

  • To think about how to measure vx, consider the following. Ignoring friction, where can we assume the marble has constant velocity (there are two correct answers). Of those two places, which would be easiest to measure vx?

    • on ramp

    • on horizontal table

    • in air (free-fall)

  • Does a projectile falling straight down fall faster, slower, or at the same speed as a ball falling with horizontal velocity? Watch the video to see the answer, then use what you saw to think about how to find the time the projectile takes to hit the ground

    • Check this video to see the answer: https://www.youtube.com/watch?v=PuhxNivCKOA

  • Still struggling with #2-5? The HW video on projectile motion covers the same type of problem. Follow Mr. P through the solution for the times listed below

    • 4:29 Beginning to solve the problem.

    • 5:13 Solving for the change in time in the y-direction.

    • 6:22 Solving for the displacement in the x-direction.

    • 7:29 Video proof that it works.

    • Video LINK

2. #034B: Lab Data Collection  - Sample Procedure

This is one set of steps you can use to successfully complete the lab. 

• Make a data table with displacement and time. On your table, mark your xi and xf points with small pieces of tape - I suggest that your displacement length should be .20m - .30m, but it's up to you. You must collect constant velocity data on a FLAT SURFACE. Collect 10 trials for the time. Take the average of those ten time values to find your average time.

• Use the time and displacement to find vx.

• Measure delta y between the top of the cup and the table top (you can measure the ycup, ytabletop, and _________ the two. 

• solve the free-fall problem to determine the time to fall delta y

• Use the free-fall time and the vx you calculated to calculate delta x for your projectile motion

• Use a plumb bob to find the initial x position for your projectile motion

• measure out the location for your cup.

• When you're ready, call me over for your one attempt, and put your cup in the correct spot. Video your attempt.

Learning at Home (HW) (15min)

1. Some of you are still struggling with how to proceed for this lab

    Copy, and fill in the blanks: ()

1. After measuring ytabletop and ycup, I can _______ them, and solve for Δ___. 

2. Using the ______ equation, I can then solve for the ____ the projectile takes to fall from that height. 

3. Separately, I can set up a ramp & displacement zone, then use the time and displacement to find __________

4. Now that I know the time the ball will be in the air, and horizontal velocity, I can use that with

5. the velocity equation, vx = Δ__/Δ__  

6. I'll need to rearrange the velocity equation to solve for displacement, so it looks like...

7. Δx = __*Δ__

8. That's the displacement from the edge of the table to where I put the ___ on the floor. 

9. Done. 

2. Watch the video to review how to solve free fall problems. Make sure that in your notes, you write down the rearranged equation to solve for free-fall time with an initial velocity of zero. (hint, this shows up about four and a half minutes into the video)

LINK

3. Solve the following problem:

Find the time for a horizontally thrown 90 mile/hr ball to hit the ground, if it leaves the throwers hand at 2.00 meters above the ground. 

Follow-up question: Does the horizontal speed of the ball affect how long it takes it to fall?

Exam Review:

Link to the review is here: LINK

#Goals: SWBAT...

1. Describe which friction coefficient refers to moving objects, and which refers to objects at rest

2. Draw accurate FBD's

3. Solve problems involving kinetic and static friction

Warm-Up (5min) 

Copy and answer the following:

• 1. What is x when x+y=5 and y=-2  ?

• 2. What is x when x+y=5 and x-2y=0  ?

• 3. What is FA when FA is horizontal, Ff=+5N, and Fnet=-10N?

CLASSWORK

1. #034A: Understanding the Force of Friction Equation

Take notes: EDpuzzle

Answer the following: 

CH 5 #27: You've now learned about static and kinetic friction. How are these two types of friction similar? What are the differences between static and kinetic friction?

2. #034B: An Example of how to solve a Friction Problem, plus two Practice Problems

    A. Copy the following: Example Problem: You apply a horizontal force of 2.0 Newtons to a book with a mass of 0.674 kg, and it begins to accelerate. The values for the coefficients of friction between the book and the incline are µs = 0.27 and µk = 0.24. What is the acceleration of the book?

    Take notes as we solve

    B. Solve these two on your own: 

        CH 5 pg 128 Practice Problem #3: You push a 25.0-kg wooden box across a wooden floor at a constant speed of 1.0 m/s. Draw a FBD. How much force do you exert on the box? FYI: for wood on wood, µs = 0.50 and µk = 0.20

        CH 5 pg 128 #17: A girl exerts a 36-N horizontal force as she pulls a 52-N sled across a cement sidewalk at constant speed. Draw a FBD. What is the coefficient of kinetic friction between the sidewalk and the metal sled runners? Ignore air resistance.

At Home Learning (HW) 

1. Complete the problems from #034B

    If you're stuck on Practice Problem #3, or want to check your work, the solution is in CH 5, pg 128. Use the link to the online textbook in the margin to the left.

2. #034C: Period 1-3: Watch/take notes on the following. If you're in period 4-5, scroll down a bit...

    Understanding the Force of Friction Equation - EDpuzzle

    #034C: For period 5-6: Watch/take notes/complete edPuzzle on the following:

    Introduction to Static and Kinetic Friction by Bobby - EDpuzzle

3. #034D: Watch/take notes/complete edPuzzle on the following:

    Do Anti-lock Brakes use Static or Kinetic Friction? by Billy - EDpuzzle

Optional Review: Still confused about how to solve problems like these? Try watching the videos below. 

Coefficient of Friction

Notes: LINK

    A. Are the coefficients for static and kinetic friction the same, or different? 

    B. Is one always larger than than the other? Which one?

Summing the Forces

Does the Book Move? An Introductory Friction Problem - EDpuzzle