DAY 43
#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
Warm-Up (4min)
Copy and answer the following:
1. What is the equation which represents Newton's 2nd Law of Motion?
2. What mathematical operation does Σ represent?
3. What are the units of a Newton?
4. Draw a free body diagram representing a book, sliding to the right on a horizontal table, with applied force of +10.0N, and friction of -4.5N.
CLASSWORK
1. Tutoring: Modeling and Practice
We're going to continue to help each other. From yesterday, here's our list of best tutoring practices:
Don't give student the answer
let student think on their own
ask guiding questions
guide student to figure out mistakes
be nice, calm, patient, supportive
try to make student solve problem
review the topic (this is a great way to guide students thru finding their mistake)
give a person a fish vs. teach a person to fish
2. #043A: Practice Problems
A book is at rest on a tabletop. Diagram the forces acting on the book.
A gymnast holding onto a bar, is suspended motionless in mid-air. The bar is supported by two ropes that attach to the ceiling. Diagram the forces acting on the combination of gymnast and bar.
An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it is falling.
A flying squirrel is gliding straight down (no flapping of the wings) from a tree to the ground at constant velocity. Consider air resistance. Diagram the forces acting on the squirrel.
A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book.
A rightward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book.
A college student rests a backpack upon his shoulder. The pack is suspended motionless by one strap from one shoulder. Diagram the vertical forces acting on the backpack.
A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver.
A force is applied to the right to drag a sled across loosely packed snow with a rightward acceleration. Neglect air resistance. Diagram the forces acting upon the sled.
A football is moving upwards towards its peak after having been booted by the punter. Neglect air resistance. Diagram the forces acting upon the football as it rises upward towards its peak.
A car is coasting to the right and slowing down. Neglect air resistance. Diagram the forces acting upon the car
Need the answers to #043A? There is a video posted HERE with solutions, but LAUSD has blocked it. Toooooo much learning <shrug>. You can also check your answers HERE
3. #043B: Determining the Net Force & Acceleration using Newton's 2nd Law
Notes:
Newton's 2nd Law: The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
If either all the vertical forces (up and down) do not cancel each other and/or all horizontal forces do not cancel each other, then an unbalanced force exists.
Review the following. Are the forces balanced?
If the forces are unbalanced, a NET FORCE exists
What is the net force in each of the above?
So what? Well, a net force causes acceleration, and we can use that fact to solve problems.
Practice:
Try solving for the acceleration of the three objects shown above. The mass for each object is 10kg. Remember that acceleration is a vector, so you'll need magnitude and direction of a for your answer.
At Home Learning (HW)
1. Friday we will take a two question FBD quiz. Prepare yourself. Review notes, videos, and practice problems from Day 42 & 43 & 44.
2. #043C: Your homework, due Thursday, is to prepare for class by watching 8.5 minutes worth of video. You should understand how to solve net force problems after watching the video
Take Notes: Introductory Newton's 2nd Law Example Problem
Watch the video, and answer the EdPuzzle Questions: EDpuzzle
NGSS Standard
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 Fg and FN vectors.
2. Say when forces are balanced and when they aren't balanced.
3. Draw correct FBD's, with appropriate vector magnitude and direction.
4. Support classmates with helpful tutoring
Warm-Up (4min)
Copy and fill in (or choose) the correct answers for the following:
1. FBD stands for _____ ______ ______
2. The size of the vector arrow in a FBD represents the _________ of the force.
3. In which direction does the force of gravity ALWAYS work?
4. If forces are unbalanced, the velocity be (constant/accelerating).
5. Draw both FBD's. Which FBD on the board is correct? Why is the other one incorrect? (Hint: There's only one thing wrong)
CLASSWORK
1. #043A: Review of How-To Draw Free Body Diagrams (FBD's) (5min)
Notes:FBD's show magnitude and direction of all forces acting upon an object.
Vector size represents the magnitude of the force.
Vector direction shows the direction the force is acting.
Each vector needs a label
The object is represented by a box and the force vector is drawn from the center of the box outward in the direction that the force is acting. An example of a free-body diagram is shown at the right.
2. #043B: Process for Drawing a FBD (3min)
When given a description of a physical situation, identify which forces are present.
Determine the direction in which each force is acting.
Draw a box and add vectors for each existing force in the appropriate direction
Label each force vector according to its type
3. #043C: Modeling and Practice
Learning at Home (HW)
1. #043D: Your homework, due Thursday, is to prepare for class by watching 9.5 minutes worth of video. You should understand how to solve net force problems after watching the video. You should also know what this symbol ∑ means...
Watch the video, and answer the EdPuzzle Questions: EDpuzzle
2. Complete Ball in a Cup Lab, due Wednesday @ 11:59pm, submitted electronically via the pre-lab document (which you already shared with me). Note, there is no hypothesis this time
This should include the following.
TITLE Ball in a Cup Lab
NAMES & GROUP MEMBERS NAMES
PURPOSE
set of instructions
MATERIALS
list them
PROCEDURE
this should be a list of instructions specific/detailed enough that another person could read them, and do the lab correctly.
DATA
small chart of time data for finding Vx
free-fall time calculation for finding Δt
calculation showing how you found Δx for the cup
***note that you can take a photo of your neat math work showing the above
SAMPLE CALCULATIONS should be included in the DATA section, or immediately following the DATA section
show how you did all the math leading up to, and including, solving Δx=vixΔt
RESULTS
what happened? (where did the ball land? Using your video, you can take a screenshot of the ball landing in the cup (or missing) and upload it to your document).
ANALYSIS
- Any errors? You'll need to be specific when discussing errors. For example:
- state where in an equation you made a mistake, and how that mistake affected your results
- describe a physical error (mistiming the displacement zone for vx, releasing the ball from too high/too low, tilted table, wrong angle for ramp, etc), and state how it/they affected your results.
- If you didn't have any errors, why not? What steps did you take that made your lab work so well?
CONCLUSION
- Sum up the lab - describe if you were/weren't successful. What might you do differently next time to be more successful?
If you'd like to use the template and see the rubric, here they are again
Grading Rubric LINK
Lab Template: LINK
#Goals: SWBAT...
1. Categorize forces as internal or external
2. Understand how internal vs. external forces affect the TME
2. Answer medium difficulty energy problems with conservative and non-conservative forces
NOT CHECKING HW TODAY. WILL CHECK THE EXTRA CREDIT IF YOU HAVE IT DONE. JUST COME UP. LAST DAY FOR THIS EXTRA CREDIT IS MONDAY
Warm-Up (4min): Internal vs. External Forces/PE vs. KE/ + - Work
Does physics make happy?
A tennis ball with a mass of 58 grams is launched from a trebuchet with an initial speed of 6.8 m/s and an initial height of 1.3 meters. Assume level ground, and no air resistance (friction). Consider the system to just be the ball. Does the trebuchet apply an internal or external force on the ball?
Considering only the flight (after launch, before impact with the ground) is energy conserved?
The Trebuchet converts PE to KE to launch the ball. After the ball is launched, how does the ball's KE change?
Does the trebuchet do positive or negative work on the ball?
CLASSWORK
1. #043A: "Introductory Conservation of Mechanical Energy Problem using a Trebuchet" Notes
Introductory Conservation of Mechanical Energy Problem using a Trebuchet - EDpuzzle
2. 043B: Relating Work from External Forces to TME
Whenever work is done upon an object by an external force, there will be a change in the total mechanical energy of the object (energy not conserved).
If forces are only internal, energy is conserved
The relationship between work and mechanical energy is expressed by the following equation:
TMEi + Wext = TMEf
The equation states that the initial amount of total mechanical energy (TMEi) plus the work done by external forces (Wext) is equal to the final amount of total mechanical energy (TMEf). A few notes should be made about the above equation. First, the mechanical energy can be either potential energy (in which case it could be due to springs or gravity) or kinetic energy. Given this fact, the above equation can be rewritten as
KEi + PEi + Wext = KEf + PEf
3. #043C: Examples and Practice Problems
4. Quiz grading
At Home Learning (HW)
1. Monday we'll be solving some pretty complex TME problems. Complete the three practice problems from 043C, which we began in class, as well as the stopping distance activity immediately below it.
2. #043D: TME Practice with Flipping Physics: Watch/take notes/complete edpuzzle questions on the following: