DAY 26

#Goals: SWBAT...

1. Draw correct F_g and F_N 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. #026A: 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. #026B: Process for Drawing a FBD (3min)

1. When given a description of a physical situation, identify which forces are present.
2. Determine the direction in which each force is acting.
3. Draw a box and add vectors for each existing force in the appropriate direction
4. Label each force vector according to its type

3. #026C: Modeling and Practice

• Get into your lab groups
• Two examples as a class (1 and 2) (4 min)
  • Are Forces balanced or unbalanced? (check for understanding via handraise for #2)
• Assessment: So far, how well do you understand FBD's? Answer 3-5. (6min)
• We're going to help each other. What are the best ways to help a person learn via tutoring? (5 min)
  • The Way ---> https://www.youtube.com/watch?v=uLKXBHZemXQ
  • Let's make a list of the best tutoring practices:
    • As a tutor, you should...
    • made student correct themself
    • didn't say answer
    • patient, nice
    • try to make student solve problem
    • never said student was wrong
    • never told student the answer
    • reviewed the topic
    • nice, calm, patient, supportive
    • calm, patient
    • never gave the answer, made student work for it
    • guide student to figure out mistakes
    • give a person a fish vs. teach a person to fish
• If you missed two or three of problems 3-5, seek out someone in your group to provide peer tutoring. Tutors, follow the practices we just listed, and work with your classmate(s) as needed to solve 6-8. (9 min)

1. A book is at rest on a tabletop. Diagram the forces acting on the book.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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.
8. A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver.
   2. <Save the scenarios below for tomorrow>
9. 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.
11. 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.
13. A car is coasting to the right and slowing down. Neglect air resistance. Diagram the forces acting upon the car.

4. Check for understanding

1. An object sliding to the left on this inclined plane will have how many forces? (show with your fingers)

2. Raise your hand if you think the normal force won't be vertical.