#Goals: SWBAT...
1. use the cosine function to find components of a vector
2. Define Work
3. List the requirements for a movement to be considered "work"
4. Determine if a scenario represents work
Warm-Up (5min)
On Board
058A: WORK NOTES
Work Definition: Work is done upon an object when a force acts upon the object to cause a displacement of the object. Work is the product of force and displacement. A force is said to do work if, when acting, there is a movement of the object in the direction of the force. Work transfers energy from one place to another, or one form to another.
Work EQUATION: Mathematically, work can be expressed by the following equation. When the force
is constant and the angle between the force and the displacement d is θ, then the work done is given by W = Fd cos θ.
W = F • d • cos Θ
where F is the force, d is the displacement, and the angle (theta) is defined as the angle between the force and the displacement vector. The angle measure is defined as the angle between the force and the displacement.
Work is a SCALAR
UNIT: The SI unit of work is the joule (J). What's a Joule? Click that link. Or read this. Or both. Since work transfers energy, it's unit is the unit of energy, the Joule. From the Work equation, a Joule is a force multiplied by a displacement - the unit of force is the N, the unit of displacement is the m, so a Joule is a Nm.
Scenario A: A force acts rightward upon an object as it is displaced rightward. In such an instance, the force vector and the displacement vector are in the same direction. Thus, the angle between F and d is 0 degrees.
Scenario B: A force acts leftward upon an object that is displaced rightward. In such an instance, the force vector and the displacement vector are in the opposite direction. Thus, the angle between F and d is 180 degrees.
Scenario C: A force acts upward on an object as it is displaced rightward. In such an instance, the force vector and the displacement vector are at right angles to each other. Thus, the angle between F and d is 90 degrees.
Three key parts to work:
force
displacement
cause
To Do Work, Forces Must Cause Displacements
Let's consider Scenario C above in more detail. Scenario C involves a situation similar to the waiter who carried a tray full of meals above his head by one arm straight across the room at constant speed. It was mentioned earlier that the waiter does not do work upon the tray as he carries it across the room. The force supplied by the waiter on the tray is an upward force and the displacement of the tray is a horizontal displacement. As such, the angle between the force and the displacement is 90 degrees. If the work done by the waiter on the tray were to be calculated, then the results would be 0. Regardless of the magnitude of the force and displacement, F*d*cosine 90 degrees is 0 (since the cosine of 90 degrees is 0). A vertical force can never cause a horizontal displacement; thus, a vertical force does not do work on a horizontally displaced object!!
It can be accurately noted that the waiter's hand did push forward on the tray for a brief period of time to accelerate it from rest to a final walking speed. But once up to speed, the tray will stay in its straight-line motion at a constant speed without a forward force.
Let's consider the force of a chain pulling upwards and rightwards upon Fido in order to drag Fido to the right. It is only the horizontal component of the tension force in the chain that causes Fido to be displaced to the right. The horizontal component is found by multiplying the force F by the cosine of the angle between F and d. In this sense, the cosine theta in the work equation relates to the cause factor - it selects the portion of the force that actually causes a displacement.
2. 058B: HW Review
A. (2:57) Notes: Everybody Brought Mass to the Party! - Video: EDpuzzle
B. (7:10) Notes Introduction to Work with Examples - Video: EDpuzzle
C. Introductory Work Problem with a Shopping Cart
Edpuzzle: https://edpuzzle.com/media/5824d3f752251eea3e26cda4
3. 058C: Work Interactive
Question: What would require the most work and energy: driving a car up a gently-sloped hill or driving a car up a steep hill to the same summit? Find out the answer with the It's All Uphill Interactive.
Complete the chart with the mass of your choice, and answer all questions
Handout (in case you're absent): https://www.physicsclassroom.com/Physics-Interactives/Work-and-Energy/Its-All-Uphill/Its-All-Uphill-Exercise
Learning at Home (HW)
1. Complete 058C. Due at beginning of class Friday
Need help with the second page of the handout? http://www.youtube.com/watch?v=_4XHk8FM8Kw
Want help but don't want to hear the sound of my voice? https://www.youtube.com/watch?v=PYQWNxSOAa4
2. Watch any of the videos you've missed
A. (2:57) Notes: Everybody Brought Mass to the Party! - Video: EDpuzzle
B. (7:10) Notes Introduction to Work with Examples - Video: EDpuzzle
C. Introductory Work Problem with a Shopping Cart
Edpuzzle: https://edpuzzle.com/media/5824d3f752251eea3e26cda4
Goal:
Score 80% or higher on the exam
Introduce the concept of "Work"
Warm-Up:
none
Classwork
Exam
Learning at Home (HW)
Watch/take notes/complete edPuzzle on the following:
A. (2:57) Notes: Everybody Brought Mass to the Party! - Video: EDpuzzle
B. (7:10) Notes Introduction to Work with Examples - Video: EDpuzzle
Unit Goals:What is a wave? How do they act? How are do waves differ?
Goals: SWBAT...
1. Discuss waves’ properties using common vocabulary and they will be able to predict the behavior of waves through varying medium and at reflective endpoints
Warm-Up (5min):
1. Copy the image of the wave from the board.
2. Define the term, "wave"
3. Write a list of characteristics that you could use to describe the physical qualities of a wave. Describe each characteristic in words that any person could understand. Leave some writing space for characteristics that you might think of later during the activity
CLASSWORK
1. #058A: What is a wave
Definition: "disturbances in the space-time continuum"
aka, a movement (space) that takes time
2. #058B: Pre-test: waves
https://www.youtube.com/watch?v=lTHgiC60ajE
3. #058C: Waves on a String
We will be using an exciting new simulation, called PhET. Here's an intro to PhET: https://phet.colorado.edu/en/about
Directions:
1. Open Waves on a String, investigate wave behavior using the simulation for four minutes.
LINK --> https://phet.colorado.edu/en/simulation/wave-on-a-string
As you look at the waves’ behavior, talk with your groupmates about some reasons the waves might act the way they do.
2. Consider the list of characteristics you wrote in the warm-up. Do you see any of those characteristics present in the sim?
3. With the Oscillate button on and with No End checked, investigate waves more carefully using the Amplitude slider.
Write answers to the following after your group has talked about each and agreed.
a) Define Amplitude in everyday language.
b) Explain how the wave behaves as the Amplitude changes using the characteristics you described in the warm-up
c) Use a rope/string/ on the floor for some investigations and explain how you could change the Amplitude of a wave.
At Home Learning (HW)
1. Complete #058C part 3 (Oscillate) a, b, & c.
2. Tomorrow, I'll also be checking warm-ups (Day 49-56) for those who didn't show them to me on Friday, and the weekend video homework from Day 57.