DAY 37

I'M SICK. Please be quiet and focused today.

#Goals: SWBAT...

1. Define Work

2. List the requirements for a movement to be considered "work"

3. Determine if a scenario represents work

4. Solve work problems

Warm-Up (5min)

Copy the drawing from the board, then answer the questions listed here. Keep in mind that some of these could be a *tie*

• 1. Displacement: Rank the displacement (distance the car travels) from shortest to longest
• 2. Force: Rank the force required to move the car at a constant velocity from lowest to highest
• 3. Energy: Rank the energy required to move the car from the bottom to the top of the mountain from least to highest

CLASSWORK

1. #037A: NOTES: Work Definition & Equation

Background: Newton's laws serve as a useful model for analyzing motion and making predictions about the final state of an object's motion. In this unit, an entirely different model will be used to analyze the motion of objects. Motion will be approached from the perspective of work and energy. The effect that work has upon the energy of an object (or system of objects) will be investigated; the resulting velocity and/or height of the object can then be predicted from energy information.

With that, over the next few days we will learn about work, power, kinetic energy, and potential energy

Definition: Work is done upon an object when a force acts upon the object to cause a displacement of the object.

Scenarios: (are these work?)

1. A teacher applies a force to a wall and becomes exhausted.

2. A book falls off a table and free falls to the ground.

3. A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. (Careful! This is a very difficult question that will be discussed in more detail later.)

4. A rocket accelerates through space.

Mathematically, work can be expressed by the following equation.

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.

• 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.