DAY 46
NGSS Standard (this is what we're learning with this unit)
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 FBD's, with appropriate vector magnitude and direction.
2. Support classmates with helpful tutoring
3. Describe the two quantities upon which the friction force depends.
Warm-Up (4min)
You apply a force to the left to push a 89g Matchbox car across the level floor.
A. Draw a free body diagram showing the forces WHILE you're accelerating the car.
B. Draw a free body diagram showing the forces AFTER you release the car.
CLASSWORK
1. 046A: Recognizing Forces
Instructions: Your challenge is to identify the types of forces that act upon an object in any given situation.
For each level
- List the problem number.
- List the forces present.
- Draw a FBD that could represent the scenario given.
Complete the Apprentice & Master levels
There are ten of these in total
Ask your substitute teacher to put their signature at the end of your work/notes for the day
Link to activity is here --> LINK
If you need some help getting started with the classwork, here’s a short video.
http://www.youtube.com/watch?v=IElHx7F7rlM
2. 046B: Friction Equation Notes
Friction Edpuzzle Video: https://edpuzzle.com/media/580903379935d0833a02c646
Learning at Home (HW)
046C: Take notes, and answer the edpuzzle questions for the following two videos
Introduction to Static & Kinetic Friction by Bobby (4:04)
Introduction to the Coefficient of Friction (4:59)
NGSS Standard (this is what we're learning with this unit)
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 FBD's, with appropriate vector magnitude and direction.
2. Support classmates with helpful tutoring
3. Use FBD's to find Net Force
4. Describe the relationship between mass, net force, and acceleration
Warm-Up (4min)
read the scenario below, then answer the questions at the end
Two students are discussing their physics homework prior to class. They are discussing an object that is being acted upon by two individual forces (both in a vertical direction); the free-body diagram for the particular object is shown at the right. During the discussion, Anna Litical suggests to Noah Formula that the object under discussion could be moving. In fact, Anna suggests that if friction and air resistance could be ignored (because of their negligible size), the object could be moving in a horizontal direction. According to Anna, an object experiencing forces as described at the right could be experiencing a horizontal motion as described below in a dot diagram
Noah Formula objects, arguing that the object could not have any horizontal motion if there are only vertical forces acting upon it. Noah claims that the object must be at rest, perhaps on a table or floor. After all, says Noah, an object experiencing a balance of forces will be at rest. Who do you agree with? WHY?
CLASSWORK
1. #046A: Quiz #6: FBD's
2. Review the HW
What is force?
3. #046B: Relationship between F, m, and a
Complete the chart on the left board. You should be able to find one pattern for each of the three sections
4. #046C: Complete the following practice problems: (15min)
0. Example: If an object is falling straight down, the Fair is 15N, the Fg is 20N, and the mass is 5kg, what is the acceleration?
1. Determine the accelerations that result when a 12N net force is applied to a 3kg object and then to a 6kg object.
2. A net force of 15N is exerted on an encyclopedia to cause it to accelerate at a rate of 5 m/s2. Determine the mass of the encyclopedia.
3. Suppose that a sled is accelerating at a rate of 2m/s2. If the net force is tripled and the mass is doubled, then what is the new acceleration of the sled?
4. Suppose that a sled is accelerating at a rate of 2m/s2. If the net force is tripled and the mass is halved, then what is the new acceleration of the sled?
Need help? Click below...scroll down until you see the problems, then click the "see answer link"
At Home Learning (HW)
Finding Acceleration via FBD's is what we'll cover Tuesday. We will solve problems involving friction.
Do all surfaces provide the same friction? What provides the most? The least?
#046D: Take notes, and answer the edpuzzle questions for the following two videos
Introduction to Static & Kinetic Friction by Bobby (4:04)
Introduction to the Coefficient of Friction (4:59)
4. Finding Acceleration via FBD's
The net force is the vector sum of all the individual forces.
In this lesson, we will learn how to determine the acceleration of an object if the magnitudes of all the individual forces are known.
The three major equations that will be useful are
the equation for net force (Fnet = m•a),
the equation for gravitational force (Fg = m•g),
and the equation for frictional force (Ff = μ • FN). <------THIS IS NEW! :-)
The process of determining the acceleration of an object demands that the mass and the net force are known. If mass (m) and net force (Fnet) are known, then the acceleration is determined by use of the equation.
a = Fnet / m
Your Turn to Practice
Thus, the task involves using the above equations, the given information, and your understanding of Newton's laws to determine the acceleration. To gain a feel for how this method is applied, try the following practice problems. ALWAYS START BY SUMMING THE FORCES IN THE X and Y.
Practice #1
An applied force of 50 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of friction. Use the diagram to determine the normal force, the net force, the mass, and the acceleration of the object. (Neglect air resistance.)
Practice #2
An applied force of 20 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of friction. Use the diagram to determine the normal force, the net force, the coefficient of friction (μ) between the object and the surface, the mass, and the acceleration of the object. (Neglect air resistance.)
Practice #3
A 5-kg object is sliding to the right and encountering a friction force that slows it down. The coefficient of friction (μ) between the object and the surface is 0.1. Determine the force of gravity, the normal force, the force of friction, the net force, and the acceleration. (Neglect air resistance.)
#029C:
1. Edwardo applies a 4.25-N rightward force to a 0.765-kg book to accelerate it across a tabletop. The coefficient of friction between the book and the tabletop is 0.410. Determine the acceleration of the book.
2. In a physics lab, Kate and Rob use a hanging mass and pulley system to exert a 2.45 N rightward force on a 0.500-kg cart to accelerate it across a low-friction track. If the total resistance force to the motion of the cart is 0.72 N, then what is the cart's acceleration?
At Home Learning (HW)
1. Complete the problems from 29B & 29C, due Tuesday. Need help? The answers to all five problems are here: http://www.physicsclassroom.com/class/newtlaws/Lesson-3/Finding-Acceleration
2. #029D: Your homework, due Tuesday, is to prepare for class by watching 6 minutes worth of video. You should understand how to solve net force and friction problems after watching the video, and doing the practice problem. Be sure to copy the problem and solution into your notes.
Watch the video, and answer the EdPuzzle Questions: EDpuzzle
If you need an example of what the notes could/should look like, that's here: (5:59) Using Newton's Second Law to find the Force of Friction
Happy Pi Day
RIP Stephen Hawking
#Goals: SWBAT...
1. Define momentum
2. Solve basic momentum problems.
3. Create a table of friends
WARM-UP & HW Check:
A. What is the meaning of Δv? What about Δt? Δp?
B. Imagine a Big Rig hits a Prius. Who wins? Does the velocity of the Prius and/or Big Rig matter? Does the mass of the Prius and/or Big Rig matter?
C. Imagine that when they impact, the Big Rig is going North at 50mph, and the Prius is going South at 50mph. The two vehicles stick together after the collision. Which way will the stuck vehicles travel? Are you sure? How can you be so sure???
D. If you haven't yet, find the formula and definition for Momentum
CLASSWORK:
#046A: Momentum Notes
"Going into the all-star break, the Lakers are gaining momentum!" What does that mean? Think-Pair-Share
Momentum Definition: mass in motion
Symbol: p
Equation: Momentum = mass • velocity
Vector? YES
Example: Consider a 0.5-kg physics cart loaded with one 0.5-kg brick and moving with a speed of 2.0 m/s. The total mass of loaded cart is 1.0 kg and its momentum is 2.0 kg•m/s. If the cart was instead loaded with three 0.5-kg bricks, then the total mass of the loaded cart would be 2.0 kg and its momentum would be 4.0 kg•m/s. A doubling of the mass results in a doubling of the momentum.
What is the relationship between mass and momentum? Direct (linear) or inverse?
Basic Practice Problems
Your brother’s mass is 35.6 kg, and he has a 1.3-kg skateboard. What is the combined momentum of your brother and his skateboard if they are moving at 9.50 m/s?
Determine the momentum of a ...
a. 60-kg halfback moving eastward at 9 m/s.
b. 1000-kg car moving northward at 20 m/s.
c. 40-kg freshman moving southward at 2 m/s.
A car possesses 20 000 units of momentum. What would be the car's new momentum if ...
a. its velocity was doubled.
b. its velocity was tripled.
c. its mass was doubled (by adding more passengers and a greater load)
d. both its velocity was doubled and its mass was doubled.
#046B: Table of Friends
Today, you will make a Table of Friends. This is an equation sheet which you can use on any quiz or exam. It can only have (at max) symbol, equation, units, quantity measured, key words.
You should bring it to class everyday, as we will add to it
PERIOD 6: FIRE EXTINGUISHER
Learning at home
Complete your Table of Friends (#046B) for credit.
Make sure to add Work and Energy information to your Table
IMPULSE-MOMENTUM THEORY
https://www.youtube.com/watch?v=fdeH6Ksedwk
Impulse is the change in momentum (Δp).
A. Is the impulse when the brick hits the table the same or different as the brick hitting the foam?
When our video presenter jumps from the table, he begins falling.
B. Does his momentum increase, remain constant, or decrease?
C. Does he want to experience a strong force when he lands? Why/why not?
D. How does he protect himself upon landing?
E. Why are running shoes helpful for our feet?
Impulse Notes:
What does it look like when a force is applied to an object?
http://scienceblogs.com/startswithabang/2012/09/15/weekend-diversion-the-physics-of-happy-gilmore/
https://ssl.wsu.edu/wp-content/uploads/sites/510/2015/01/Bat-Ball-Impact-Bat-Ball-Science-Fig-4.1.jpg
https://www.asme.org/engineering-topics/articles/applied-mechanics/engineering-our-favorite-pastime
ADD THE NEXT 4 LINES TO YOUR Notes
Formula: FΔt
Def: product of the average force and the time interval of the collision.
Units: Newton-seconds
Symbol: none
Video: https://www.youtube.com/watch?v=ph48Xwj_eS8
Try the problem from the video
Notes:
F=ma
F=mΔv/t
F-t=mΔv (Impulse-Momentum Theorem)
3. Two Types of Collisions (add to your notes)
Elastic collision. In an elastic collision, the total kinetic energy (energy from movement) in the system is the same before and after the collision. If losses to heat and deformation are much smaller than the other energies involved, such as when two pool balls collide and go their separate ways, you can generally ignore the losses and say that kinetic energy was conserved.
Inelastic collision. In an inelastic collision, the collision changes the total kinetic energy in a closed system. In this case, friction, deformation, or some other process transforms the kinetic energy. If you can observe appreciable energy losses due to nonconservative forces (such as friction), kinetic energy isn’t conserved.
4.