Monday, November 18, 2013

H Physics Standards: 1c Newton’s 2nd Law of Motion

Objective SWBAT draw free body diagrams

Agenda:1. Warm Up2. P.2 Review Graphing

Worksheet3. P.2 Work on Problem Solving4. P.4 Free Body Diagram

Inquiry

HomeworkStudy Worksheets for Test P.2P.4 Homework #FH6P.2 Test Tomorrow: Study the 2 Bootcamp Worksheets

Warm UpA ball travels 50 meters to the west in 20 seconds.

Find the speed of the ball. Find the velocity of the

ball.

Tuesday, November 19, 2013

H Physics Standards: 1c Newton’s 2nd Law of MotionObjective: SWBAT create free body diagrams.

Homework#FH6

Warm Up Draw a free body diagram

of a skydiver in free-fall while s/he is still speeding

up.

Agenda1. Warm Up2. P.2 Take Test3. P.4 Free Body

Diagram Mini-Lecture

4. Force Stations: Elaborate Section

Wednesday, November 20, 2013

H Physics

Warm Upp.2 Draw a diagram for the following scenario: A cart rolls across a table

with an applied Force of 10N, a frictional force of 5N, no air resistance, and a mass of 2kg. It’s acceleration is

unknown.p.4 Draw a free body diagram of the

above scenario.

Homework#FH6P.4 Finish Force Stations Lab

Standards: 1c Newton’s 2nd Law of Motion

Learning Objective: SWBAT create free body diagrams.

Agenda: 1. Warm Up2. P.2 Finish Exam3. P.2 Begin Force Stations Lab4. P.4 Finish Force Stations Lab5. P.4 Practice Free Body Diagrams

Thursday, November 21, 2013

H Physics

Homework#FH7 P.4Quiz Friday – Free Body Diagrams P.2#FH6 P.2

Warm UpDraw a Free Body Diagram for a car skidding to a stop.

Standards: : 1c Newton’s 2nd Law of Motion

Learning Objective: SWBAT solve problems using Free Body Diagrams

Agenda1. Warm Up2. P.2 Force Stations3. P.4 Collect Force Stations Lab4. P.4Free Body Diagram Problem

Solving Guided Practice5. P.4Practice #FH7

Friday , November 22, 2013

H Physics

HomeworkP.2 #FH7P.4 #FH8

Warm UpCreate a free body diagram of a car driving down a hill

where friction & air resistance will affect the

car’s motion.

Standards:  1c Newton’s 2nd Law

Objective; SWBAT will score 80% on the quiz.

Agenda: 1. Warm Up2. P.4 Quiz 63. P#4 Introduce #FH8 Free Body

Diagram Problem Solving4. P.2 Force Stations Lab5. P.2 Guided Practice Free Body

Diagrams

Symbols, units and equations Study Guide

Equations:

Constant Velocity

Constant Acceleration

1.

2.

The Two equations of Motion The Two equations of Motion for Falling Objects ag=-9.8m/s2

Forces

Symbol Units

t s

v m/s

a m/s2

F kgm/s2 or N

Δx m

Types of Forces• From your book p. 94 Table 4-2

Force Symbol Definition Direction

Friction Ff Resistive Force. Comes from rubbing against or sliding across surfaces.

Parallel to the surface and opposite the direction of sliding

Normal FN The force exerted on an object by the ground, a table, a platform, or any surface.

Perpendicular to and away from the surface.

Spring Fsp Restoring Force. The push or pull a spring exerts on an object.

Opposite the displacements of the object at the end of the spring.

Tension FT The pull exerted by a string, rope, or cable when attached to something.

Away from the object and parallel to the string, rope, or cable at the pont of attachment.

Thrust, Applied Force Fthrust,Fap A general term for the forces that move objects such as rockets, planes, cars and people.

In the same direction as the acceleration of the object.

Weight Fg Attractive Force of two objects due to gravity. Usually Earth and and object

Straight down towards the center of the earth.

Air Resistance/Drag FAR Resistive Force, comes from air/wind hitting moving objects

Opposite of Motion

Modeling the Graphing Process

Step One – label each axis with the symbol and the units being represented by the graph.

1st column x-axis, 2nd column y axisStep Two – Create your x and y axis scales. To create a scale(your numbering system on the graph) look at your smallest and largest data points. Then pick a number sequence (ex. 1,2,3,4 or 2,4,6,8) that will allow all of the points to fit on your graph. Step Three – Plot the Points. Step Four – Make a best fine line. It has to be straight and you need to make it go through the center or through the average of your points. See board for more explanation.Step Five – Find the slope of the graph. Step Six (Honors Only) – Find the equation of the graph by substituting your data into the formula y=mx+b

Force Stations• Objective: Gain an introduction to free-body diagrams (FBDs), and create accurate FBDs

of physical systems at stations around room.• Engage• Watch discovery channel video clip on the physics of skydiving (~3 min.):

http:/www.youtube.com/watch?v=ur40O6nQHsw . • Explore• Students rotate around force stations in the room and explore each system ~16 min

o Identify the Labeled Stationo Explore each station: 2 minutes, identify all the forces acting on the object, and draw all the forces on the object.

1. Object at rest on table2. Cart rolling across table3. Object hanging by string4. Object hanging by two strings at an angle to each other5. Ball rolling down ramp6. Object stationary on ramp7. Ball falling through air8. Coffee filters falling through air

• Explain• Mini-lecture on FBDs (Free Body Diagrams) ~5 min• Students revise any force station FBD that is incorrect.• Students finish guided practice problem. • Elaborate• Using magazines provided in class, cut out a picture that shows an interesting physical

scenario. Then students create FBD for one or multiple objects in the cutout picture.• Evaluate• “Free-Body Exercises: Linear Motion” #F6

For the full 10 pts of credit requires full completion of explore, explain, elaborate, and evaluate sections. Evaluate is Homework worth 10 points.

HW: #FH6

After you create each free body diagram, use your free body diagram to make an Fnet=ma equation in the x direction and in the y direction like we did during the Explain portion of the lesson.

Ex

``` `

FN

Fg

FAPFFFAR

Fnetx=Fap-Ff-FAR=macar-x-direction

Fnety=FN-Fg=macar y-direction

Free Body DiagramsWhat are they? – These are diagrams similar to the one’s we are used to drawing, but with one major exception. You only put Forces on them.

Why do we make them?1. They help us solve

problems involving multiple forces.

2. Looking at the diagram to the right. Fnetx=Fap-Ff-FAR

Fnety=FN-Fg

``` `

FN

Fg

FAPFFFAR

When do we make them?Remember Fnet=ma? You create a free body diagram to help you find the Fnet portion of this equation.

Fnetx=Fap-Ff-FAR=macar-x-direction

Fnety=FN-Fg=macar y-direction

Question: If the car has a 2000 kg mass, its applied force is 10,000 N, friction is 1500 N, and Air Resistance is 1000 N, find the car’s acceleration and the *Normal Force acting on the car?

Free Body Diagrams #FH7For each problem:a. Draw a Free Body Diagram of the problem. b. Make an equation for Net Force in the x (horizontal)

and y (vertical) directions. c. Then plug in the numbers and Calculate the net force

in the x direction and then the y direction.d. Find ax and ay

1. A man pushes a 5kg box with 15 N force to the right while it encounters a 10 N friction force.

2. An 1kg egg is free-falling from a nest in a tree. Neglect air resistance.

3. A 2kg flying squirrel is gliding (no flapping wings) from a tree to the ground constant velocity.

4. A rightward force of 10 N is applied to a 1kg book in order to move it across a desk. Consider a frictional force of 4 N.

5. A 50kg gymnast is suspended motionless from the ceiling by a bar and two vertical ropes, each with a 25 N force.

Problem Solving using FBD’s #F8

1. If a car’s engine accelerates the car using 50,000 N of Force. Friction is resisting the motion with 12,000 N. Find the acceleration of the 2000kg car?

2. If a 60kg skydiver is freefalling towards the ground, and the air resistance half way to the ground is 500 N. What is the net force on the skydiver?

3. From Problem 2, what is the acceleration of the skydiver? 4. If a 70 kg skydiver is freefalling at terminal velocity, what is

the air resistance that the free faller is experiencing. 5. If a 1200 kg car’s engine applies 50,000 N to accelerate the

car and it achieves a 2.5m/s2 acceleration, how much friction is acting on the car? (Assume air resistance is negligible.)

6. If a 20 kg slab of wood is being accelerated on ice at 1.25 m/s2 and friction is small at 5 N. What is the applied force on the slab of wood?