Oct. 6 – Unit 2: Introduction and FBD

Congratulations on completing the unit test!  I am busy marking them now and will get you the marks as soon as possible.

In the meantime, we are starting unit 2...

Unit 2: Forces

Here's what movies like Star Wars thinks a "force" is,

What are forces in real life?  Watch this,

Here are the notes I gave in class:

 What is a force?

 - A push or a pull on an object.

 - Cause objects to “move” (acceleration).

Four Fundamental Forces

1. Gravity

        - weakest

        - can only attract (pull)

        - acts on anything with mass

2. Electromagnetism (EM)

        - electricity and magnetism

        - stronger than gravity

        - can attract or repel (push or pull)

        - holds atoms and molecules together

        - most forces you feel on a everyday basis are electromagnetic!

3. Weak Force

        - stronger than EM

        - only affects radioactive nuclei

4. Strong Force

        - strongest of forces

        - holds together protons to create nuclei inside atoms.

Forces are vectors!

        - have magnitude and direction

        - we can represent them with arrows

        - we organize forces with Free Body Diagrams (FBD)

        - draw all the forces acting on an object

Examples: 

An object falling due to gravity.

An object falling due to gravity with air friction included.

Forces add like any vectors would.

The total force on an object is called NET Force (the sum of all force vectors), ∑F.

In the above example: ∑F = F(gravity) + F(air)

NEWTON’S FIRST LAW

(Law of Inertia)

"An object in motion (or at rest) tends to stay in motion (or at rest) unless acted upon by an external force"

More precisely, we can say:

When the net force on an object is zero, the object will move at constant (or zero) velocity.

If ∑F = 0, then a = 0.

or

When an object is moving at constant (or zero) velocity, the net force is zero.

If a = 0, then ∑F = 0.

Example:

An object sitting on the ground.

Using Newton's First Law, the object is not accelerating, therefore, the net force must be zero.  We see that there must be a force opposing gravity, otherwise the object will fall right through the Earth!

This force is 90° from the ground, therefore it’s called the Normal Force.  (Normal = 90°)

The Normal Force comes from contact with a surface (contact force).

Other common forces…

 - Tension: pulling force from a string or rope.

 - Friction: contact force that opposes the direction of motion.

Handouts

• Unit Outline
• Free Body Diagrams

Sept. 30 – Formative Quiz

Here's the formative quiz we did today:

• Formative Quiz

The following is to help you prepare for the test this week...

Test Topics

1. Significant Digits, Units, Scientific Notation (throughout the test).
2. Vectors (adding vectors, vector diagrams, vector components).
3. Definitions (distance, displacement, speed, velocity, acceleration, etc.)
4. Graphing (DT, VT, AT)
5. Kinematic Equations
6. Projectile Motion

Knowledge/Understanding: Multiple choice, some full solutions required.

Application: Problem solving, full solutions required.

Communication: Explanations and diagrams.

Thinking: Challenge Question.

Reminders

• Lab Due Wednesday for P1, Thursday for P5
• Test Thursday
• Thinking Question Friday

Now's the time to buckle down and prepare for the test.  Good luck!

Sept. 26 – Projectile Motion Problems

Announcements

Here's the plan for next week:

• Monday: Work Period
• Tuesday: Formative Quiz
• Wednesday: Review day, Lab Due (period 2)
• Thursday: Test day, Lab Due (Period 5)
• Friday: Thinking Question

Today I worked out some full solutions to projectile motion problems.  Look at this one involving Milos Raonic serving a ball from the top of the CN tower:

The second question involved this golfer:

The video tells us that the ball went 279 yards (we'll make it meters!).  We timed it to find that ∆t = 6.6 s.  We were then able to calculate the initial speed and angle of the hit.  See the full solution above.

In period 5, I also showed the full solution to number 3 of this problem set:

• Advanced Kinematics Problems 1

Homework

• Work on your lab write up.
• Work on day 11 homework from the Unit Outline.

Sept. 25 – Lab Day

Announcements!

Here is a new schedule for the rest of the unit:

• Formative Quiz Tuesday Sept. 30
• Lab due Wednesday Oct. 1 (for Period 2), Thursday Oct. 2 (for Period 5)
• Test on Thursday/Friday Oct. 2, 3

Today the Period 5 class collected data for their lab.  Period 2 class had a lesson on projectile motion.  Please see the notes from yesterday's post.

Homework for Period 2 Class

• Do homework from day 10 in the unit outline.

Homework for Period 5 Class

• Work on your lab writeup.

Sept. 24 – Projectile Motion

Today the Period 2 Class collected data for their lab.

Period 5 had a normal lesson.  Here are the notes from Period 5.
I took up problem 2 from yesterday's handout:

At this point you need the quadratic formula!  Don't remember it?  Listen to this song...

Next we discussed projectile motions.  Here are the notes:

Here are some examples of projectile motions:

I also showed you evidence that X and Y components of velocity behave independently.  Here's how the Mythbusters confirmed that a bullet dropped and fired all fall at the same rate:

Tomorrow, we switch and Period 5 class will collect data while Period 2 class will have the lesson.

Homework for Period 5 Class

• Do homework from day 10 in the unit outline.

Homework for Period 2 Class

• Work on your lab writeup.

Sept. 23 – Advanced Kinematic Equations and Lab Introduced

Welcome back from your long weekend!  I hope you used the opportunity to catch up on all your homework.

I started today by reviewing one of the homework problems:

Then I provided you with some more advanced kinematic problems as well as the lab for tomorrow.  Please have a look at the lab handout and come prepared to collect data tomorrow.

Handouts

• Advanced Kinematics Problems 1
• Advanced Kinematics Problems 2
• Gravity Lab 
• Gravity Lab Marking Scheme

Homework

• Complete any previous homework.
• Work on Advanced Kinematics Problems.
• Read the Lab handout.

Sept. 19 – Kinematic Equations

On Friday I showed you where the 5 kinematic equations come from.

Here is your long awaited formula sheet!

• Formula Sheet

Here are the notes:

This chart is on page 54 in your textbook.  It shows the relations between these 5 equations and the 5 variables.

Example: A light bulb drops from a 3 m ceiling and falls to the floor.  How long does this take?  (Acceleration due to gravity is 9.81 m/s²).

Given: ∆d = 3m [down]        vi = 0 m/s [down]      a = 9.81m/s² [down]

Required: ∆t

Analysis: The third equation contains all these variables.

∆d = vi ∆t + 1/2 a (∆t)²

Solve: ∆t = 0.78 s

Statement: The light bulb takes 0.78 s to fall to the ground.

We then tested it by dropping stuff from the ceiling and got surprisingly accurate results!

Homework

You can now do the homework from day 7 and 8 of the Unit Outline.