By: Antoine Boyer, Rob Ironside, and Jacqueline Mersereau

· What is the law?

o A body at rest remains at rest or a body in constant motion remains in constant motion along a straight line unless acted on by an external force.

· What is the mathematical interpretation of the law?

o If ∑F = 0, then a = 0.

o If ∑F = 0, then v = a constant.

· In what scenarios or under what conditions is this law valid?

o This law is applicable when there is either “no force” or “zero net force” acting on the body. The body must be moving with a constant velocity and be at rest, it cannot be connected to any form of acceleration. As well, if the body is moving, it must be in a straight line with no changes in direction and with no net force acting on the body.

o Net force is expressed as the combination of all forces acting on an object described as a vector.

· What do you have to consider when applying this law?

o When applying this law we must consider that no force is irrelevant on earth because all bodies in our immediate surroundings are acted on by gravity. Velocity is equal to zero when an object is stationary within its frame of reference. As well, when the net external force on a body is equal to zero then the velocity is constant.

· What is the history of the development of this law?

o Galileo Galilei and Isaac Newton developed this law in the 1600s. Before Newton developed the idea of inertia, the more popular and accepted theory was that “there is a natural tendency of objects to come to rest at a position.” For nearly 2000 years before Newton’s first law people believed that if a moving object, when left alone would eventually come to a stop completely of its own accord. We now know that a moving object left on its own will come to a stop but only because of friction, without friction it would continue to move in a straight line indefinitely.

· How does this law fit into what you have learned already?

o This law can be related to our first physics project, ‘Stop on a Dime.’ In this project we had to design a car, which would go down a one-meter ramp and travel three meters before coming to a complete stop directly over a dime. Inertia states that our vehicle would be both reluctant to start moving in the first place as well as to stop once it had started moving. Since this was clearly no the case, since our car moved and eventually stopped, we know that there are factors that affect inertia. In this situation the two most obvious would be gravity and friction. An object at rest may be forced to move by gravity, even though inertia states that it would otherwise remain still. An object may be forced to stop due to friction even though inertia states that it would, under other conditions, remain moving at a constant velocity in a straight line indefinitely.

· How do you see this law in play in everyday life? For practical purposes?

o This law can be seen in play in everyday life in a number of different situations as well as be used for practical purposes. One very common example of this is the installment of airbags and seatbelts into cars. When a car brakes suddenly or is unexpectedly stopped, such as in an accident, the occupants of that car continue to move. Since they are not directly a part of the car, and have therefore not been stopped, inertia causes them to continue moving which can in many conditions result in people flying from cars resulting in serious injuries or death. This has affected the instatement of airbags and seatbelts in cars, to prevent inertia from completely throwing bodies from vehicles.

Citation:

Kumar Singh, Sunil. “Newton‘s First Law of Motion.” Connexions. 04/July/2007. 29 Sep 2008 <http://cnx.org/content/m14041/latest/&#62;.

Lennard, Jim. “Newton‘s First Law.” Physics in Sports. Universal Gravitation. 29 Sep 2008 <http://archive.ncsa.uiuc.edu/Cyberia/VideoTestbed/Projects/NewPhysics/newtons_1.html&#62;.

Fudge, Shane. “General Information About Newton‘s 3 Laws.” The Physics Behind Air Bags and Crumple Zones. 29 Sep 2008 <http://www.k12.nf.ca/gc/Science/Physics3204/Projects2003/SlotA/ProjectA2/index1.htm>.

Physics Answers Part 1

Physics Answers Part 2

For homework, please review the hardcover Physics text page 180-182; I would like you to read through the problems and bring questions to class. If you understand it, please attempt questions 18-20 on page 182. Please ensure you have page 114 #1-4 from the softcover Physics 20 text completed for tomorrow.

Tuesday Oct. 14:Review of test 1, lesson Newton’s third law as well as a recap of normal force and friction

Wednesday Oct. 15: Review of Newton’s third law problems. There will be an availability from 3:30-4:30PM at the Academy for physics students who require some extra help.

Thursday Oct. 16: Test on Newton’s Laws

Friday Oct. 17: Review of test 2, students will be given a review of topics covered, sections to review as well as problems to attempt for the midterm. We will also review problem solving strategies for the midterm on this date.

• 6-8 hours for mathematics
• 10-12 hours for chemistry
• 10-12 hours for physics

Students may require more or less time in each subject so please use this as a guideline only. If you need more time than the recommendation to understand one topic, please schedule more time. If you have questions about any of the material, please make sure to see me at some point this week (DO NOT save it for the night before the midterms!).

For those who need a review of frictional forces, please refer to your Physics text on page 141; there is a summarized section on the topic. Friction is covered on page 137-141 if you need a more thorough review.

• Position-time graphs, velocity-time graphs
• Force of friction (what is it? what affects it?)
• Displacement and distance calculations
• Velocity and speed calculations
• Acceleration calculations

Please be familiar with both the concepts (definitions, how ideas are applied) as well as be comfortable with manipulating equations.

Your text includes a unit review from page 118-121; questions 34 onward have answers in the back if you need to review the calculations portion of your understanding. Please review the problems you have done in the past as well as these problems for review.

Newton’s Laws Presentation

The formulae we used for motion analysis (acceleration, displacement, velocity) will be provided.

Design Journal (20)
The design journal is meant to illustrate your creative process. The design journal should document the things that you thought of, that you tried, would like to try, etc. Why did you think it was a potential idea? If they didn’t work, why didn’t it work? If you didn’t have the means to carry out the idea, what would you have needed? Please write this section in paragraphs. This section should demonstrate to me thoughtfulness and detailed consideration.

Design Schematic (10)
This should be some kind of drawing of your design. Please label your parts (what did you use?) and provide dimensions when possible.

Design Justification (20)
This section should describe why you made certain choices and why different elements of your vehicle were put in place. Elaborate on why you used certain materials, shapes, etc and tell me their advantage over other possibilities that you considered. Apply any scientific knowledge you have here when you can or mention your hypothesis (ex. “I think this material will make my vehicle go faster because it resembles other materials that have this property”).

Trials, Tests, Observations (10)
Please include any tables or charts showing your testing. This will section will help keep track of any improvements that result from different adjustments.

Product (10)
You will be evaluated on your product itself. Some of the considerations for your product include: originality, stability (does it fall apart quite easily?), efficiency of materials (did you require many expensive parts? Were you efficient in your use of materials), etc.

Performance (20)
20% of the mark will be based on whether your vehicle achieves its objective of stopping on a dime. This section will be evaluated as follows:
Distance Away  (cm)    Mark Out of 20
0                                                 20
5                                                 19
10                                               18
15                                               17
20                                               16
…                                                …

Peer Evaluation (10)
Part of your mark will be assigned by your group members based on your teamwork abilities and contributions. Individuals will be peer evaluated on these criteria:

• Did he/she contribute positively to the team structure? (/5)
• Was she/he able to stay on task and help keep the team on task? (/5)
• Did he/she participate in discussions and contribute ideas? (/5)
• Did she/he work collaboratively? (/5)
• Did he/she take initiative in getting tasks done? (/5)
• Did she/he do an equal share of the work?
  1-    Did no work
  2-    did very little
  3-    did some work
  4-    did their equal share
  5-    did more than their equal share

You will also be asked to provide some anecdotal comments to justify the mark you have assigned. This section will be done individually.

Friction: is the force that inhibits motion between objects in contact with each other

Static Frictional Force: exists when you start to move an object from rest

• When an object is at rest, there are strong attractive forces between the two surfaces. When you push on an object, the static friction “pushes back”. The object will only start moving when the force applied exceeds the frictional force.

Kinetic Frictional Force: exists while the objects are in motion

• When the object is in motion, new attractions between new molecules continually form and break (think “stick and slip”).

Coefficient of Friction: “stickiness value”, gives an idea of the nature of two interacting surfaces

Normal force: the force that is perpendicular to the mass/surface

• The normal force describes the force that is being applied to the surfaces in contact
• Often described by mg

• The strength of the frictional forces is dependent on the nature of the surfaces
• All surfaces, no matter how smooth in appearance, have a force of friction associated (hidden, microscopic imperfections)
• Frictional forces depend on the normal force and the surface type (not on surface area).
• The guidelines for friction do not apply if the surfaces are not flat (ex. On an angle, tire treads)

The formula for friction is F(f)= uF(N) (“force of friction is equal to the coefficient of friction multiplied by the normal force”)

Inertia: the natural tendency of all objects to resist a change in motion. The amount of inertia is directly related to mass.

Example: being jerked forwards when a bus stops abruptly and being thrown backwards when a bus accelerates to start again.

The idea is that an object will remain at rest or in uniform motion unless acted on by an external force. (ex. Friction)

A state of uniform motion is as natural as a state of rest. A ball would hypothetically keep rolling on a surface forever if friction didn’t affect it.

We are now learning about dynamics: why objects move the way they do (examining force)

What is a force?

A force is a push or pull on an object

Forces can cause change in motion

Physicists use term “inertial mass” to describe an object’s resistance to changes in motion.

Gravitational mass describes how two masses will interact and exert a gravitational force on each other.

Inertial and gravitational masses are two different manifestations of the same property.

Types of Forces

Contact Force: when there is direct contact between objects

Non-contact force: act over a distance. Example: magnets

Gravitational force: describes the forces that masses exert over each other. The most common use of the term “gravitational force” is to describe the Earth’s pull on us. Earth is very massive so we notice its force much more than the forces of other objects.

Gravitational forces act in pairs; we exert equal force on the Earth as it does on us.

The mutual attractive force between 2 masses acts along the line joining their centres.

The strength of the attractive forces diminishes as the distance between the centre diminishes.

Weight

Clarification of terms: Mass is a value that does not change. The mass of an individual on the surface of Earth is the same as if the individual was on the surface of the moon.

Weight is not the same as mass.  Weight is defined as the force of gravity acting on a mass. An individual’s weight on the moon is much less than on the surface of the Earth because the moon is smaller and thus has a smaller gravitational force.

Summary:

Force of gravity is influenced by the masses involved as well as the distance between the centres of two masses.

Aristotle once suggested that objects would fall at different rates based on their masses. He suggested that heavier objects would fall faster and lighter objects would fall much more slowly. This idea was rejected by Galileo; Galileo correctly postulated that objects all would accelerate at the same rate. This is true when air resistance is not a factor.

The acceleration due to gravity, g, is “constant”.

In reality, the acceleration due to gravity on Earth is almost constant but does change depending on how far away from the centre of Earth one is. Earth is not perfectly spherical and bulges out at the equator. Therefore, the acceleration at the poles is slightly larger than at the equator because it is closer to the Earth’s centre there. The acceleration is slightly different between mountains and valleys as well.

The acceleration on other planets is different because the force they exert is different. The moon is much smaller than Earth and has an acceleration of 1.64 m/s². Jupiter is much larger than Earth and has an acceleration of 25.9 m/s².

We can express the weight of an object by Fg:

Fg = mg

Fg= mass*acceleration = kg(m/s²) = N

Force is described by the unit Newton (N). It is always written as a capital N.

For homework tonight, please complete questions 1-4 on page 137.

For tomorrow: Please be ready to work on your design and start building your vehicles! Use your classtime wisely to avoid having to take things back and forth from the residence.

We also started learning about representing vectors. This is covered on page 90, chapter 3.2 of your text. We learned how to “add” vectors by drawing them “tip to tail”. The goal of this is to be able to find a resultant vector (ex. the actual displacement from start to finish). For this section, we are only “adding” by drawing the vectors out- we are not doing the mathematical summation yet! Your answers will be scale drawings that keep in mind magnitude and direction of vectors.

For homework, please complete page 94 #8-11. I will ask you to submit your answers so I can see your drawings and answers.

For homework, please complete page 116, #1-7 and question 7 from page 89 if you did not complete it.

Stopping on a Dime: We will also be working on an engineering project over the next couple of days. Please take a look at this lab (page 83) and think about what you might need in terms of materials.

Whenever you have some form of an equation that resembles the top equation, you can solve for your unknown using the second formula. a, b, and c represent some numerical coefficient. You will be left with two possible values of x; verify which x makes sense (example: negative time makes no sense so is an invalid number). In the context of our questions, we can use the formulae about to solve for t.

** You do not need to know how we derived it (at least not yet)! Don’t panic! We are just going to work with applying the equations to problems for now.

Please keep in mind that these equations apply:
1) Only in situations of uniform acceleration
2) Only in one direction at a time (ex. just North-South, East-West, vertically, horizontally)

To review this material, please complete page 80 and 89 from #1-7 for homework. Also review page 83 as this is the project that we will be working on in the next while.
Reminder: Newton’s 2nd Law Lab is due tomorrow (Sept. 10)

Newton’s 2nd Law Lab Handout

Page 51- Average Velocity and changing directions; shows a different way of graphing position and time (having negative values represent a direction)

Page 55- Instantaneous Velocity box

Page 58- Concept Organizer (shows the different between constant, instantaneous and average velocity)

Please complete the Quick Lab on page 53 (“Velocity and Time Intervals”). This will be due in class the next day (you will be handing it in to me).

Notes from today’s powerpoint:

Type of Velocities

Page 41- Conceptual Questions

Page 46- Questions 1, 3, 5, 6

There is a lot of information for you to absorb! I encourage you to work together and help each other better understand the concepts. Attached are the powerpoint notes from today (minus the equations):

Displacement and Velocity

• Assignments need to be shared with the instructor by 8AM on the due date. A late submission will result in a zero (8:01AM is late!).
• Assignments should be shared with dman@classafloat.com.
• It is the responsibility of the student to ensure that their assignment is properly submitted. Students should double-check that they are sharing with the right e-mail address and that the assignment was properly posted. If the assignment does not appear in the instructor’s account by 8AM, it is late (this is not negotiable).  To avoid hassle, try test-sharing an assignment at the beginning of the year to ensure that you have the correct e-mail and do not leave things to the last minute.
• If you have any questions or problems with setting up an account or using Google Docs, please refer to the video or ask Ms. Man (in person or via e-mail).

Term Grade (issued in November and April for 1st and 2nd semester respectively):
Term One Course Work (all assignments and tests between the start of the course and midterms)- 50%
Midterm Exam- 50%

Final Semester Grade (issued in January and June for 1st and 2nd semester respectively):
Term One Grade- 25%
Term Two Course Work (all assignments and tests between midterm and final exams)- 25%
Final Written Exam- 40%
Final Oral Defense- 10%
Total: 100%

Physics Syllabus