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## Do Now…

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**Do Now…**• Quest will start in a minute… You have 5 minutes to do any last minute preparation!! • Everyone should TAKE A RULER to keep from the teacher’s desk. • If you need to BORROW a calculator, please trade for one now. • **If you did not turn in your Metric Patrol last class, do it now! (10% off each day it is late!**)**When you are done with Quest…**• Place quest in “In Box” on desk • ALL STUDENTS must take a copy of “Supplemental Ch. 1 – Physics” (blue label) • CHOOSE ONE (1) of the vocab worksheets • One is matching • The other is writing down the definition • Use the Supplemental Ch. 1 packet to complete Vocab silently after quest– it is HW if you do not finish in class (5 points) • If you finish the vocab worksheet, come see teacher for a vocab crossword puzzle – just for fun, not graded, but extra practice and a good addition to your notes for future quizzes.**We will be skipping around in your textbook. Covering the**chapters, but not necessarily in sequential order. • You are getting a “Supplemental Ch. 1” packet today –photocopied from newer textbook edition. DO NOT LOSE IT. You may write on it, and it is yours to keep, but you will treat it like your textbook for the next few classes (may leave actual textbook in locker until we are done with Supplemental Ch. 1, but you NEED to bring Supplemental Ch. 1 to class with you.)**Supplemental Ch. 1 - Forces**• A book is on your desk. Suppose you wanted to get that book to move, but you could neither lift it off desk nor lift the desk. What could you do? • When we pushed/pulled the book, did its state of motion change? • YES! It went from REST to MOVING • The state of motion may be either… • One of rest • Or moving in a straight line with an unchanging speed (for example, car is in cruise control, and you are not moving the steering wheel. • 2. A force is needed to change the state of motion of an object.**Supplemental Ch. 1 – Continued..**• We measure force in NEWTONS (N) Just like we use metersnot miles to measure distance, we use Newtonsnot pounds to measure force in the metric system (and weight is a force!) • Look at book on your desk. If you dropped it, would it fall to the ground? • Ok, so we know that the book has weight, which is a force in the downward direction. But is the book actually falling in the downward direction? • Something is supporting it…we call that support force. In which direction does support force act – up or down? • UP!! Otherwise, the book would fall!**Wait a minute…I thought we said that a force is needed to**change the state of motion of an object. This book on my desk has forces acting on it (weight and support forces)…but it is at rest. What’s going on here? • The forces CANCEL, so the NET FORCE is zero. • “NET” means “sum of” and is represented by the Greek letter sigma ∑ • Net force is zero if an object is at rest, or if it is moving in a straight line at the same speed (in either case, the state of motion is not changing…it “keeps on doing what it already is doing”)**Net Force**When the girl holds the rock with as much force upward as gravity pulls downward, the net force on the rock is zero.**2.1Force**Net Force The net force depends on the magnitudes and directions of the applied forces.**2.1Force**Net Force The net force depends on the magnitudes and directions of the applied forces. 1 person pushing with 5N + 1 person pushing with 10 N is equal to 1 person pushing with 15 N**2.1Force**Net Force The net force depends on the magnitudes and directions of the applied forces.**2.1Force**Net Force The net force depends on the magnitudes and directions of the applied forces.**2.1Force**Net Force The net force depends on the magnitudes and directions of the applied forces.**2.1Force**Net Force The net force depends on the magnitudes and directions of the applied forces.**Try #3-9 on your guided notes…(You might want to draw**pictures for #5-8, and 9, just like what we saw on the Powerpoint)**Now, I hold this 500 g mass from a spring scale.**• What happens to the spring? • It stretches! • We call that stretching tension • There are 2 forces acting on this mass – downward force of weight due to gravity, and upward force of tension • Is the mass moving? • So, is it changing its state of motion? • Now, think about what the net force must be… • 0 N, more than 0N, or less than 0 N (heads down) • 0 N! The net force must be zero, because the object is not changing its state of motion!**2.1Force**Tension and Weight The upward tension in the string has the same magnitude as the weight of the bag, so the net force on the bag is zero. The bag of sugar is attracted to Earth with a gravitational force of 2 pounds or 9 Newtons. • The two forces on the bag are equal and opposite. The net force on the bag is zero, so it remains at rest.**2.1Force**Force Vectors A vector is an arrow that represents the magnitude and direction of a quantity. A vector quantity needs both magnitude and direction for a complete description. Force is an example of a vector quantity. A scalar quantity can be described by magnitude only and has no direction. Time, area, and volume are scalar quantities.**2.1Force**Force Vectors This vector represents a force of 60 N to the right. N**2.1Force**Force Vectors Explain**2.1Force**Net Force A force is a push or a pull. A force of some kind is always required to change the state of motion of an object. The combination of all forces acting on an object is called the net force. The net force on an object changes its motion. The scientific unit of force is the Newton, abbreviated N.**2.1Force**Now try #10-13 in guided notes How can you change an object’s state of motion? Exit Slips!