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Chapter 6: Motion & Force

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What you should know: Changes in motion and position can be measured. The types of forces that act upon an object can be predicted and measured. Gravity is a universal force that every mass exerts on every other mass. Many forces act at a distance. Common contact forces include friction and buoyancy. An object at rest will stay at rest unless acted upon by an outside force. An object in motion will remain in motion unless acted upon by an outside force.

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Need to Know Formulas: Average Speed = total distance Time Acceleration = Final speed – Initial speed Time Distance = 1/2at² Force = ma Velocity = Change in distance Change in Time Momentum = mass X velocity

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Why do things fall? Gravity- is the attraction between all matter. Isaac Newton was the first to explain how gravity works. Newton’s law of universal gravitation states that all matter in the universe pulls on all other matter. In other words, gravitational attraction exist between you and your desk. The only reason you don’t notice the pull is because gravity is weak between small / distance objects.

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Gravity on earth is 9.8 m/s² Force- is a push or pull Acceleration is a sign that a force is acting Types of forces: –Weight: the downward force of gravity on you. –Normal force- upward force of the ground –Balance forces- when the forces acting on the object cancel each other. Gravity is a Force

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Force = mass X acceleration F=ma SI Unit for Force = Newton's (N) Example: If a force can accelerate 2-Kg mass at 4 m/s², then the force is found as follows: F= (2kg)(4m/s²) = 8N Why is Force SI unit called Newton’s? –Because they are named in honor of Isaac Newton Tools used to measure force: –spring or rubber band –Spring scale

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Inertia, Momentum, and Mass Inertia is a measure of an object’s ability to stay at rest or to keep going. –The tendency of an object at rest to remain at rest, and of an object in motion to remain in motion. Momentum mass X velocity –Property used to understand an objects motion. –Momentum has a symbol of p. –Therefore, p = mv Mass measure the quantity of matter. –Mass stays the same no matter what force is acting on the object.

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Mass and Weight Mass and weight are NOT the same thing, even though they both measure how much there is of something’ Weight is a force due to earth’s gravitational pull. Hence, your weight will change if you travel to the moon.

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Mass vs. Weight Mass Measures the amount of matter in an object Mass does NOT change Tool used: triple beam balance Mass is calculated by grams (g) or Kilograms (Kg) Weight Is a measurement of the gravitational force acting on an object. Weight does change Tool used: scale Weight is calculated by pounds (lbs) or Newton’s (N) Formula: W = mass X gravity W=mg

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Motion Described as a displacement from an original position to a new position Displacement is the distance an object has traveled from a fixed reference point. –Refer to FCAT book pp. 111 fig Distance can be determined by subtraction of the original position to the new position. ( this distance is the change in position) Average speed = total distance Time

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Displacement Example

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Velocity Change in distance per unit of time A vector is a number (a magnitude) together with a direction (compare with scalar). A vector can be represented by an arrow whose length represents the magnitude and the direction represents the direction. Magnitude- the property of relative size or extent (whether large or small);

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Velocity Vector

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Class work: Directions: Answer the following questions, show all work. Write questions and answers. 1.Ms. Margolles mass is 10Kg, what is her weight? 2.Give an example of force? 3.What is a push or pull? 4.What is an objects tendency to remain at rest or stay in motion? 5.Is gravity the same on moon as in the earth being 9.8 m/s²?Explain. 6.What happens if your weight is greater than the normal force of a stool you stand on?

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How do things move? Newton’s Laws of Motion I.Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. states that an object remains at rest or continues in a state of uniform motion if no external force acts upon the object. II.An object that has an unbalanced force acting on it will accelerate in the direction of the force. states that if a net force acts on an object, it will cause an acceleration of that object. III.Forces always occur in equal but opposite pairs. states that for every force there is an equal and opposite force. Therefore, if one object exerts a force on a second object, the second exerts an equal and oppositely directed force on the first one.

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Newton’s First law “ An object at rest will remain at rest or an object moving straight at a constant speed will continue this motion until an unbalanced force acts on it.” –Example: a car crash: your body is at a constant speed until it hits the dash board or window. –Known as the law of inertia.

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Friction Friction- is a force that resist motion between two objects in contact. It always acts opposite in the direction of motion. When an object slows down that means it has negative acceleration. Acceleration means an unbalance force is acting on the object. friction Speed

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Pop Quiz 1.Define friction 2.Define inertia 3.State Newton’s first law of motion 4.Newton’s first law is also known as the law of __________. 5.Give 3 examples of Newton’s first law. Explain every example. 6.Name 3 things that you have learned from this chapter and explain them.

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Class work: Assessment Questions Sect pp. 341 # 1-4 Groups of two You have 20 minutes Answers will be discussed *WRITE QUESTIONS & ANSWERS*

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Newton’s Second Law “ An object that has an unbalanced force acting on it will accelerate in the direction of the force” –Example: Standing at the top of a hill with skates on –Force= mass X acceleration –Acceleration= force mass –The more mass an object has the greater the acceleration.

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Newton’s Third Law “Forces always occur in equal but opposite pairs.” –Example: when you push on a door to open it, the door pushes back on you. –When you jump off a boat, the boat moves back and forth. (you are pushing the boat back with your feet with the same force with which it pushes you forward).

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Class work: Newton’s Laws of Motion Make a pamphlet / Booklet stating all of Newton’s laws of motion. Must include: –Newton’s laws –real life examples (things that you do) –And drawings explaining each example NO one’s booklet should be the same because each and everyone of you do different things for fun / as a hobby.

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