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**FORCES AND NEWTON’S LAWS**

CHAPTER 3

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I. FORCES – 3.1 What is force? 1. Please Define Force: A push or pull exerted on an object.

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**2. Changing motion Net force**

a. Please Define Net Force: Sum of all the forces that are acting on an object.

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4. Unbalanced forces a. Please Define Unbalanced Force: An unbalance force is one that is not opposed by an equal and opposite force operating directly against the force and causes the object to change its motion.

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5. Balanced forces a. Please Define Balanced forces: Forces are balanced when the forces pushing (or pulling) an object in one direction are the same size as the forces acting in the opposite direction.

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B. Friction Please Define Friction: Force that opposes the sliding motion between two touching surfaces.

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2. What causes friction?

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3. Static Friction a. Please Define Static Friction: Frictional force that prevents two surfaces from sliding past each other.

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4. Sliding Friction a. Please Define Sliding Friction: Frictional force that opposes the motion of two surfaces past each other.

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5. Rolling Friction a. Please Define Rolling Friction: Rolling friction is a resistive force that opposes the rolling motion of an object.

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**C. Gravity The law of universal gravitation**

a. Write the Equation for Universal Gravitation: F = G m1m2 d2

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**b. Gravity and you The range of gravity The gravitational field**

(1.) Please Define Field: A region of space in which every point has a physical quantity, such as a force.

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2. Weight Please Define Weight: Gravitational force exerted on an object. Write the Equation for Weight: Fg = mg Weight (N) = mass (kg) x gravitational strength (N/kg)

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c. Weight and mass (1.) Please Define Weight: Gravitational force exerted on an object. (2.) Please Define Mass: Amount of matter in an object.

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**d. Weight on Earth (1.) Write the units of “g” in two different ways.**

(a.) 9.80 m/s2 (b.) N/kg Weight away from Earth 3. Finding other planets

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**II. NEWTON’S LAWS OF MOTION -3.2**

A. Isaac Newton and the Laws of Motion

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**B. Newton’s First Law of Motion**

Please Define Newton’s First Law of Motion: That an object moving at a constant velocity keeps moving at that velocity unless an unbalanced force acts on it.

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2. Inertia a. Please Define Inertia: Tendency of an object to resist any change in its motion.

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3. Inertia and mass

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**C. Newton’s Second Law of Motion**

Force and acceleration Mass and acceleration Relating force, mass, and acceleration a. Please Define Newton’s second law of motion: That the acceleration of an object is in the same direction as the net force on the object, and that the acceleration equals the net force exerted on it divided by its mass.

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**c. Calculating net force**

(1.) Please write net force as an Equation: Fnet = mass x acceleration

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**D. Newton’s Third Law of Motion**

Please Define Newton’s Third Law of Motion: That when one object exerts a force on a second object, the second object exerts a force on the first object that is equal in strength and in the opposite direction. Or for every action there is an equal and opposite reaction.

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**Forces on different objects do not cancel**

Forces are interactions

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**III. USING NEWTON’S LAWS -3.3**

What happens in a crash? a. Safety belts b. Air bags

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b. Air bags

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**B. Newton’s Second Law and Gravitational Acceleration**

Air resistance 1. Please Define Air Resistance: Force that opposes the motion of objects that move through the air.

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2. Size and shape

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**3. Speed and terminal velocity**

Please Define Terminal Velocity: The maximum speed an object will reach when falling through a substance, such as air.

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**b. Free fall Please Define Free Fall:**

Describes the fall of an object on which only the force of gravity is acting.

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2. Weightlessness

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**C. Centripetal Forces Please Define Centripetal Force:**

A force that is directed toward the center of a curved or circular path.

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**D. Force and Momentum Conservation of momentum**

a. Please Define the Law of Conservation of Momentum: That if no external forces act on a group of objects, their total momentum does not change.

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**b. Collisions with multiple objects**

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2. Rocket propulsion

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IV. CHAPTER 3 REVIEW Please do Check Concepts 34-42, found on page 98 in your Text. Please do Standardized Test Practice 1-8, found on page 100 in your Text. I will give you a Pre-Test on Chapter 3 problems for your Chapter 3 Test.

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