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2-3 Notes: Unbalanced Forces & Acceleration Chapter 2, Lesson 3

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Unbalanced Forces & Velocity Whenever an object’s speed or direction changes, an unbalanced force must be acting on the object.

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Unbalanced Forces & Velocity When a resting object is acted on by an unbalanced force, the object will accelerate in the direction of the unbalanced force.

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Unbalanced Forces & Velocity An object’s speed will increase when a net force acts in the same direction as the object’s motion.

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Unbalanced Forces & Velocity An object’s speed will decrease when a net force acts in the opposite direction of the object’s motion.

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Unbalanced Forces & Velocity Unbalanced forces can cause an object to speed up, slow down, or change direction. The rail exerts an unbalanced force on the ball, changing the ball’s motion.

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Unbalanced Forces & Velocity A ball tied to a string and swung in a circle is an example of circular motion.

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Unbalanced Forces & Velocity During circular motion, the centripetal force acts perpendicular to the velocity, toward the center of the circle.

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Newton’s Second Law of Motion When an object changes speed or direction, its velocity changes, and the object is accelerating.

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Newton’s Second Law of Motion Newton’s Second Law of Motion states that the acceleration of an object equals the net force divided by the object’s mass. a = F ÷ m F = ma

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Newton’s Second Law of Motion In the equation representing Newton’s Second Law of Motion: –Force is measured in Newtons (N) –Mass is measured in kilograms (kg) –Acceleration is measured in meters/second 2 (m/s 2 )

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Newton’s Second Law of Motion F = ma ↑ force = ↑ acceleration ↑ mass = ↓ acceleration

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Newton’s Second Law of Motion When the net force is zero, the acceleration is zero. When the acceleration of an object is zero, the velocity is constant.

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Newton’s Second Law of Motion When the fluid friction force (air resistance) is equal to the gravity force (weight), an object reaches its terminal velocity. It no longer accelerates, and will remain at whatever velocity it was already traveling.

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Newton’s Second Law of Motion Terminal velocity for a human is 118-125 mph.

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Newton’s Second Law of Motion When the net force is NOT zero, the velocity of the object changes.

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Newton’s Third Law of Motion Newton’s Third Law of Motion states that when one object exerts a force on a second object, the second object exerts an equal force in the opposite direction on the first object.

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Newton’s Third Law of Motion The forces two objects exert on each other are called force pairs. The forces in a force pair are equal in size, and opposite in direction.

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Newton’s Third Law of Motion One of the forces in a force pair is called the action force and the other force is called the reaction force.

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BrainPOP! Newton’s 3 Laws http://glencoe.mcgraw- hill.com/sites/0078741858/student_view0/br ainpop_movies.html

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In what direction does the net force of an object moving with constant speed and in a circular motion occur? Adownward Bopposite to the object’s motion Ctoward the center of the circle Din the direction of the object’s velocity 2.3 Unbalanced Forces and Acceleration

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Acceleration depends on both the force applied and ____. Adistance from the object Bspeed of the object Cmass of the object Dnormal force of the object 2.3 Unbalanced Forces and Acceleration

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How does the motion of an object traveling in a straight line at 5 m/s change if a balanced force is applied? AThe motion does not change. BThe object speeds up. CThe object slows down. DThe object travels in a horizontal circle. 2.3 Unbalanced Forces and Acceleration

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What would cause an object to have a larger acceleration? Aincreasing the net force applied Bdecreasing the net force applied Cincreasing the mass and keeping the net force constant Dnone of the above

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What causes a change in motion on an object? Azero net force Bunbalanced force Cweight Dbalanced force

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For every action force, there is a reaction force that is ____. Ain the same direction Bequal to the two objects Cequal and in the opposite direction Dunequal and in the direction of the object with less mass

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You throw a 2 kg ball with a force of 50 N. What is the ball’s acceleration? A25 m/s 2 B48 m/s 2 C52 m/s 2 D100 m/s 2

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A tennis ball hit by a racket has an acceleration of 1000 m/s 2. If the net force on the tennis ball is 100 N, what is the tennis ball’s mass? A0.01 kg B0.1 kg C1 kg D10 kg SCI 2.f

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