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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/second2 (m/s2)

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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 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**

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**B opposite to the object’s motion C toward the center of the circle **

2.3 Unbalanced Forces and Acceleration In what direction does the net force of an object moving with constant speed and in a circular motion occur? A downward B opposite to the object’s motion C toward the center of the circle D in the direction of the object’s velocity

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**Acceleration depends on both the force applied and ____. **

2.3 Unbalanced Forces and Acceleration Acceleration depends on both the force applied and ____. A distance from the object B speed of the object C mass of the object D normal force of the object

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**A The motion does not change. B The object speeds up. **

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

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**What would cause an object to have a larger acceleration?**

A increasing the net force applied B decreasing the net force applied C increasing the mass and keeping the net force constant D none of the above

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**What causes a change in motion on an object?**

A zero net force B unbalanced force C weight D balanced force

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**For every action force, there is a reaction force that is ____.**

A in the same direction B equal to the two objects C equal and in the opposite direction D unequal 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**

You throw a 2 kg ball with a force of 50 N. What is the ball’s acceleration? A 25 m/s2 B 48 m/s2 C 52 m/s2 D 100 m/s2

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SCI 2.f A tennis ball hit by a racket has an acceleration of 1000 m/s2. If the net force on the tennis ball is 100 N, what is the tennis ball’s mass? A 0.01 kg B 0.1 kg C 1 kg D 10 kg

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