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Published byDeirdre Heath Modified over 5 years ago

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SECTION 3 Motions and Forces

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A. Second law of Motion An object acted on by an unbalanced force will accelerate in the direction of the force.

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1. Acceleration equals force divided by mass, or a=force/mass

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2. Force is equal to the combination of all forces, or the total force that acts on an object.

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B. Second law can also be used to find force if mass and acceleration are known.

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1. Near Earth’s surface, the force of gravity causes all objects to fall with the same acceleration – 9.8m/s2

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A. For any object that is falling, the force of gravity equals mass times acceleration due to gravity, or F=m X (9.8 m/s2)

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2. Weight and Mass are not the same thing.

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A. Weight changes when the acceleration due to gravity changes.

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B. Mass remains the same no matter what weight is.

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C. Friction A force that resists motion and is always present between two moving surfaces.

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1. Static Friction- Keeps a stationary object from moving on a surface when a force is applied to the object.

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2. Sliding Friction Occurs when two surfaces slide past each other; slows down the moving object.

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3. Rolling Friction Friction between a surface and a wheel when the wheel rolls over the surface.

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4. Air resistance- Typical action of air molecules on a forward- moving object, slowing its motion.

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Section 4: Newton’s Third Law A. Third law of Motion- Forces always act in equal but opposite pairs.

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1. When a force is exerted on an object, the object exerts the same amount of force.

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2. Third law of motion applies whether forces are contact or Long- range.

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B. Things move because action and reaction forces work on different objects.

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1. Friction is a factor in the third law.

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2. Using the second law equation, the object with the larger mass has the smaller acceleration if the same force is applied.

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3. All objects in the universe exert a force on all others; however, differences in mass may make these forces unnoticeable.

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C. The three laws of motion described how any object moves when forces act on it.

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