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SPS8.c Relate falling objects to gravitational force.

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SPS8.d Explain the difference in mass and weight.

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EQ: How do weight and mass differ with respect to gravitational force?

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Weight and Mass

How are weight and mass related?

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12-2-1 Weight and Mass

• weight: a measure of the gravitational force exerted on an object

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12-2-2 Weight and Mass

Weight is equal to mass times free-fall acceleration.

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12-2-3 Weight and Mass

• weight = mass x free-fall acceleration, or w = mg

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12-2-4 Weight and Mass, continued• Weight like force is measured in newtons.

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12-2-5 Weight and Mass, continued

mass = a measure of the amount of matter in an object

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12-2-6 Weight and Mass, continued

weight = the gravitational force an object experiences because of its mass

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Law of Universal Gravitation

Why do objects fall to the ground when dropped?

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12-2-7 Law of Universal Gravitation

All objects in the universe attract each other through the force of gravity.

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12-2-8 Law of Universal Gravitation, continued• Newton’s law of universal

gravitation gives the size of the gravitational force between two objects:

1 22

m mF G

d

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12-2-9 Law of Universal Gravitation, continued

1 22

m mF G

d–m1 and m2 are the masses

of the two objects–d is the distance between

the two objects

–G is a constant

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12-2-10 Law of Universal Gravitation, continued• All masses have gravitational attraction for other masses no matter how small or large the mass is.

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12-2-11 Law of Universal Gravitation, continued

• Gravitational force increases as mass increases and

• decreases as distance increases.

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Law of Universal Gravitation, continued

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12-2-12 Free Fall

In the absence of air resistance, all objects falling near Earth’s surface accelerate at the same rate regardless of their mass.

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12-2-13 Free Fall

• free fall: the motion of a body when only the force of gravity is acting on the body

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12-2-14 Free Fall, continued

• Air resistance can balance weight.

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12-2-15 Free Fall, continued

terminal velocity: the constant velocity of a falling object when the force of air resistance is equal in magnitude and opposite in direction to the force of gravity

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Projectile Motion

Why does a projectile follow a curved path?

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12-2-16 Projectile Motion

Projectile motion has two components—horizontal and vertical, which combine to form a curved path.

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12-2-17 Projectile Motion

• projectile motion: the curved path that an object follows when thrown, launched, or otherwise projected near the surface of Earth

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12-2-18 Projectile Motion, continued

After you have thrown a ball, no horizontal forces are acting on the ball (if air resistance is ignored). So, the horizontal component of velocity of the ball is constant after the ball leaves your hand.

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12-2-19 Projectile Motion, continued

When you throw a ball, gravity pulls it downward, which gives the ball vertical motion. In the absence of air resistance, gravity on Earth pulls objects that are in projectile motion downward with an acceleration of 9.8 m/s2, just as it pulls down all falling objects.

Section 2Forces

Projectile Motion, continued

• Orbiting is projectile motion.