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Newton’s Fourth Law. Universal Gravitation. What is Gravity?. An ATTRACTIVE force between two objects with mass Strength of attraction depends on: Mass of each object (in kilograms ) Distance between the objects (in meters ) Gravitational Constant ( G = 6.67 x 10 -11 N ∙m 2 /kg 2 ).
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Newton’s Fourth Law Universal Gravitation
What is Gravity? • An ATTRACTIVE force between two objects with mass • Strength of attraction depends on: • Mass of each object (in kilograms) • Distance between the objects (in meters) • Gravitational Constant • (G = 6.67 x 10-11 N∙m2/kg2)
Gravitational Proportions The force of gravity is DIRECTLYproportional to the masses of the objects attracted to one another The force of gravity is INVERSELY proportional to the SQUARE of the distancebetween the objects attracted to one another
RATIO METHOD • Ignore any constants • Using the equation as a model, plug in simple numbers (like 1) for all the variables that can change. • Solve for the equation and see what you get • Then change the variables according to what the PROBLEM SAYS and see how your answer changes from your original answer
RATIO METHOD • How does the force of gravity change when both masses double? The force QUADRUPLES!
RATIO METHOD • How does the force of gravity change when the distance doubles? The force decreases to 1/4th
MASS EXAMPLES • How does the force of gravity change when… • One mass is doubled? • Both masses are tripled? • One mass is halved while the other mass is doubled?
DISTANCE EXAMPLES • How does the force of gravity change when… • The distance is tripled? • The distance is halved? • The distance is quartered?
3000 m 6 x 105 kg 4 x 105 kg Calculate the force of gravity between the two asteroids Fg = 1.78 x 10-6 N
Gravitational Fields • Objects with MASS produce gravitational fields • Field lines point inward from ALLDIRECTIONS
SUMMARY • Describe the Force of Gravity • Universal Gravitation Equation? • G = ? • How does gravity change when the masses… • Increase? • Decrease? • How does the force of gravity change when the distance… • Increase? • Decrease?