Lesson 3: Chapter 3: Gravitational Interaction

Law of Gravity

- F = GMm/d^2 - every object attracts every other objet by a long-range gravitational interaction

Why do objects hit the ground at the same time in a vacuum?

- F=ma - F=GmM/d² - substitute ma for F - a=-G(M/r²) - acceleration only depends on the gravitational constant, the mass of Earth, and the distance between the objects

G

- gravitational constant - number relating the strength of the gravitational force to the masses being attracted and their distance apart - 6.67 x 10⁻¹¹

Weight

- the gravitational force on an object due to the planet - measure of the force of gravity pulling on an object

All objects weigh less near the surface of the moon than the same objects weigh near the surface of the earth. This is because A. the moon has less mass than the earth. B. the moon has a smaller radius than the earth. C. there is less air on the moon's surface. D. the universal gravitational constant is smaller near the moon. E. the buoyant force on the moon is greater than on earth.

the moon has less mass than the earth

Suppose I drop a rock the same time a ball which was dropped from above passes the rock. (Someone a few meters above you drops a ball. When that ball is even with your hand, you let go of the rock you're holding.) What would you say about the accelerations of the two objects? A. The ball has a greater acceleration than the rock. B. The rock has a greater acceleration than the ball. C. The rock and ball have the same acceleration.

the rock and ball have the same acceleration

The next three questions, Questions 2 - 4, relate to a cannon ball and a marble that are dropped from the same height at the same time. Both are originally at rest. Ignore air friction. How do the speed and acceleration of the cannonball compare with those of the marble at any given time after they are dropped? A. The speed and acceleration of the cannonball are both greater than those of the marble. B. The speed and acceleration of the cannonball are both smaller than those of the marble. C. The speed and acceleration of the cannonball are both the same as those of the marble. D. The speed of the cannonball is the same, but the acceleration is larger. E. The acceleration of the cannonball is the same, but the speed is larger.

the speed and acceleration of the cannonball are both the same as those of the marble

Two objects are attracted to each other by gravitational forces. Suppose I double the mass of one of the objects. This changes the gravitational forces between them. I can make this force the same as it was at first, however, by A. increasing the distance between the two objects. B. decreasing the distance between the two objects. C. increasing the mass of the other object. D. doing nothing--the force is not changed unless I change the mass of both objects, since the gravitational force depends on both these masses. E. decreasing the distance between the objects and increasing the mass of the other object.

increasing the distance between the two objects

As a body moves higher and higher above the surface of the earth, A. its weight increases. B. its mass increases. C. its weight decreases. D. its mass decreases. E. both its weight and its mass decrease.

its weight decreases

g

symbol representing the acceleration caused by gravity - it's equal to 22 mi/hr per second or 32 ft/second per second or 9.8 m/second per second

What is the acceleration due to gravity of the apple when on the moon compared to the acceleration due to gravity of the same apple when it is on the earth? A. The acceleration of the apple on the moon is larger than the acceleration of the apple on the earth. B. The acceleration of the apple is the same whether on the moon or on the earth. C. The acceleration of the apple on the moon is smaller than the acceleration of the apple on the earth.

the acceleration of the apple on the moon is smaller than the acceleration of the apple on the earth

Which will hit the ground first? A. The ball will hit the ground first B. The rock will hit the ground first C. The rock and ball hit at the same time

the ball will hit the ground first

Which is easier to accelerate? A. The cannonball requires more force to accelerate it as much as the marble. B. The cannonball requires less force to accelerate it as much as the marble. C. The cannon ball and the marble will accelerate the same amount in response to the same force.

the cannonball requires more force to accelerate it as much as the marble

If d2 is twice as large as d1, how is the force different? A. In both situations, the force remains the same. B. The force increases when the distance is d2. C. The force decreases when the distance is 𝑑2

the force decreases when the distance is d2

If d2 is equal to d1, but m2 is twice as large as m1, how is the force different? A. The force remains the same B. The force increases C. The force decreases

the force increases

What is the relative strength of the gravitational force on the apple when it is on the moon compared to the gravitational force on that same apple when it is on the earth? A. The gravitational force on the apple due to the moon is larger than the gravitational force on the apple due to the earth. B. The gravitational force on the apple is the same strength whether on the moon or on the earth. C. The gravitational force on the apple due to the moon is smaller than the gravitational force on the apple due to the earth.

the gravitational force on the apple due to the moon is smaller than the gravitational force on the apple due to the earth

The next three questions, Questions 2 - 4, relate to a cannon ball and a marble that are dropped from the same height at the same time. Both are originally at rest. Ignore air friction. How does the gravitational force on the cannonball compare with that on the marble? A. The gravitational force on the cannonball is larger. B. The gravitational force on the cannonball is smaller. C. The gravitational force on the cannon ball is the same as the force on the marble.

the gravitational force on the cannonball is larger

What is the mass of an object, say an apple, on the moon compared to the mass of the same apple on the earth? A. The mass of an object is the same on the moon and on the earth. B. The mass of the object is greater on the moon. C. The mass of the object is greater on the earth.

the mass of an object is the same on the moon and on the earth