PhysicsLAB CP Workbook
Force and Weight

 
Mass vs. Weight
 
Refer to the following information for the next two questions.

An apple that has a mass of 0.1 kilogram has the same mass wherever it is.
The amount of matter that makes up the apple ____
 
the location of the apple. It has the same resistance to acceleration wherever it is - its inertia everywhere
 
Refer to the following information for the next three questions.

The weight of the apple is a different story. It may weigh exactly 1 N in San Francisco and slightly less in mile-high Denver, Colorado. On the surface of the moon the apple would weigh 1/6 N, and far out in outer space it may have almost no weight at all.
 
The quantity that doesn't change with location is ____
 
and the quantity that may change with location is its ____.
 
That's because ____ is the force due to gravity on a body, and this force varies with distance.
 
Refer to the following information for the next question.

So weight is the force of gravity between two bodies, usually some small object in contact with the earth.
When we refer to the _____ of an object we are usually speaking of the gravitational force that attracts it to the earth.
 
If we stand on a weighing scale and find that we are pulled toward the earth with a force of 500 N, then we weigh ____ N. Strictly speaking, we weigh ____ N relative to the earth. But much does the earth weigh relative to us? If we tip the scale upside down and repeat the weighing process, we can say that we and the earth are still pulled together with a force of ____ N, and therefore, relative to us, the whole 6,000,000,000,000,000,000,000,000-kg earth weighs ____ N! Weight, unlike mass, is a relative quantity.
 
 
 
Gravitation, Planets, and Moons
 
A spaceship is attracted to both a planet and the planet's moon. The planet has four times the mass of its moon. The force of attraction of the spaceship to the planet is shown by the vector.
 
Carefully sketch another vector to show the spaceship's attraction to the moon. Then use the parallelogram method and sketch the resultant force. Describe the direction of the resultant force. 

Determine the location between the planet and its moon (along the dotted line) where gravitational forces cancel.
 
 
Refer to the following information for the next three questions.

Consider a planet of uniform density that has a straight tunnel from the north pole through the center to the south pole. At the surface of the planet, an object weighs 1 ton. Fill in the gravitational force on the object when it is:
halfway to the center. 

then at the center 

Describe the motion you would experience if you fell into the tunnel. 

Refer to the following information for the next three questions.

Consider an object that weighs 1 ton at the surface of a planet, just before the planet gravitationally collapses. (The mass of the planet remains the same during collapse.)
 
 
Fill in the weights of the object on the planet's shrinking surface at the radial values shown.
 
         
at R/2 

at R/10 

When the planet has collapsed to 1/10 of its initial radius, a ladder is erected that puts the object as far from its center as the object was originally. Fill in its weight at this position.
 
 





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