Name: _______________________ PRINT PLEASE!! .......ID#___________________

__________________________________________________________________

(1) When talking about how some quantity (e.g. acceleration) depends on another quanity (e.g. force applied) it is useful to use the idea of proportionality. It is just a way of talking about an equation. Saying how one property (e.g. acceleration) relates to another property (e.g. mass).

• Aµ B means A is proportional to B. An increase in B results in A increasing proportionally. Doubling B doubles A, tripling B triples A, etc.;

• Aµ1/B means A is inversely proportional to B. An increase in B results in A decreasing proportionally. Doubling B halves A, tripling B decreases A by 1/3, etc.;

• A µ 1/B3 means A is inversely proportional to B cubed. An increase in B results in a large decrease in A. Doubling B decreases A by 1/23 = 1/8.

Exercises - First in words:

  1. Acceleration is _______________________ to the force applied.

  2. For a fixed force, the acceleration of an object is _________________________ to the mass of the object.

  3. The force of gravity between Mars and it moon Deimos is ________________________ to the product of the masses of Mars and Deimos and is _________________________ to the distance between their centers _____________.

  4. On the Moon, the acceleration of an object due to the gravity of the Moon is proportional to the mass of ________________ and independent of the mass of ______________ .

  5. The orbital velocity of the Galileo spacecraft in (roughly circular) orbit around Jupiter is proportional to the square root of the mass of _____________________ and inversely proportional to the square root of ____________________________.

Now in numbers:

  1. The force of gravity on the surface of planet Blob is 2.8 times the force of gravity on planet Blip. If you drop a hammer on these two planets the acceleration of the hammer will be ______ times greater on planet ________.

  2. You have 2 identical bottle rockets (fireworks). When you ignite one bottle rocket the chemicals in the firework provide a force which accelerates it into the air. Next, you tie a squirrel onto the 2nd bottle rocket, which triples the mass of the rocket. When you ignite the second rocket the acceleration of the 2nd rock is __________ times the acceleration of the 1st rocket.

(2) Newton's Laws. Fill in the blanks using the list of words below.

    Isaac Newton developed, among other things, three laws to explain motion and one law to describe gravity. His first law describes the nature of motion of an object , stating that if an object is at rest it will remain at __________ . If an object is in motion, it will _______ in motion at the _______ speed and _________, until it is acted upon by a __________. According to Newton's second law, the _____________ of a body is _____________ to the force acting on the body. Furthermore, the ____________ of the body is in the ___________ direction as the force acting on it. Newton's third law says that if a force is applied to an object, the object exerts a _________, _________ in size to the original ________ and in the __________ direction on the first body. Newton explained the nature of gravity in his law of gravitation, which states that the force of gravity between two objects is ____________ to the _________ of the objects and ___________ proportional to the ___________ of the distance between them.

acceleration equal distance
cube square bodies
force different opposite
masses action reaction
rest same change
direction proportional inversely
continue motion always

 

(3)The Law of Gravitation. Use Newton's universal law of gravitation to answer each of the following questions.

(a) How does tripling of the distance betwen two objects affect the graviational force between them?

(b) Compare the graviational force between the Earth and Sun to that between Jupiter and the Sun. (Jupiter has a mass 318 times the mass of the Earth and orbits at a distance of 5.2 AU from the Sun. Hint: the word "compare" is a strong clue that you should calculate a ratio - in this case a ratio of the Sun-Earth force to the Sun-Jupiter force).

 

 

 

 

(c) Suppose the Sun were magically replaced by a star with twice as much mass. What would happen to the gravitational force between the Earth and the Sun?

 

(5) Map of the Solar System. For the following appearances of the planets, locate and label their positions on a map of the solar system.

Mercury is visible in the sky in the evening after sunset,

Venus is visible in the morning before sunrise,

and Mars is visible high in the sky at midnight.

(Hint: draw concentric circles for the planetary orbits with the Sun in the middle. Put in the Earth. Think about how the Earth spins - where are you on the Earth at noon, midnight, dawn, dusk...). Now add Mercury, Venus and Mars to the diagram.

 

 

 

 

 

 

 

 

 

(6) You are an astronaut on the Moon in the year 2020 AD, working at Lunar Base 1 in Mare Serenitatis (near the center of hemisphere that faces Earth). Describe any apparent motion and any changes in appearance of the Earth that you observe (hour by hour, day to day, month to month - over the year - say).