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eraemia
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Homework Statement
Each part of this problem describes an object in a specific physical context in which it interacts with other objects. In each case, use the macroscopic interaction categories to list the ways that the object interacts with its surroundings; and for each listed interaction, state the other object involved. Remember that an interaction, if unopposed, will act to change the object’s velocity, but two opposed interactions may cancel each other’s effect on the velocity. Do the best you can; some of these are hard! >_<
0) A hockey puck sliding on rough ice
a) A person sits on a chair.
b) A leaf falls from a tree. (Consider the leaf after it has left the tree
c) A magnet sticks to the side of a refrigerator.
d) A tiny bit of paper jumps from a tabletop toward an electrically charged comb. (Consider the bit after it has left the tabletop but before it reaches the comb.)
e) Difficult: A child hangs on to a playground merry-go-round that is rotating so rapidly that the child is suspended above the ground. (ignore air friction)
f) Difficult: A car accelerates down a road. We will see later in this unit that processes internal to an object can never change the motion of the object as a whole: only an interaction with something external can do this. If this is so, what interaction increases the car’s speed? Would the acceleration be possible if the road were very slippery?
Homework Equations
Macroscopic Interactions (2 categories)
A. Long-range interactions—that allow objects to influence one another over significant distance
1) Electrostatic interactions—involve at least one electrically
charged object
2) Magnetic interactions—involve at least one magnet
3) Gravitational interactions
B. Contact interactions—arise only when objects come into direct physical contact
1) Friction interactions—oppose the relative motion of the
objects in contact
2) Compression interactions—seek to keep them from merging
3) Tension interactions—oppose their separation
The Attempt at a Solution
a) A person sits on a chair.
Long-range: Gravitational interaction: Between the Earth and both the chair and the person
Contact: Compression interaction: Between the chair and the person
Is there any friction or electrostatic interaction occurring here?
b) A leaf falls from a tree. (Consider the leaf after it has left the tree but before it hits the ground.)
Long range: Gravitational interaction: Between Earth and leaf
Contact: Friction interaction: Between air and leaf
Contact: Compression interaction: Between air and leaf
c) A magnet sticks to the side of a refrigerator.
Long-range: Magnetic interaction: Between magnet and refrigerator
Long-range: Gravitational interaction: Between Earth and both magnet and refrigerator
Contact: ?
d) A tiny bit of paper jumps from a tabletop toward an electrically charged comb. (Consider the bit after it has left the tabletop but before it reaches the comb.)
Long-range: Electrostatic interaction
Long-range: Gravitational
?
e) Difficult: A child hangs on to a playground merry-go-round that is rotating so rapidly that the child is suspended above the ground. (ignore air friction)
Long-range: Gravitational
f) Difficult: A car accelerates down a road. We will see later in this unit that processes internal to an object can never change the motion of the object as a whole: only an interaction with something external can do this. If this is so, what interaction increases the car’s speed? Would the acceleration be possible if the road were very slippery?
Long-range: Gravitational
I don't understand this one at all...
Thanks for the help, everyone.