Download Hubble Law Worksheet

Hubble’s Law Activity
Materials:
-A thick rubber band (1/4 in or so) and a pair of scissors
-A set of small colored paper clips
-Thumbtacks
-A board the thumbtacks can stick into (Anything that works: cork, wood,
foam board, etc.)
-A ruler
-Graph paper
Procedure:
1) Cut the rubber band and put the colored paper clips at different positions along it. Pick any
positions you want (its better if they are not evenly spaced). Leave a length of rubber band at
each end. You should end up with something that looks like this (You don’t have to use 8
paper clips as shown, less will do. They should each be different colors, though)
You have just created a one-dimensional universe: each paper clip is a galaxy at some point in
“space”.
2) Using the thumbtacks, attach the rubber band to your board so that the rubber band is
stretched slightly so that it is taut. Pick one of the galaxies to be the Milky Way (MW), say
the pink one. Using you ruler measure the distance between the MW clip to each of the others
clips. (It doesn’t matter if a clip is left or right or your MW clip; all distances are positive)
Record your measurements in a table like this
Red
Distance
from MW
Pink
(MW)
0
Green
Purple
Orange
You now have galactic distances in the your Universe at some time
Blue
3) Now, untack your rubber band, stretches it a decent amount, and tack it back down again.
Repeat step 2), measuring the new (larger) distances between the MW clip and all the others.
Your table should now have a new row
Red
Distance
from MW
New
distance
from MW
Pink
(MW)
0
Green
Purple
Orange
Blue
0
By stretching the rubber band you have caused your Universe to expand, resulting in the galaxy
distances increases. You now have galactic distances in your Universe at a later time.
4) Calculate how much the distances from the MW clip have increased by subtracting the
numbers in row 1 from the numbers in row 2. Put this value in a new row labeled velocity.
Red
Distance
form Mw
New
distance
from MW
Velocity
Pink
(MW)
0
Green
Purple
Orange
Blue
0
0
Why velocity? We can use the distance change of each clip to represent the velocity of the clip as
seen from the MW clip. Since we don’t how long the “expansion” of your universe took, we can’t
convert the distance change to a velocity as it is normally measured, say, cm/sec. But no matter
what the time difference, the distance difference will still be proportional to the “recession”
velocity.
5) Using the graph paper, make a plot of velocity (fourth row data) on the y-axis and distance
(second row data) on the x-axis.
Discussions Questions:
Does it look like the points fall on a straight line?
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Describe how your plot is a 1-dimensional representation of Hubble’s Law.
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6) Now, let’s look at another galaxy. Pick a different clip (say the orange one) other than the
MW clip and repeat steps 2) through 5).
Discussion Questions:
Do the points fall on a straight line for this “galaxy”
I
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Do you expect the data from the “Alien” galaxy to also show a version of Hubble’s Law?
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7) Now plot the data from your MW clip and your “other galaxy” clip on the same graph to see
how they compare.
Discussion Questions:
How do the two set of data compare? ___________________________________
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Do the Milky Way data and the “Alien” galaxy data fall on the same line?
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What would be the reason for two “Hubble Laws” to agree exactly? What does this tell us
about our Universe?
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