Name _______________________________ Date ______________
Construct Planetary Orbits Around the Sun
Student Activity Sheet
Materials:
thumbtacks or pins, string, cardboard (21.5 cm x 28 cm), metric ruler, pencil,
paper, calculator.
Purpose:
In this activity student will learn how to make an ellipse using string and how
varying the length of the string alters the shape of the ellipse. Students will
also learn how characteristics of an ellipse relate to the orbits of the planets.
Procedure:
Part A
1. Place a blank sheet of paper on top of the cardboard and place two
thumbtacks or pins about 3 cm apart.
2. Tie the string into a circle with a circumference of 15 to 20 cm. Loop the
string around the thumbtacks. With someone holding the tacks or pins,
place a pencil inside the loop and pull it taut.
3. Move the pen or pencil around the tacks, keeping the string taut, until
you have completed a smooth, closed curve or an ellipse.
4. Repeat Steps 1 though 3 several times. First vary the distance between
the tacks and then vary the circumference of the string. However,
change only one of these each time. Note the effect on the size and
shape of the ellipse with each of these changes.
5. Orbits are usually described in terms of eccentricity (e) The eccentricity
of any ellipse is determined by dividing the distance ( d ) between the
foci or tacks by the length of the major axis (L). Measure and record (d)
and (L) for each ellipse you created.
6. Calculate and record the eccentricity of the ellipses that you
constructed.
Part B
