Name: 2022
Student Exploration: Orbital Motion – Kepler’s Laws
Vocabulary: astronomical unit, eccentricity, ellipse, force, gravity, Kepler’s first law, Kepler’s
second law, Kepler’s third law, orbit, orbital radius, period, vector, velocity
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. The orbit of Halley’s Comet, shown at right, has an oval
shape. In which part of its orbit do you think Halley’s
Comet travels fastest? Slowest? Mark these points on
the diagram at right.
2. How might a collision between Neptune and Halley’s
Comet affect Neptune’s orbit?
It will run it off its course.
Gizmo Warm-up
The path of each planet around the Sun is determined by
two factors: its current velocity (speed and direction) and
the force of gravity on the planet. You can manipulate both
of these factors as you investigate planetary orbits in the
Orbital Motion – Kepler’s Laws Gizmo™.
On the CONTROLS pane of the Gizmo, turn on Show trails
and check that Show vectors is on. Click Play ( ).
1. What is the shape of the planet’s orbit? A circle
2. Watch the orbit over time. Does the orbit ever change, or is it stable? Stable
3. Click Reset ( ). Drag the tip of the purple arrow to shorten it and reduce the planet’s
initial velocity. Click Play. How does this affect the shape of the orbit?
It is now really smaller and its more in the shape of a oval
, Get the Gizmo ready:
Activity A:
● Click Reset.
Shape of orbits ● Turn on Show grid.
Introduction: The velocity of a planet is represented by an arrow called a vector. The vector is
described by two components: the i component represents east-west speed and the j
component represents north-south speed. The unit of speed is kilometers per second (km/s).
Question: How do we describe the shape of an orbit?
1. Sketch: The distance unit used her is the astronomical
unit (AU), equal to the average Earth-Sun distance.
Place the planet on the i axis at r = –3.00i AU. Move the
velocity vector so that v = -8.0j km/s (|v| = 8.00 km/s).
The resulting vectors should look like the vectors in the
image at right. (Vectors do not have to be exact.)
Click Play, and then click Pause ( ) after one
revolution. Sketch the resulting orbit on the grid.
INCLUDEPICTURE
"http://www.explorelearning.co
m/ELContent/gizmos/ELScienc 2. Identify: The shape of the orbit is an ellipse, a type of
e_Deliverable/ExplorationGuide flattened circle. An ellipse has a center (C) and two
s/images/EL_MSPS_OrbitKeple points called foci (F1 and F2). If you picked any point
r1.gif" \* MERGEFORMATINET on the ellipse, the sum of the distances to the foci is
constant. For example, in the ellipse at right:
a1 + a2 = b1 + b2
Turn on Show foci and center. The center is represented by a red dot, and the foci are
shown by two blue dots. What do you notice about the position of the Sun?
It is diagonal towards them
3. Experiment: Try several other combinations of initial position and velocity.
A. What do you notice about the orbits? The bigger the purple lie is the bigger the circle
is
B. What do you notice about the position of the Sun? It stays the same
You have just demonstrated Kepler’s first law, one of three laws discovered by the German
astronomer Johannes Kepler (1571–1630). Kepler’s first law states that planets travel
around the Sun in elliptical orbits with the Sun at one focus of the ellipse.
(Activity A continued on next page)
Student Exploration: Orbital Motion – Kepler’s Laws
Vocabulary: astronomical unit, eccentricity, ellipse, force, gravity, Kepler’s first law, Kepler’s
second law, Kepler’s third law, orbit, orbital radius, period, vector, velocity
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. The orbit of Halley’s Comet, shown at right, has an oval
shape. In which part of its orbit do you think Halley’s
Comet travels fastest? Slowest? Mark these points on
the diagram at right.
2. How might a collision between Neptune and Halley’s
Comet affect Neptune’s orbit?
It will run it off its course.
Gizmo Warm-up
The path of each planet around the Sun is determined by
two factors: its current velocity (speed and direction) and
the force of gravity on the planet. You can manipulate both
of these factors as you investigate planetary orbits in the
Orbital Motion – Kepler’s Laws Gizmo™.
On the CONTROLS pane of the Gizmo, turn on Show trails
and check that Show vectors is on. Click Play ( ).
1. What is the shape of the planet’s orbit? A circle
2. Watch the orbit over time. Does the orbit ever change, or is it stable? Stable
3. Click Reset ( ). Drag the tip of the purple arrow to shorten it and reduce the planet’s
initial velocity. Click Play. How does this affect the shape of the orbit?
It is now really smaller and its more in the shape of a oval
, Get the Gizmo ready:
Activity A:
● Click Reset.
Shape of orbits ● Turn on Show grid.
Introduction: The velocity of a planet is represented by an arrow called a vector. The vector is
described by two components: the i component represents east-west speed and the j
component represents north-south speed. The unit of speed is kilometers per second (km/s).
Question: How do we describe the shape of an orbit?
1. Sketch: The distance unit used her is the astronomical
unit (AU), equal to the average Earth-Sun distance.
Place the planet on the i axis at r = –3.00i AU. Move the
velocity vector so that v = -8.0j km/s (|v| = 8.00 km/s).
The resulting vectors should look like the vectors in the
image at right. (Vectors do not have to be exact.)
Click Play, and then click Pause ( ) after one
revolution. Sketch the resulting orbit on the grid.
INCLUDEPICTURE
"http://www.explorelearning.co
m/ELContent/gizmos/ELScienc 2. Identify: The shape of the orbit is an ellipse, a type of
e_Deliverable/ExplorationGuide flattened circle. An ellipse has a center (C) and two
s/images/EL_MSPS_OrbitKeple points called foci (F1 and F2). If you picked any point
r1.gif" \* MERGEFORMATINET on the ellipse, the sum of the distances to the foci is
constant. For example, in the ellipse at right:
a1 + a2 = b1 + b2
Turn on Show foci and center. The center is represented by a red dot, and the foci are
shown by two blue dots. What do you notice about the position of the Sun?
It is diagonal towards them
3. Experiment: Try several other combinations of initial position and velocity.
A. What do you notice about the orbits? The bigger the purple lie is the bigger the circle
is
B. What do you notice about the position of the Sun? It stays the same
You have just demonstrated Kepler’s first law, one of three laws discovered by the German
astronomer Johannes Kepler (1571–1630). Kepler’s first law states that planets travel
around the Sun in elliptical orbits with the Sun at one focus of the ellipse.
(Activity A continued on next page)
