Student Exploration: Orbital Motion – Kepler’s Laws
Vocabulary: astronomical unit, A unit of measurement that is equal to 149.6 million km.
eccentricity, Measurement of how flat an orbit is.
ellipse, Flattened circle
force, action that causes an object to shift
gravity, force that acts on other bodies to pull them in.
Kepler’s first law, Planets travel around the sun in elliptical orbits.
Kepler’s second law, Planets accelerate when they near the sun, and decelerate when the move away from it.
Kepler’s third law, Cube of planets orbital radius is proportional to its period.
orbit, curved revolution of object around a planet, moon, or star.
orbital radius, the average orbit distance from the sun
period, Length of time
vector, A quantity.
velocity, speed and direction
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
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.
How might a collision between Neptune and Halley’s Comet affect Neptune’s orbit?
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 ().
What is the shape of the planet’s orbit?
Watch the orbit over time. Does the orbit ever change, or is it stable?
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?