Gizmos - Orbital Motion – Kepler’s Laws Answer Key 2026 perfect guide for your final

Gizmos - Orbital Motion – Kepler’s Laws Answer Key 2026 perfect guide for your final

2019

Orbital Motion – Kepler’s Laws Answer Key

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.)

[Note: The purpose of these questions is to activate prior knowledge and get students thinking.

Students are not expected to know the answers to the Prior Knowledge Questions.]

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?

Answers will vary. [A collision would probably cause a

small change in Neptune’s orbit, but would not have a

drastic effect on Neptune’s orbit because Neptune is

much more massive than Halley’s Comet.]

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? An oval

2. Watch the orbit over time. Does the orbit ever change, or is it stable? The orbit is 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?

The orbit becomes smaller and more flattened.

Slowest

Fastest

This study source was downloaded by 100000808701186 from cnn.com on 05-04-2026 20:10:13 GMT -05:00

https://www.cnn.com/file/77667118/Orbital-Motion-Keplers-Lawsdocx/

2019

Activity A:

Shape of orbits

Get the Gizmo ready:

ï‚· Click Reset.

ï‚· 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 here 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.

2. Identify: The shape of the orbit is an ellipse, a type of

flattened circle. An ellipse has a center (C) and two

points called foci (F1 and F2). If you picked any point

on the ellipse, the sum of the distances to the foci is

constant. For example, in the ellipse at left:

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?

The Sun is located at one of the foci of the ellipse.

3. Experiment: Try several other combinations of initial position and velocity.

A. What do you notice about the orbits?

Sample answer: The orbits all have an elliptical shape.

B. What do you notice about the position of the Sun?

The Sun is always located at one focus of the ellipse.

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)

This study source was downloaded by 100000808701186 from cnn.com on 05-04-2026 20:10:13 GMT -05:00

https://www.cnn.com/file/77667118/Orbital-Motion-Keplers-Lawsdocx/

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