Inertia and GravityInertia and Gravity

Activity One Marble LabActivity One Marble Lab Activity 1Activity 1 Place the marble on the paper in the tray. Invert the Place the marble on the paper in the tray. Invert the

plastic cup over the marble.plastic cup over the marble. Move the cup in a rapid circular motion, causing the Move the cup in a rapid circular motion, causing the

marble to move around the inside edge of the cup.marble to move around the inside edge of the cup. While the marble is moving rapidly in the cup, lift the cup While the marble is moving rapidly in the cup, lift the cup

straight up off the paper.straight up off the paper. Record in your journal what happens to the marble.Record in your journal what happens to the marble. Repeat the activity, paying careful attention to the path of Repeat the activity, paying careful attention to the path of

the marble takes after lifting the cup.the marble takes after lifting the cup. Explain the marble’s motion.Explain the marble’s motion. Draw an explanation of the marble’s motion in your Draw an explanation of the marble’s motion in your

journal; be sure to label the drawing. (Cup, Marble and journal; be sure to label the drawing. (Cup, Marble and Path of the marblePath of the marble

Marble Lab Questions to discussMarble Lab Questions to discuss

Marble lab after looking at all illustrations.Marble lab after looking at all illustrations. 1. What do all of the illustrations have in 1. What do all of the illustrations have in

common?common? 2. What kept the marble moving in a circular 2. What kept the marble moving in a circular

pattern?pattern? 3. Inertia is an object’s resistance to a change 3. Inertia is an object’s resistance to a change

in its motion. This means objects at rest will stay in its motion. This means objects at rest will stay at rest, and objects that are moving will continue at rest, and objects that are moving will continue to move in a straight line unless they are acted to move in a straight line unless they are acted on by an unbalance force. How does the on by an unbalance force. How does the concept of inertia apply to this activity?concept of inertia apply to this activity?

Spinning Sphere labSpinning Sphere lab

Activity 2Activity 2 Watch the teacher demonstration.Watch the teacher demonstration. Read the slides on Inertia and Gravity.Read the slides on Inertia and Gravity. Answer following questions: Planet MotionAnswer following questions: Planet Motion

Describe how the planets are kept in motion within their Describe how the planets are kept in motion within their orbit.orbit.

Describe the role of inertia plays in keeping the planets Describe the role of inertia plays in keeping the planets within their orbit.within their orbit.

Describe how Newton’s law of the universal gravitational Describe how Newton’s law of the universal gravitational applies to the motion of the planets in our solar system.applies to the motion of the planets in our solar system.

Draw diagram in your journal of the Orbit of a planet.Draw diagram in your journal of the Orbit of a planet.

Spinning Sphere QuestionsSpinning Sphere Questions

1. What does the ball represent in this 1. What does the ball represent in this model?model?

2. What do the washers represent?2. What do the washers represent? 3.What happens when we whirl the model 3.What happens when we whirl the model

faster?faster? 4. When we whirl the model, what allows 4. When we whirl the model, what allows

the ball to remain in a circular pattern?the ball to remain in a circular pattern? 5. What would happen if we let go of the 5. What would happen if we let go of the

ball?ball?

More QuestionsMore Questions

6. What is a force?6. What is a force? 7. Gravity is a pulling force. How is gravity 7. Gravity is a pulling force. How is gravity

represented in this model?represented in this model? 8. How is the concept of gravity applied to 8. How is the concept of gravity applied to

the Sun and planet?the Sun and planet? 9. What would happen if there was not 9. What would happen if there was not

gravity between the planets and the Sun?gravity between the planets and the Sun?

Early Greek and Roman Early Greek and Roman observationsobservations

Early Greek and Roman astronomers Early Greek and Roman astronomers were the first to observe that planets seem were the first to observe that planets seem to move around in the sky while stars to move around in the sky while stars appear to be more stationary in their appear to be more stationary in their positions. In fact, the word positions. In fact, the word planetplanet comes comes from the Greek word from the Greek word planasthaiplanasthai, which , which means “to wander.”means “to wander.”

Johannes KeplerJohannes Kepler

During the 1600s, a German astronomer During the 1600s, a German astronomer named Johannes Kepler made careful named Johannes Kepler made careful observations of planets and their observations of planets and their movements around the Sun. Kepler movements around the Sun. Kepler discovered that planets travel around the discovered that planets travel around the Sun in a particular path called an orbit. Sun in a particular path called an orbit. One complete orbital path around the Sun One complete orbital path around the Sun is a revolution.is a revolution.

Sir Isaac NewtonSir Isaac Newton

Later during the same century, Sir Isaac Later during the same century, Sir Isaac Newton made several discoveries that Newton made several discoveries that helped explain Kepler’s observation about helped explain Kepler’s observation about the orbits of planets. Newton’s law of the orbits of planets. Newton’s law of universal gravitation states that every universal gravitation states that every object in the universe attracts every other object in the universe attracts every other object.object.

Two Important Factors:Two Important Factors:

How strongly objects pull on each other How strongly objects pull on each other depends upon two factors:depends upon two factors:

1.1. How much matter the objects have How much matter the objects have (mass)(mass)

2.2. How far apart the objects are (distance)How far apart the objects are (distance)

InertiaInertia

The Sun has a gravitational pull on The Sun has a gravitational pull on planets. Inertia is an objects resistance to planets. Inertia is an objects resistance to any change in its motion. Objects at rest any change in its motion. Objects at rest will stay at rest, and objects moving will will stay at rest, and objects moving will continue to move in a straight line unless continue to move in a straight line unless they are acted on by an unbalanced force. they are acted on by an unbalanced force. Without the gravitational force between the Without the gravitational force between the Sun and the planet, the planet would travel Sun and the planet, the planet would travel off into space in a straight line, (like your off into space in a straight line, (like your marbel did)marbel did)

The Sun gravitational Pulls causes The Sun gravitational Pulls causes Planets to orbit.Planets to orbit.

Each planet continues to move forward Each planet continues to move forward because of its inertia, but due to the force because of its inertia, but due to the force of gravity, the planet travels in a curved of gravity, the planet travels in a curved orbit.orbit.

Select one of the following to write Select one of the following to write about in your journalabout in your journal

1. Describe how the planets are kept in 1. Describe how the planets are kept in motion within their orbit.motion within their orbit.

2. Describe the role inertia plays in 2. Describe the role inertia plays in keeping planets within their orbit.keeping planets within their orbit.

3. Describe how Newton’s Law of 3. Describe how Newton’s Law of universal gravitation applies to the motion universal gravitation applies to the motion of the planets in our solar system.of the planets in our solar system.

Location in Location in Solar SystemSolar System

Gravity at Surface Gravity at Surface (When Earth=1)(When Earth=1)

Weight at Weight at Given LocationGiven Location

SunSun 27.927.9 27902790

MercuryMercury 0.370.37

VenusVenus 0.880.88

EarthEarth 1.001.00

Earth’s MoonEarth’s Moon 0.170.17

MarsMars 0.380.38

JupiterJupiter 2.132.13

SaturnSaturn 0.740.74

UranusUranus 0.860.86

NeptuneNeptune 1.071.07* Multiply the number by 100 N

Weight in the Solar System

• Based on the table, at which location in the solar system will the object weigh the most?

• Based on the table, at which location will the same object weigh the least?

• How does changing the location of the object affect the mass of the object?

• How does changing the force of gravity pulling on an object affect its mass?