Day 3: Newton’s Universe

Time in History:

25 December 1642 – 20 March 1727

Question of the Day:

What concept was central to Newton’s explanation of planetary motion?

Key Concepts

Lesson of the Day

Sir Isaac Newton is considered one of the greatest scientists of all time. Newton was born in England the year of Galileo’s death. His father died before he was born, and he was raised by his mother and grandparents. His mother hoped he would become a farmer, but he hated farming and managed to find his way to Trinity College, Cambridge. In Newton’s time the course of study at Cambridge was based on the work of Aristotle, which Newton supplemented with the readings of Galileo and Kepler among other ‘modern philosophers’.

Although an average student at Cambridge during his final year of study and the subsequent two years following his formal education his private studies at home lead him to develop or discover

Not bad production for a few short years.

Popular legend has it that Newton was sitting under an Apple Tree when falling apple struck him on the head precipitating the conception of the theory a gravity. As Newton’s colleague British scientist William Stukeley relates in the following reminiscence, apparently an apple tree was involved in the birth of the notion of gravity:

“... we went into the garden, & drank thea under the shade of some appletrees; only he, & my self. Amidst other discourse, he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. "Why should that apple always descend perpendicularly to the ground," thought he to himself; occasion'd by the fall of an apple, as he sat in a contemplative mood. "Why should it not go sideways, or upwards? But constantly to the earths center? Assuredly, the reason is, that the earth draws it. There must be a drawing power in matter & the sum of the drawing power in the matter of the earth must be in the earths center, not in any side of the earth. Therefore dos this apple fall perpendicularly, or toward the center. If matter thus draws matter; it must be in proportion of its quantity. Therefore the apple draws the earth, as well as the earth draws the apple."

Considering these observations, Newton developed three universal laws of motion that he published in his most famous work, the Principia, in 1687. The laws of motion were unique in that they provided a universal explanation for how objects, both on earth and in space moved. These laws helped outline Newton’s theory of gravity. Then, referencing Kepler’s work he applied his laws of motion and concept of gravity to the orbits of the planets, suggesting that the gravitational pull of the sun explained the motion of planets in our solar system. He supported this suggestion by establishing a mathematical proof that the elliptical orbit of planets suggested by Kepler resulted from a centripetal gravitational force inversely proportional to the square of the radius vector of each planet.

Newton’s contribution modernized the understanding of how celestial bodies move and interrelate. Any vestiges of belief in a heliocentric solar system were abandoned after Newton’s mathematical proofs of the universal law of gravity and its effect on the motion of planets.

Origin Story of the Day:

A long time ago there was a Mohawk village of bark houses along the Oswego River. One day Mohawk hunters discovered the tracks of a Giant Bear. After that, they saw the tracks many times. Sometimes, the tracks would circle the Mohawk village. The animals began to disappear from the forests, and the Mohawks knew that the Giant Bear was killing and carrying off all the animals.

Because of the scarcity of food, famine came to the Mohawks. The meat racks were empty. The people were hungry. Starvation tempted them. One of the chiefs said, "We must kill this Giant Bear who is causing all our trouble." At once a party of warriors set out in search of the bear. They soon came across his tracks in the snow. They followed the bear tracks for many days. They finally came upon the huge beast. At once the air was filled with the arrows of the warriors. To the surprise and dismay of the Mohawks, the arrows failed to pierce the thick hide of the bear. Many broken arrows fell from his tough skin.

At last the angry bear turned and charged the hunters who fled but were soon overtaken. Most of them were killed. Only two hunters escaped and they returned to the village to tell the sad tale. The two hunters told the council of the Great Bear. They told what happened to the war party.

Party after party of warriors set out to destroy the Great Bear but they always failed. There were many battles fought between the bear and the warriors. Many warriors were slain.

As time went on, more and more deer vanished from the forest. The smoking racks were empty. The people became very thin because of the lack of food. Starvation caused many to become sick. The people were filled with fear and their hungry bodies crept close to the fire at night. They feared the Great Bear, whose giant tracks circled their town each night. They feared to leave their village because they could hear, coming from the darkness of the forest, the loud cough of the Great Bear.

One night three brothers each had a strange dream. On three successive nights, they had the same vision. They dreamed they tracked and killed the Great Bear. They said, "The dream must be true."

So, getting their weapons and scanty supply of food, they set out after the bear. In a little while, they came upon the tracks of the great beast. Quickly, they followed the trail, their arrows ready.

For many moons they followed the tracks of the bear across the Earth. The tracks led them to the end of the world. Looking ahead, they saw the giant beast leap from the earth into the heavens. The three hunters soon came to the jumping-off place. Without hesitation, the three of them followed the bear into the sky. There in the skis, you can see them chasing the bear during the long winter nights.

In the fall of the year, when the bear gets ready to sleep for the winter, the three hunters get near enough to shoot their arrows into his body. His dripping blood caused by the wounds from the arrows turn the autumn leaves red and yellow. But he always manages to escape from the hunters. For a time, after being wounded, he is invisible. He afterwards reappears.

When the Iroquois see the Great Dipper in the sky, they say, "See, the three hunters are still chasing the Great Bear!"

School Activity:

Newton's Laws of Motion Activities:


Students can estimate the mass of a car by doing a simple experiment, under adult supervision of course. You'll need a car, level ground, bathroom scales, chalk, measuring tape, and stopwatches. Have three strong students push the car. They will push the car from behind with the bathroom scales between their hands and the car. Their goal is to push the car with as constant a force—measured by the reading on the scale—as possible.

Another student sits in the driver's seat to steer and operate the brake. A fifth student sits in the front passenger seat and marks chalk lines on the ground at regular time intervals. A sixth student sits in the back, calling out "mark" every two seconds, after the "ready, set, go" has been announced. From the changing distance traveled in each time increment, students can calculate the car's acceleration. You can find the speed over each interval, then look at how it changes over the set of intervals. With the force measured from the bathroom scales, and the acceleration, students can then estimate the car's mass using F=ma. When finished, the estimate of the car's mass can be checked by looking at the posted mass on the doorframe of the driver's side, or by searching the Internet. Ask the students to brainstorm the various possible sources of error in the experiment. You can also film this for later video analysis.


If you have access to a gymnasium or open space, have students race to see who can have the most constant acceleration. You'll need ten students, each with their own stopwatch, to stand at ten-meter (or yard) intervals. When the starter says "go" the timers start timing and the runner runs down the track. As she passes each timer, that person stops the stopwatch. A recorder then gathers the times from each timer.

Have five or so students run, and then ask the class to find each runner's average speed over each ten-yard interval. Have them graph this average speed versus time and look at the slope of the curve. The curve with the most constant slope (closest to a diagonal line) will be the person with the most consistent acceleration, and the winner of the race.

Discovering Color With a Prism

The student will observe what happens to light as it passes through a prism. The student will experiment with white light that is composed of a continuous band of colors. The band of colors appears in the same pattern as the colors of a rainbow.

This experiment was first done by Sir Isaac Newton (1642–1727). Newton let a beam of sunlight pass through a glass prism and observed the white light spectrum. In a vacuum, light of all colors travels at the same speed. When light passes through a material, such as glass or water, the red light at one end of the spectrum travels faster than the violet light at the other end of the spectrum. This difference in speed causes a change in the direction of light when going from air to glass and from glass to air. This change of direction is called refraction, and is greater for violet light than for red light. The speed of light in the glass depends on the color; thus we get a continuous band as in the rainbow.


1. Hold the small prism with one finger at the top and one finger at the bottom. Position the prism 2 to 3 inches in front of your eye. Look through one side of it in the direction of the light source as shown below.

2. First, look at the incandescent lamp. Observe the colors that are visible as you view this lamp.

3. Next, view the fluorescent lamp and then the cadmium lamp. (The kinds of light source may vary.)

4. Record your observations below.

Light Source Colors
Observations, Data, and Conclusions

1. Observe the colors from the three different light sources and list them in order in the chart below. Start with the first color on the left and list them as you see them. (Hint: ROY G. BIV—red, orange, yellow, green, blue, indigo, violet)

2. What differences and/or similarities did you observe in each light source when looking through the glass, plastic or acrylic plastic?

3. Were the colors always in the same order?

4. Were the colors always in bands?

5. Did the bands always form the same shapes?

Hint: An artificial light source will not transmit the complete spectrum unless it is a white light source.