The Universe - Can You Throw a Football to Venus?

Your challenge will be to demonstrate how large the solar system is. This activity allows you to model this solar system outdoors. Each person who participates will take a turn acting as the sun. This person has the football challenge ... can you throw the football all the way to Venus? Make it a contest between your friends!

Materials:

• At least ten friends or classmates
• Ruler or meter stick
• Football

Procedure:

1. Assign one person from your group to act as the sun.
2. Assign each other person in the group to act as a different planet.
3. Have the person representing the sun stand in one place and begin to measure the distance from the sun to each planet.
4. Use the information from the chart below for your measurements.
5. The chart shows the distances from the sun to each planet. Distances are given in a unit called Astronomical Units (AU). One AU is the distance from the sun to Earth.
6. To make this model as accurate as possible, have one AU equal to one meter.

 Planet Approximate Distance from Sun (AU) Mercury 0.3 Venus 0.7 Earth 1.0 Mars 1.5 Jupiter 5.2 Saturn 9.5 Uranus 19.8 Venus 30.6
7. Have your friends, who are representing planets, line up in a straight line going away from the sun.
8. Now for the challenge!
• The person representing the sun is to throw a football to Venus.
• Rotate each person in one planet (with the person representing Mercury going to the sun position.)
• Repeat the challenge
9. The person who gets the football to the farthest planet wins.

Analysis:

1. How far away from the sun is Venus?
2. What was the farthest planet to which each person was able to throw the football?
3. Why was it difficult to throw the football beyond Venus, the last planet in the solar system?
4. Alpha Centauri is the closest star outside of our solar system. If you were to try to throw a football to this star, you would need to throw it over 273 kilometers (164 miles). How many Astronomical Units is that?

So what keeps the Universe together?

If the solar system is so large, what keeps it all together? You already read about how the heat of the early sun caused the differences between the inner and outer planets. However, what keeps those planets in orbit around the sun? Two primary forces act together to keep the planets in orbit.

Thanks to the work of Isaac Newton in the 1600's, we have a much better understanding of how the solar system works. Newton is well-known for developing his three laws of motion, one of which states that an object in motion tends to stay in motion at the same velocity unless acted on by an outside force. The characteristic of an object to do that is called inertia. You experienced this when you were in a car and go around a corner. Your body tries to keep moving in the same direction it was, but the seat belt or side of the car makes you change your direction.

Inertia is only one of the significant reasons for the solar system shape. There must be some sort of outside force causing the planets to change direction instead of traveling in a straight line. That other force is called gravity. You are probably familiar with the story of Newton watching an apple fall from the apple tree and developing what is called the Law of Universal Gravitation. He stated that every object in the universe is attracted to the all other objects. The strength of that attraction depends on the mass of the objects and the distance between them. This gravitational attraction is what opposes the inertia of the planets and keeps them from flying off into space in a straight line.

An easy way to illustrate this is to tie a ball to the end of a string or a rope. Twirl the ball above your head in a circle. Experiment with different lengths of rope between you and the ball. Watch the video below to see an example.

Analysis:

1. Why does the solar system look the way it does?
2. Describe at least two ways the inner are different from the outer planets?
3. What caused those differences?
4. Why is Newton credited with developing the Law of Universal Gravitation?
5. What relationship does inertia play in keeping a planet in orbit?
6. Describe the role of gravity in Earth's revolution around the Sun?
7. In the video example, what does the rope attached to the ball represent?
• What would happen if the ball was released?
• How does this example model the motion of the planets?