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Activity 2: Speed & Gravity

Dinama Stabenstein

ALL ABOUT SPEED

Summary:

The only way to escape the gravity of an object is through high velocity (speed). With water in a bucket students will see if they can escape gravity.

(This activity will also demonstrate centrifugal and centripetal forces as well as inertia, which are all properties of mass, though we do not address them directly in the GEODETECTIVE Curricula).

Instructional Method:

Experiment

Goal:

To understand how speed can allow an object to escape gravity.

Objective:

Students will be able to see how speed can cause objects to defy gravity

Time:

1 hour, this is recommended as an outdoor activity.

Materials Needed:

  • Bucket, one for each group
  • Water to partially fill the bucket
  • Rain ponchos or garbage bags to keep kids dry

Vocabulary:

gravity
orbit
satellite
speed
centrifugal forces
centripetal forces

Background:

Gravity is in everything and acts on everything, including water in a bucket. The sun is always pulling on the Earth, which makes us wonder, "Why don't we get pulled into the sun?" The answer is speed. Earth is moving too fast, or just fast enough, not to be pulled in. At the same time we are not traveling so fast that we fly out of the sun's gravitational reach. We are in orbit, the perfect balance between gravity and speed.

Earth travels at 67,000 miles per hour (107,870 km per hour) around the sun. Scientists have learned that the space shuttle leaving Earth has to travel at approximately 25,000 miles per hour (40,250 km per hour), and travel at approximately 17,250 miles per hour (27,775 km per hour) to stay in an orbit 200 miles (325 km) high before falling back to the ground. The speed at which satellites have to travel to maintain orbit is dependent upon the height of the orbit. This is the formula for the velocity needed to keep objects in orbit around Earth:

V = 1,113,263/v3,963 + A.
where:
V = velocity in miles/hour
A = height in miles.

On Earth's surface, we can escape gravity. We will attempt to simulate this balance of speed and gravity in this activity using a bucket filled with water and a strong arm.

Instructional Procedures:

  1. Go outside and fill a bucket with water.
  2. Ask the students to predict what would happen if we held the bucket right side up over their heads. (The bucket holds the water and they won't get wet.) Ask them what would happen if we turned the bucket up-side down. (They would get wet.) What about if we tipped the bucket on its side? Why would the water fall out of the bucket (gravity)?
  3. Ask the students if there would be anyway to keep the water inside of an upside down bucket? Let the students develop experiments to keep the water inside of the bucket. Most students will pick up on the idea of speed. If not, volunteer to try out your own experiment. Swing the bucket up over your head and back down to the ground. Have the students try the same, or variations of the same, experiment.
  4. Explain that in our solar system we just acted like the sun, while the water in the bucket would be Earth. Our arms acted like the force keeping Earth from moving toward the Sun. If Earth was not moving fast enough it would be pulled directly into the sun, in the same way water would fall out of the bucket if we did not move the bucket fast enough when above our heads.

Discussion:

Why doesn't water fall out of the bucket? Why didn't the bucket just go flying away into outer space? (We weren't quite that fast - spacecraft need to be traveling at least 25,000 miles per hour to get off of Earth.) Why doesn't Earth go flying off into space? (The sun's gravity is still strong enough to keep the Earth's mass in orbit, a place where the force of the sun's gravity and the speed of the Earth balance. The Earth travels at 67,000 miles/hour to stay in balance). Could we keep the bucket swinging over our head forever? Why not? (Our forces would not be quite balanced - we would get tired of putting energy in to the swinging, counteracting Earth's gravitational pull and water would fall out.)

Variation:

If you cannot get outside, try using a bucket full of shredded paper, paper clips, or some other dry material that is safe enough to swing over student's heads.

Included National Parks and other sites:

Canaveral National Seashore

Photos:

Earth
Sun
Space Shuttle

Utah Science Core:

3rd Grade Standard 3 Objective 1,2
3rd Grade Standard 4 Objective 1,2
6th Grade Standard 3 Objective 3

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Did You Know?

Bryce Canyon Paintbrush

The Bryce Canyon Paintbrush was discovered June 24, 1965 at Inspiration Point in Bryce Canyon National Park. This rare wildflower is only found in southwestern Utah. More...