Gravitational attraction (Roman Meneses)

Gravity

Title: Why doesn't Earth Fly Off Into Space?

Principle(s) Investigated: Gravity

Standards : CA SCIENCE STANDARDS/ PHYSICAL SCIENCE

• 8.2.g. Students know the role of gravity in forming and maintaining teh shapes of planets, stars, and the solar system
  • 8.2.c, Students know when the forces on an object are balanced, the motion of the object does not change.

Materials: Ball, string, clothes pin, bay leaf, penny, white sheet of paper, ziploc bag, color pencils, white boards, and eraser makers, science reflection sheet, and worksheet.

Procedure:

Introducing Gravity on Falling items/Gravity and the solar system.

• Students will be grouped together and will be given a Ziploc bag with different items inside. (sheet of paper, penny, clothes pin, bay leaf,
• The group will select two different items from the Ziploc bag and write down the name of the two items on their worksheet
• One Students from the group will drop both selecteed items six feet high and see what item reaches the floor first.
• Another student from the group will circle the item that reached the floor first on their worksheet.
• The group will select two additional item and use the same process with different objects till all the items have been dropped.
• The group will write down their results on the worksheet.
• Teacher will then ask students what two items did not reach the floor at the same time? and why?
• Teacher will ask the students what is gravity ? .
• Teacher will then ask studetns: Why doesn't Earth Fly Off into Space? Teacher will explain Newton's first law of motion.
• Teacher will then demonstrate Earth's Orbit around the Sun
• A plastic ball will be attached to a string
• The teacher will tell students, the ball is the planet. My hand is the Sun. teacher will attempt to get the planet to orbit the Sun.
• Teacher willl twirl the ball in a circle over their head for a few Seconds. Then discuss the orbit demonstration
• Teacher will then get ball twirling over the head again, and then announce that you are going to stop pulling on the planet. Release the ball and watch it sail across the room in a straight line.
• Ask students to report the ball;s path of travel after you released the string. They should agree that it flew in a straight line.

Student prior knowledge:

Students would have read Mae Jemison biographical article: The First American astronaunt. The article reinforces the idea that gravity is the force keeping bodies in orbits around other bodies. Students will also watch a video about the solor system: the video will review information they have already learned and provide additional information.

Explanation: All matter has mass. Gravity is a result of mass. therefore, all matter is affected by gravity.

Gravity is a force of attraction between objects that is due to their masses. A heavier object experiences a greater gravitational force than a lighter object does..The flat paper falls more slowly than the heavier objects because of air resistance. Air resistance is the force that opposes the motion of objects through air. The magnitude of air resistance acting on an object depends on the size, shape, and speed of the object

Demonstrate Orbit: While the planet is traveling in its orbit, the pulling on the ball is the pull of gravity. Gravity changes the straightline path of the Earth into a curved orbit. An unbalanced force is needed to change the movement of an object, So, there must be an unbalanced force acting on anything in orbit.This unbalanced force that makes things move in an elliptical path is called a centripetal force. The word centripetal means "toward the center." Gravity provides the centripetal force that keeps things in orbit. The gravitational force between objects depends on the product of the masses of the objects, So, the gravity between objects increases as the masses of the objects increase.

Gravitational Force and Distance: The force of gravity depends on the distance between two objects. As the distance between two objects gets larger,the force of gravity gets much smaller. However , the gravitational force between the sun adn the Earth is larger because they have such large masses. The large gravitational force of the sun affects the movement of all planets.

Stop pulling on the ball/ Newton's Law of Motion: The second part of Newton;s first law is about objects moving with a certain velocity in a straight line.. Such objects will continue to move forever with the same velocity unless an unbalanced force acts on them.

Questions & Answers:

What is gravity? Gravity is the force of attraction between two objects; larger objects, like the Sun, have a greater force of gravity.

Why do planets travel around the Sun in circular paths? Gravity pulls on planets with a force that changes their directions of travel from a straight line into a curved orbit.

Which two forces combine to determine the net force on a fallin object? the force of air resistance is pushing up on the falling object.This force is subtracted from the force of gravity to yeild the net force.

Applications to Everyday Life: Gravity keeps you on Earth and holds the solar system together. Gravity affects the motion of every thing that you drop or throw. Newton's law of motion will help you understand why you and objects around you move in certain ways.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos:

Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.