Uphill Battle

SCIENCE CONCEPT:

Sir Isaac Newton found that things speed up (accelerate) quicker if the force pushing is greater. Can a wheel roll uphill? It can if you make its center of gravity fall as the wheel rises. The center of gravity pushes the wheel uphill. The earth's gravity pulls down on every single particle with a force equal to the weight of that particle. In a body, the forces seem to be concentrated at the 'center of gravity'. Once the center of gravity is hanging outside the base of the object, it will fall over.

STUDENT OBJECTIVE:

The student will explore the center of gravity and how it affects a wheel going uphill.

OVERVIEW:

In this activity, the student will make a wheel that can roll uphill because the center of gravity falls as the wheel rises. The student will use a round lid with rubber bands around the outside of the lid. Then the student will put three marbles inside the lid, secured with modeling clay and roll it up a piece of cardboard.

PREPARATION TIME:

15 minutes.

LESSON TIME:

20 minutes.

TEACHER PREP:

Gather materials for the experiment. You will need marbles, round lid, piece of cardboard, rubber bands, and modeling clay.

WORDS TO KNOW:

center of gravity

matter

mass

inertia

action

reaction

TEACHER TEXT:

All of us experience the force of gravity. It is a force that acts between an object and the earth. It makes things fall by pulling them down. Gravity also keeps everything resting on the ground or on the floor. Gravity still acts on everything, even though the ground or floor prevents movement. It gives everything weight.

When you jump up into the air, why do you fall back down again? You fall because of an invisible force called gravity. Gravity pulls objects toward one another. The strength of this pull depends on the amount of matter an object has - its 'mass'. The larger the object's mass, the greater the pull. The earth is very massive, and its gravity is very strong. It pulls everything on it toward its center, from the smallest animal to the tallest skyscraper.

Forces always act between two objects. One object must push or pull on another. Forces also come in pairs that act on both objects in opposite directions. Isaac Newton, the British scientist, was able to describe how the force of gravity makes objects fall. He was led to this discovery by seeing an apple fall from a tree, and wondered whether gravity might also extend into space. He showed that gravity keeps the planets into their oval paths around the sun. Newton described three laws of motion also. The laws show that force does not sustain motion but only changes it, shows how inertia (a resistance to any change in movement that is possessed by everything) affects motion, and shows that action and reaction exist.

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Last modified: Tue Mar 24 16:24:42 PST 1998