Steep vs. Shallow

Essential Question
What is the relationship between potential and kinetic energy? How can you measure the speed of an object?

Objectives

 * Show the functional relationship between the height an object falls from and its speed.

Introduction & Student Background
Everyone understands that as an object falls it accelerates, but the way in which it accelerates is less clear. Objects falling under gravity, even on an incline, have constant acceleration, so the speed increases by equal amounts in equal time intervals. This exercise focuses on the concepts of mechanical energy and the conservation of energy.

Vocabulary

 * kinetic energy
 * potential energy
 * conservation of energy
 * fall
 * accelerate

Materials

 * pipe insulation
 * marbles
 * masking tape
 * plastic cup

PREP

 * 1) Cut the insulation in half lengthwise. This forms the 'track' of the roller coaster.

ACTIVITY

 * 1) Shape the insulation to allow the marble to roll from your hand down to a flat section of the track and into a cup.
 * 2) By changing the shape of the track, you can make two tracks side by side, one steep and one shallow. It is important that they both start from the same height and end at the same height. In between the start and finish, they only drop.
 * 3) Which marble will get to the end fastest on which track?

ADDITIONAL ACTIVITY

 * Place the two tracks on a table top with the ends side-by-side at the edge of the table. When the marbles run off, they will travel different horizontal distances determined by their horizontal speed.
 * OR: Place the two tracks on the floor side by side. Make the end of the tube into a small ramp that will launch the marbles up and then let them fall. They fly different distances based on their speeds.
 * Place the two tracks with their ends side-by-side. Add onto the tubes with a gentle upward curve anchored on a meter stick. The marbles will travel a distance up the hill proportional to their speeds.

How it fits to Standard

 * Forces are pushes and pulls. Motion is a change in position.
 * Forces on objects make them move. Changes in forces will cause changes in the motion.

Follow-Up
Both start with the same potential energy, therefore they end with the same kinetic energy. A is first. Both speeds are equal.