Our world is seldom completely level; more often than not objects are moving in more complex ways. In this lesson students expand their understanding of motion by looking for patterns in how a ball moves up and down a slope.
Goals for the lesson
Ask students to think about the following scenario.
Imagine, a car parked on a hill. In your journal create a diagram adding all the forces and their corresponding vectors for this scenario. When you are finished, turn and talk to your neighbor about your ideas.
If you have individual whiteboards, you might want to use those for students to record their ideas then have them hold up the diagrams and share with the class.
Do not correct any misconceptions at this time. Simply engage students in thinking about the focus for this lesson.
Students investigate Gravity: Motion on a Slope (part 3), using the following four scenarios:
Setup: Mark a "starting line" about 3/4 of the way up each ramp with a piece of masking tape. This is better than using a pen since you can move it if you need to.
They need to create two ramps, one steeper than the other. The greater the difference between the ramps, the more they will be able to see a difference in the ball's motion.
Find two wedges—one thin and the other thick (e.g., a regular book and a 3-ring binder book)—to lift the top of the ramp. You may want to tape the end of the ramp to the table so it doesn't slip out of place when you make it more or less steep.
Students begin with predictions in their investigation of the scenarios.
Predict the motion of the ball by drawing a strobe picture.
Make a prediction of how the velocity of the ball will compare across the different situations.
For example, how will the velocity of the ball on the steep ramp compare with the velocity of the ball on the shallow ramp? If you roll the ball up the ramp and it rolls back down, how will its velocity at the bottom of the ramp compare to when it just rolls down?
Act out the situations. Compare what happens to the ball with their predictions.They may have to try a few times before they are able to roll the ball accurately up to the starting point.
In their journals:
For each of the four situations:
After students have explored the various ramp investigations, have them view and create diagrams for the videos. Two of the videos are of balls rolling down the ramp at two different inclinations (Down Shallow Ramp Video, Down Steep Ramp Video) and the other two videos are of the ball rolling up and back down the same two ramps (Up & Down Shallow Ramp Video, Up & Down Steep Ramp Video).
For each video students should:
To get more information about the forces influencing the ball's motion:
1. Up/down motion forces:
2. Slope motion forces:
The Free Body Diagram - Incline Plane video, while aimed more towards high school students, does a nice job explaining how to construct forebode diagrams on a slope.
To summarize the lesson, ask students to explain their ideas by discussing the following questions with their lab mates.