# Investigating gravity: Predicting time to hit the ground, and finding that dropped and horizontally shot objects hit the ground at the same time.

#### Summary

In this physics lab, students drop and shoot horizontally "Nerf" balls from a variety of known heights. Students use lab notebooks to record the amount of time it takes for the ball to hit the ground for each trial. Students plot height vs. time data in Excel, and they create a trend line for the dropped and shot balls. Students will use the trendline to predict as accurately as possible (with error bars) how long it will take a ball to hit the ground from a certain distance. Students will also discover that launched and dropped balls take the same amount of time to hit the ground when started from the same height.

## Learning Goals

## Context for Use

Time needed for activity and data interpretation: about 2 hours.

Special Equipment needed: "Nerf-type guns" that shoot out foam balls, measuring tape, timers, gym bleachers.

Previously-learned Skills necessary: none (except a very basic understanding of Excel); this can be used to introduce a gravity unit or it can be used at any point in the unit.

This activity can be easily adapted to other settings—the main requirement is accessible high points from which to drop the balls from.

**Subject**: Physics:Classical Mechanics:Gravity

**Resource Type**: Activities:Field Activity, Lab Activity

**Special Interest**: Field-Based Teaching and Learning

**Grade Level**: High School (9-12)

**Theme**: Teach the Earth:Enhancing your Teaching:Teaching in the Field

## Description and Teaching Materials

At the end of the data-collecting phase, the group will have 5 height vs. time data points for dropped balls, and 5 height vs. time data points for shot balls.

Groups will be allowed time in a computer lab for data analysis. Groups should create two graphs, one a height vs. time graph for dropped balls, and one a height vs. time graph for shot balls. Each group should then create a line of best fit with an equation for each of the graphs. Each group is given a height, and they must use their equations to determine as accurately as possible, with error bars, how long it will take a dropped ball and a shot ball to hit the ground from the given height.

This lesson is concluded the next day of class, when the teacher drops and shoots a ball from the given height. Students will be able to see how close their predictions were. A discussion can follow about the lab and the forces involved with the dropped balls and the shot balls.