## Projectile Motion

### Carol Houck

#### Description

Students observe projectile motion and calculate the speed of a projectile.

#### Objectives

The student adds, subtracts, multiplies, and divides whole numbers, decimals, and fractions, including mixed numbers, to solve real-world problems, using appropriate methods of computing, such as mental mathematics, paper and pencil, and calculator.

The student knows that the motion of an object can be described by its position, direction of motion, and speed.

The student knows that accurate record keeping, openness, and replication are essential to maintaining an investigator's credibility with other scientists and society.

The student recognizes the scientific contributions that are made by individuals of diverse backgrounds, interests, talents, and motivations.

The student recognizes that patterns exist within and across systems.

#### Materials

Per group:
-Baseball or softball
-Stopwatch
-Ruler
-Paper and pencils
-Baseball field (optional)
-Videodisc-- Physics of Sports (optional)
-Copies of attached file

#### Preparations

1. Discuss projectile motion prior to this activity.

2. Discuss Newton's Laws prior to this activity.

3. Organize materials in advance.

4. Discuss the need for safety when throwing objects.

#### Procedures

Knowledge/Skills:
-Students will observe and understand projectile motion.
-Students will relate speed to direction of motion and time and distance.
-Students will calculate the speed of a projectile based on time and distance traveled.
-Students will utilize data and record keeping skills.
-Students will utilize reading and writing skills.

Background:
-Baseballs follow the laws of physics. This activity introduces some of the forces affecting a pitched ball. Of these forces, the force of the pitcher and the force of gravity are most observable. The force of the pitcher moves the ball forward as gravity pulls the ball down to the ground.
-A successful pitcher uses forces to manipulate each pitch. The batter has to understand the motion of the ball as it comes toward him.
-Data collected will be limited by the ability of the human eye to see an object in motion as well as by the speed at which the button on the stopwatch can be depressed. Data may not be precise, but it should show a pattern of motion.

Procedure:
1. Divide students into groups of three. Assign the following tasks and move outside.
a. One class member is the pitcher.
b. One student is the timekeeper.
c. One student will observe the ball and measure the distance it travels.

Part One: Outside
2. In each group, the pitcher throws as many balls as time allows in a 10 minute period. Some balls should be pitched fast and some should be pitched slowly.

3. In each group, the timekeeper records the time from when the ball leaves the pitcher's hand until it hits the ground. This information is recorded in the data table. See the attached file for a sample data table.

4. In each group, the observer notes where the ball hit the ground and measures the distance in meters from that spot to the pitcher’s hand. This distance is recorded in the data table. The observer is also responsible for drawing the path of the ball's travel in the labeled box of the data table.

5. At the end of 10 minutes, ask students to collect their materials and return to the classroom for data analysis and calculations.

Part Two: Inside
6. Each group calculates the speed of each ball using the formula
Speed = distance ÷ time
The unit of speed should be meters per second.

7. The following questions are answered at the conclusion of the activity.
a. What is a projectile?
b. What is the typical path of all projectiles ?
c. What makes a projectile travel forward?
d. What makes a projectile travel downward?
e. What is speed?
f. What are the units of speed?
g. Based on your activity, which ball traveled farthest?
h. What is the relationship between speed and distance?
i. How can you explain why balls traveled at different speeds?
j. How do Newton's Laws apply to the projectile?
k. As a group, list three inferences that can be drawn from the information in your data table. State these in full sentences.

8. Assess student understanding.

#### Assessments

The following questions may be used to assess student understanding:

1. What force is responsible for pulling a projectile down?
a. friction
b. magnetism
c. gravity
d. wind resistance

(answer c: The ball is pulled downward by gravity.)

2. How is the speed of a projectile determined?
a. Speed is divided by the time.
b. Distance is divided by the time.
c. Time is divided by the distance.
d. Motion is divided by the speed.

(answer b: Speed is distance divided by time.)

3. Which of the following would have the greatest speed?
a. A ball which travels a short distance in a long time.
b. A ball which travels a long distance in a long time.
c. A ball which travels a long distance in a short time.
d. All of these balls will travel at the same speed.

(answer c: Speed is distance divided by time; therefore, a ball traveling a large distance in a short time will have a high speed.)

The following checklist may be used to aid in assessing student laboratory progress:
• Did the group turn in a completed data table that included a title?
• Did the group work cooperatively?
• Were all mathematical calculations done correctly?
• Did the group answer the questions correctly?
• Were the three inferences based on logic?
• Did the group turn in the completed assignment on time?

For sample FCAT questions and solutions, see the attached file.

Self-Reflection:
Devise another experiment that would allow you to measure the time, speed, and distance an object travels more accurately.

#### Extensions

Enhancement:
1. Students can investigate techniques that allow a pitcher to throw a curve ball, a change of pace ball, a fast ball or even a slow ball. What is the physics involved in each case?

2. A baseball is not a smooth sphere; it has stitching. Why is the placement of stitching so critical in determining the path of the ball? Why does a pitcher call for a new ball when the one in use becomes marred in some way?

3. How does the Bernoulli effect influence the path of a thrown baseball?

4. How do pitchers position their fingers for each kind of pitch? How does this affect the pitch?

#### Attached Files

A Sample Data Table and a Sample FCAT Question.     File Extension: pdf