Teacher Guide

# Watch it Fly

## Experimenting with forces and variables of flying objects

How does the mass of a projectile and its initial velocity affect how far it flies and how fast it drops?

This resource was originally published in PhysicsQuest 2020: Force & Motion.

This is the teacher guide for this lesson. A student-focused guide to assist learners as they perform the activity is available.

View the student guide: Watch it Fly

How does the mass of a projectile and its initial velocity affect how far it flies and how fast it drops?

• 4 Rubber bands
• 2 sets of chopsticks
• 4 different-sized wooden balls
• A roll of masking tape

This activity is designed for students to practice designing an experiment. An example set up is provided if students would like to use that example to get started. While they experiment students will keep track of variables and collect data. At the end, students will discuss what they believe to be true based on their data.

### Safety

• Make sure that students are out of the way before launching the wooden balls off of the table.
• Make sure you have plenty of space in front of your slingshots, your projectiles can fly very far.
• Total time
45 - 60 minutes
• Education level
• Content Area
Force and Motion
• Educational topic
Gravity, mass, arc

The Science Behind Flying Objects: When something is moving, it is going to continue moving in the same way unless acted on by a force. This is Newton’s first law of motion. If a hockey puck is moving on the ice, it is going to continue moving in the same direction unless it is hit by something like a hockey stick. As the puck scoots across the ice, the force of gravity is pulling it down. If we assume the ice is perfectly smooth and there is no friction, then we can assume that there is no force acting in the direction the puck is moving. So it will happily stay moving in that same direction until a force does come along, maybe a hockey player trying to shoot a goal. Just because something is moving, doesn’t mean there is currently a force acting on it, and just because something is motionless doesn’t mean there are no forces acting. All of this is true in projectile motion as well. When something is launched off the edge of a counter or table, it has been given some initial velocity (in this experiment, by a slingshot) and then begins to fall down toward the ground. But as soon as the object leaves the table, the only forces that are acting on it are the force of gravity and the force of air resistance. There are no forces acting in the horizontal direction to change its forward motion, just its motion toward the ground. Because of this, as the ball flies through the air and eventually hits the ground, it will always be moving forward with the same velocity.

But will this forward velocity change how it falls toward Earth? No, not at all. Motion in one direction does not affect motion in another. So how fast an object falls depends only on how hard the Earth is pulling, not on how fast the ball is moving forward. In this experiment, students will see that no matter how the initial velocity or how the mass of the moving object changes, the balls will always take the same time to fall.

Key terms

These are the key terms that students should know by the END of the two lessons. They do not need to be front loaded. In fact, studies show that presenting key terms to students before the lesson may not be as effective as having students observe and witness the phenomenon the key terms illustrate beforehand and learn the formalized words afterwards. For this reason, we recommend allowing students to grapple with the experiments without knowing these words and then exposing them to the formalized definitions afterwards in the context of what they learned.

However, if these words are helpful for students on an IEP, ELL students, or anyone else that may need more support, please use at your discretion.

• Mass: A measure of the amount of stuff (or matter) an object has. Not to be confused with weight or volume. Mass only says how much actual stuff there is, not how big an object is or how hard something is pulling on it.
• Force: The push or pull an object feels because of interactions with other objects. If the interaction stops, then there is no force. It is formally defined as mass times acceleration. For example, gravity is a force that represents the pull the Earth has on all objects.
• Velocity: A measure of how fast something is going in some specific direction. Not to be confused with speed, which is only how fast something is moving. “The car was going 65 mph south on I-95” is a measure of velocity. “The rollercoaster was moving at 65 mph when Billy got sick” is a measure of speed.
• Projectile: An object projected through space because of a force. A thrown baseball or a ball shot from a cannon l are good examples.
Objective

Students will experiment to understand the shape flying objects make.

It is important to understand that student goals may be different and unique from the lesson goals. We recommend leaving room for students to set their own goals for each activity.

Before the experiment
• Use the Turn & Talk Protocol to discuss:

When you throw a ball or launch something from a slingshot, what path does it take? Draw it.

1. Pair students up
2. Give them a minute to think quietly
3. Give students 2 minutes to discuss their thinking
4. Have students record their answers or share out to the whole group
Setting up
• Tape two chopsticks to the edge of a table 3 inches apart with about 3 inches of chopstick above the table. Do the same with the second set of chopsticks on the same table edge about 6” away from the first set.

• Take two rubber bands and tie them together. Do this again with another two rubber bands.

• On each set of rubber bands, put a piece of masking tape over the knot so that you have a little handle.

• Put the sets of rubber bands on the chopsticks to create a slingshot!

• Put strips of tape 4”, 6.5”, and 9” back from the edge of the table.

• Label the balls 1 through 4 from largest to smallest.

• Place ball 1 at the edge of the table in one of the chopstick sling shots and ball 2 in the other. (Figure 1)

• Pull the rubber bands back to the closest strip of tape and let go, launching the balls. Put a piece of tape where each of the balls hit and label it with the ball number and the distance the rubber band was pulled back. Do this at least three times, marking with tape each time. It’s always important to do repeated trials. Find the average distance traveled. Note which ball hit the ground first.

• Now do the same thing, but pull the rubber band back to the second strip of tape. Again do this 3 times and find the average. Each time, note which ball hit the ground first. Repeat for third tape position.

• Repeat with balls 1 & 3, 1 & 4, 2 & 3, 2 & 4, and 3 & 4. Each time, note which ball hits the ground first. Different groups can try different initial positions of the slingshot and different combinations of masses and then have a group discussion about their findings. Repeat these combinations for each tape position.

• Repeat the experiment with all the balls but instead of using the sling shot just drop the balls from the same height you were shooting the balls in previous steps. Compare the times it takes the balls to hit the ground when they are dropped — just vertical direction — vs when they are slingshot having horizontal and vertical directions. Considered if the recording time you are comparing is from the moment you release the ball from the slingshot or the moment the ball leaves the table (or surface).

During the experiment
Collecting data
• In the student’s guide, we have asked the students to design their own experiment to test if two objects of the same mass and two objects with different masses will hit the ground at the same time, when one is given an initial velocity forward and the other one is dropped from the same height. The idea is to encourage them to be creative, to understand how to design experiments, and to think like scientists and engineers. They are given a set of materials that they can use to do their experiments. This is to prompt them, but they should be allowed to use other materials in their design. They are also given full instructions for one possible design.

Analyzing data
• The goal of this experiment is for students to understand that mass and velocity forward are not factors that affect how objects fall. They need to figure out which variables they should control for, such as dropping the balls at the same time and from the same height, if there is a strong air current that could affect how the balls fall, and consistency of the repeated experiments.

Teacher tip

Suggested STEP UP Everyday Actions to incorporate into activity:

• When pairing students, try to have male/female partners and invite female students to share their ideas first.
• As you put students into groups, consider having female or minority students take the leadership role.
• Take note of female participation. If they seem to be taking direction and following along, elevate their voice by asking them a question about their experiment.
• Consider using white boards so students have time to work through their ideas and brainstorms before saying them out loud.
• As students experiment, roam around the room to listen in on discussion and notice experiment techniques. If needed, stop the class and call over to a certain group that has hit on an important concept.

Consider using the RIP protocol (Research, Instruct, Plan) for lab group visits and conferring.

Consider culturally responsive tools and strategies and/or open ended reflection questions to help push student thinking, evidence tracking, and connections to their lives.

Conclusion
• Use the What can you say about the effect of horizontal motion on vertical motion? How does horizontal motion affect vertical motion?

1. Students form two circles, one inside circle and one outside circle.
2. Each student on the inside is paired with a student on the outside; they face each other.
3. The teacher poses a question to the whole group and pairs discuss their responses with each other.
4. Then the teacher signals students to rotate: Students on the outside circle move one space to the right so they are standing in front of a new person (or sitting, as they are in the video).
5. Now the teacher poses a new question, and the process is repeated.

### Credits

Coordination, Research, Text, and Editorial Review Claudia Frachiolla, Jamie Liu, Leah Poffenberger, James Roche, Laurie Tangren, Rose Villatoro, David Voss

Graphic Design and Production Meghan White

Illustrations Isabel Bishop

Updated in 2023 by Sierra Crandell, M.Ed. partially funded by Eucalyptus Foundation

Extension by Jenna Tempkin with Society of Physics Students (SPS)