Projectile Motion: Horizontal Launch

Active learning works for projectile motion because students often hold intuitive but incorrect ideas about how objects move through the air. By physically launching marbles and carefully observing their paths, students experience the independence of horizontal and vertical motion firsthand, replacing abstract equations with concrete evidence.

• 9th Grade
• Physics
• 3 activities
• 20 min–50 min

Learning Objectives

1. Calculate the horizontal range of a projectile launched horizontally, given its initial speed and height.
2. Predict the time of flight for a horizontally launched projectile based on its vertical displacement.
3. Explain the independence of horizontal and vertical motion for a horizontally launched projectile.
4. Analyze how changes in initial horizontal velocity affect the landing position of a projectile.
5. Compare the trajectory of a horizontally launched projectile with that of a projectile launched at an angle.

Inquiry Circle

⏱ 50 min·Small Groups

Inquiry Circle: Marble Launcher Landing Spot

Groups fire a marble horizontally from a known height using a ramp. They measure the launch height and use slow-motion video to estimate initial horizontal velocity, then calculate the predicted landing distance. Groups mark the predicted spot with tape and fire to test their prediction.

Prepare & details

How does the horizontal velocity of a projectile change throughout its flight?

Facilitation Tip: During Collaborative Investigation: Marble Launcher Landing Spot, circulate and ask each group to justify their predicted landing spot using both the time of flight calculation and the horizontal velocity measurement.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Think-Pair-Share

⏱ 20 min·Pairs

Think-Pair-Share: The Time Link

Pairs work through a two-step problem where they must first use the vertical free-fall equation to find time of flight, then use that time in the horizontal equation to find range. Each pair explains the role of the shared time variable to another pair before the class compares solutions.

Prepare & details

Predict the landing spot of a horizontally launched projectile given its initial conditions.

Facilitation Tip: During Think-Pair-Share: The Time Link, listen for pairs who recognize that the ball dropped straight down and the horizontally launched ball hit the ground at the same time, then invite them to share that observation with the class.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Gallery Walk

⏱ 30 min·Small Groups

Gallery Walk: Trajectory Diagram Annotation

Posted diagrams show horizontally launched projectiles at different heights and speeds. Groups annotate each diagram with horizontal velocity vectors, vertical velocity vectors at multiple time intervals, and the net velocity direction at each point, then rotate to compare annotations with the previous group.

Prepare & details

Explain why the time of flight for a horizontally launched projectile depends only on its vertical drop.

Facilitation Tip: During Gallery Walk: Trajectory Diagram Annotation, provide a checklist of elements to include (initial velocities, acceleration vector, time intervals) so students know exactly what to look for as they move between stations.

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Teaching This Topic

Teach this topic by starting with a dramatic demonstration: drop a ball and launch another horizontally from the same height at the same moment. The audible ‘thud’ of both hitting the ground together immediately challenges the misconception that horizontal speed affects flight time. Avoid rushing to equations before students see the phenomenon. Research suggests students learn best when they first observe, then measure, and finally model the motion with graphs and calculations.

What to Expect

Successful learning looks like students explaining why horizontal velocity doesn’t affect time of flight, accurately predicting landing spots using calculations, and annotating trajectory diagrams with clear labels for velocity components and acceleration arrows. They should connect mathematical predictions to physical outcomes during hands-on experiments.

Watch Out for These Misconceptions

Common Misconception

During Collaborative Investigation: Marble Launcher Landing Spot, watch for students who argue that a faster marble will fly longer because it travels farther.

What to Teach Instead

Use the marble launcher setup to show that marbles launched from the same height, regardless of horizontal speed, hit the ground at the same time. Have students measure the time of flight for different speeds using a stopwatch or motion sensor.

Common Misconception

During Gallery Walk: Trajectory Diagram Annotation, watch for students who draw curved or decreasing horizontal velocity vectors.

What to Teach Instead

Have students compare their diagrams to the marble’s actual path captured on video or a slow-motion animation. Ask them to redraw the horizontal velocity vectors as straight, equally spaced arrows to match the constant speed.

Assessment Ideas

Quick Check

After Collaborative Investigation: Marble Launcher Landing Spot, provide students with a diagram of a ball rolling off a table at 4 m/s from a height of 0.8 m. Ask them to write the initial horizontal velocity (4 m/s) and initial vertical velocity (0 m/s), then identify that only the vertical component is affected by gravity.

Exit Ticket

After Think-Pair-Share: The Time Link, present students with a scenario: 'A ball is launched horizontally from 2 meters with a speed of 6 m/s. Calculate time of flight and horizontal range.' Students submit their answers and show their calculations for both components.

Discussion Prompt

After Gallery Walk: Trajectory Diagram Annotation, pose the question: 'If you triple the horizontal launch speed of a projectile, how does its time of flight change? How does its range change?' Ask students to explain their reasoning using their annotated diagrams as evidence.

Extensions & Scaffolding

• Challenge: Ask students to calculate the minimum horizontal speed needed for a marble to clear a gap between two tabletops spaced 30 cm apart, launched from 1 meter high.
• Scaffolding: Provide a partially completed trajectory diagram with some velocity vectors and acceleration arrows already drawn for students who struggle to begin.
• Deeper: Have students research how air resistance would alter the motion, then design and conduct an experiment to measure its effect using a fan and varying launch speeds.

Key Vocabulary

Projectile Motion	The motion of an object thrown or projected into the air, subject only to the acceleration of gravity and air resistance (though often simplified to only gravity).
Horizontal Launch	The initial velocity of a projectile is entirely in the horizontal direction, with no initial vertical component.
Time of Flight	The total duration that a projectile remains in the air from the moment it is launched until it hits the ground.
Range	The total horizontal distance traveled by a projectile before it lands.
Independent Motion	The concept that the horizontal and vertical components of a projectile's motion can be analyzed separately, as they do not affect each other.