UNIT: CATAPULT

ACT-Based Writing: Writing a Technical Explanation of a Catapult’s Mechanics

OBJECTIVE:

Student’s practice writing clear and structured explanations of the physics behind catapult motion.

Materials Needed:

Notes on projectile motion

Newton’s laws

Energy transfer; example technical articles; writing rubric

Student Directions:

Goals:
You will write a clear and accurate technical explanation of how a catapult works, using scientific vocabulary and evidence. This activity strengthens your ability to explain complex systems using precise and logical writing—just like what is required on the ACT and in engineering careers.

Step 1: Plan Your Writing

Before writing, review your class notes and materials:

Projectile motion (trajectory, range, launch angle)

Forces and Newton’s Laws (First, Second, and Third Laws)

Energy concepts (potential energy, kinetic energy, energy transfer)

Look at example technical texts to see how professionals explain similar systems.

Then, outline your explanation using a logical sequence:

What parts make up a basic catapult?

What happens when you pull back the arm?

What forces and energy changes occur during the launch?

What factors influence how far the projectile goes?

Step 2: Write Your Technical Explanation

Write a well-organized explanation using paragraphs or numbered steps. Be sure to:

Use precise scientific terms (e.g., tension, force, gravitational pull, trajectory, velocity).

Include definitions of important terms.

Explain each stage of the catapult's motion from setup to launch.

Use cause-and-effect language (e.g., “Because the rubber band is stretched…” or “As the arm is released…”).

Refer to real data or examples if available (e.g., “In our test, a 45° launch angle produced the longest range”).

Step 3: Address the Prompt

Use the following writing prompt as your central focus:

Essay Prompt:
Explain the relationship between launch angle and projectile distance in a catapult. Use scientific evidence to support your explanation.

In this section of your explanation:

Describe how different angles affect the height and distance of a projectile.

Explain why 45° is typically the most efficient angle for maximum distance.

Include evidence from physics principles or your own classroom data.

Step 4: Review and Revise

Use a rubric or editing checklist to check for:

Clarity and logical flow

Use of accurate scientific terms

Correct spelling, grammar, and sentence structure

Ask a peer to read your explanation and give feedback:

Could they understand each step clearly?

Did your writing sound technical and precise?

Step 5: Class Discussion

Join a small group or class discussion and reflect on these questions:

How do engineering principles (like tension and leverage) affect how efficiently a catapult launches a projectile?

Why is clarity in technical writing important for engineers and scientists?

Essay Prompt: Explain the relationship between launch angle and projectile distance in a catapult. Use scientific evidence to support your explanation.

ACT-STYLE QUESTION:

Which of the following revisions best improves clarity in a technical explanation of catapult motion?

"A catapult moves when you release the arm, sending stuff flying far."

"Upon release, stored potential energy in the catapult arm converts into kinetic energy, propelling the projectile forward."

"If you let go, the object will go forward because of energy."

"The arm goes down and then up, launching the object using physics."