UNIT: CATAPULT

ACT-Based Science: Newton’s Laws & Catapult Motion

OBJECTIVE:

Students observe and apply Newton’s Laws to catapult mechanics.

Materials Needed:

Catapult

Stopwatch

Weights

Notebook

Student Directions:

Goal:
You will explore how Newton’s First, Second, and Third Laws of Motion apply to the mechanics of a catapult. By launching different weighted projectiles, you’ll observe how mass and force affect motion and acceleration.

Step 1: Prepare Materials

Gather the following:

A working catapult

At least 3 projectiles of different masses (e.g., ping pong ball, rubber ball, metal washer)

Stopwatch

Ruler or measuring tape

Notebook or data sheet

Scale (if available, to weigh each projectile)

Step 2: Conduct Launch Trials

Weigh each projectile and record its mass in grams (g) or kilograms (kg).

Keep the catapult tension or pullback distance constant for all trials.

For each projectile:

Load it into the catapult.

Launch it and measure how far it travels.

Use the stopwatch to measure how long it is in the air (time of flight).

Record observations about speed, distance, and height.

Sample Data Table:

Projectile	Mass (kg)	Distance (m)	Time of Flight (s)	Notes on Motion
A (light)	0.02	5.2	1.3	Fast, high arc
B (medium)	0.05	3.8	1.1	Slower, lower
C (heavy)	0.10	2.4	0.9	Short, low arc

Step 3: Apply Newton’s Laws

As you observe and record, connect what you see to Newton’s Laws:

Newton’s First Law (Inertia):

How does mass affect how easily a projectile starts or stops moving?

Which projectile resisted motion the most?

Newton’s Second Law (F = ma):

How does increasing the mass affect the acceleration when the force from the catapult remains constant?

Use the data to explain how more mass = less acceleration.

Newton’s Third Law (Action–Reaction):

When the catapult arm pushes on the projectile, what is the equal and opposite reaction?

What evidence do you see of this reaction?

Write a short explanation in your notebook for how each law applies to your catapult launches.

Step 4: Group Discussion

With a partner or your group, discuss:

“How does increasing mass or force impact acceleration and motion?”
“How do Newton’s Laws help engineers build better catapults?”

Use vocabulary like:

Inertia

Force

Acceleration

Action–Reaction

Mass

Motion

Extension (Optional):

Try launching the same projectile with different pullback distances to change the force applied.

Compare how increasing force affects acceleration and travel distance.