UNIT: CATAPULT

ACT-Based Science: Elasticity & Energy Transfer Experiment

OBJECTIVE:

Students test how elasticity affects projectile motion.

Materials Needed:

Rubber bands of varying thickness

Ruler

Force meter

Student Directions:

Goal:
You will investigate how the elasticity of rubber bands affects the amount of energy stored and transferred during a catapult launch. By measuring applied force and launch results, you’ll explore the relationship between elastic potential energy and projectile motion.

Step 1: Prepare Your Materials

Gather:

3–4 rubber bands of different thicknesses or lengths

A ruler or measuring tape

A force meter (spring scale or equivalent)

Your projectile (marshmallow, ball, or other safe object)

A catapult base or simple launch setup

Label each rubber band A, B, C, etc., for easy tracking.

Step 2: Test Force and Launch Distance

For each rubber band:

Attach the band to your catapult or launcher.

Use the force meter to measure how much force is needed to stretch the rubber band to a fixed length (e.g., 10 cm).

Record this value in newtons (N).

Launch the projectile and measure the distance it travels.

Use the ruler or measuring tape from the launch point to the landing spot.

Repeat 3 times per band and record each result.

Sample Data Table:

Rubber Band	Stretch Distance (cm)	Force Applied (N)	Launch 1 (cm)	Launch 2 (cm)	Launch 3 (cm)	Average Distance (cm)
A	10	2.1	180	175	185	180
B	10	3.5	…	…	…	…

Step 3: Analyze the Results

For each rubber band, calculate the average launch distance.

Compare:

Which rubber band stored and transferred the most energy?

Is there a clear relationship between force applied and distance launched?

Answer the following questions in your notebook or on the worksheet:

Which rubber band produced the farthest launch? Why?

Which required the most force to stretch? What does that suggest?

How does elasticity (how much the band can stretch and snap back) influence energy storage?

Step 4: Discuss & Reflect

With a partner or group, discuss:

"How does elasticity contribute to the storage and transfer of energy during a catapult launch?"

Use science vocabulary in your discussion:

Elastic potential energy

Force

Energy transfer

Projectile motion

Optional Extension:

Try changing the stretch distance (e.g., 5 cm, 10 cm, 15 cm) and observe how that affects launch distance.

Create a line graph of:

X-axis: Force applied (N)

Y-axis: Average launch distance (cm)