Kinetic & Potential Energy Interconversion on Curved Track

As a marble rolls down a curved track, its height decreases while its speed increases, converting gravitational potential energy into kinetic energy. When it climbs up, kinetic energy turns back into potential energy, keeping the total mechanical energy nearly constant.

Medium ⏱ 45 min ⚗️ Class 9-12 🏠 6 of 7 things are at home

Time: 45 min
Difficulty: Medium
Best for: Class 9-12
Subject: Physics
Things needed: 7, 6 at home
Steps: 12
Cost: Low, a few things to find
You will learn: Conservation of Mechanical Energy

Kinetic & Potential Energy Interconversion on Curved Track, Experiment · Class 9-10 | jijnas.com

Before you start

What you need

0 of 7 ready

Tap each thing once you have it in front of you. Items with the house sign are already somewhere in your home.

Sliced flexible PVC conduit pipe (1.5 meters) or toy track 1 piece No luck? Use sliced foam pipe insulation, split garden hose, or plastic curtain track.
🏠 Glass marble (kancha) or steel ball bearing 2-3 pieces No luck? Use small plastic toy car or metal nut.
🏠 Measuring tape or 1-meter steel scale 1 unit No luck? Use standard 30 cm plastic school ruler.
🏠 Smartphone with slow-motion video or stopwatch app 1 unit No luck? Use digital stopwatch or school lab photogate timer.
🏠 Kitchen digital scale or lab balance 1 unit No luck? Use school physics lab physical balance.
🏠 Cello tape or masking tape 1 roll No luck? Use insulation tape.
🏠 Stack of heavy textbooks or wooden blocks 5-6 books No luck? Use lab retort stands with clamps.

💬 Send to a parent

Think first

What do you think will happen?

Real scientists guess before they look. Write one line now. After the steps, the page will show it next to what you should see.

Do it

The procedure

Tap a step when it is done. Lab mode shows one step at a time in big letters, reads it aloud if you want, and keeps the timer.

Weigh the marble on the digital balance and convert the reading to kilograms.
Anchor the flexible conduit pipe to a stack of textbooks using masking tape to form a curved track with a hill.
Measure the vertical height from the table surface to the starting release point using a measuring tape.
Position a smartphone camera on a tripod to record slow-motion footage of the track.
Place the marble at the top starting mark of the track.
Release the marble from rest without pushing it forward.
Measure the vertical height from the table to several key points along the track, such as hill crests and troughs.
Determine the marble speed at each key point using frame analysis from your video recording.
Calculate the potential energy at each designated height using the formula PE = mgh.
Calculate the kinetic energy at each designated point using the formula KE = 1/2 mv^2.
Add potential energy and kinetic energy at each point to calculate total mechanical energy.
Repeat the release process three times to ensure your measurements are consistent.

01 · The idea

The Concept

Mechanical energy changes form whenever an object rolls down slopes or climbs hills. By setting up a curved track and calculating energy values at different points, you can directly verify how energy stays balanced across a continuous path.

02 · What you should see

Observation

When you release a marble from the top of a curved track, you will observe the following key patterns during its motion:

At the Highest Point: The marble starts from rest with maximum height. Here, its speed is zero, meaning its kinetic energy is zero, while its gravitational potential energy is at its maximum value.
At the Lowest Valley: As the marble rolls down, it gains speed rapidly, reaching its maximum velocity at the lowest point of the track. At this bottom position, potential energy is at its minimum, while kinetic energy reaches its peak.
Climbing the Next Hill: As the marble moves upward, it noticeably slows down, converting its speed back into height. It reaches a height slightly lower than its starting point due to friction.
Calculated Energy Values: When you calculate potential energy (PE = mgh) and kinetic energy (KE = 12mv²) using measured heights and photogate speeds, the sum of both values (PE + KE) remains nearly identical at every point along the track.

03 · Why it happens

Why It Happens

Energy cannot simply vanish or appear out of nowhere; it can only transform from one form to another. On a track, the total mechanical energy is split between stored energy due to height (potential energy) and energy of motion (kinetic energy).

Think of total mechanical energy like having a fixed sum of money split between two pockets. Gravitational potential energy is like cash in your left pocket, and kinetic energy is cash in your right pocket. As the marble rolls downhill, you are taking money out of your left pocket (losing height) and putting it into your right pocket (gaining speed). When the marble rolls uphill, the transfer reverses. The total amount of money across both pockets stays the same throughout the journey, except for a tiny transaction fee lost to friction.

04 · The science

The Science Behind It

This experiment directly demonstrates the Law of Conservation of Mechanical Energy, a central concept in the NCERT Class 9 physics curriculum (Chapter: Work and Energy).

Mechanical energy (E) is the total energy possessed by a system due to its position and motion, defined as:

$E = PE + KE = mgh + 12mv²$

Gravitational Potential Energy (PE = mgh): Depends on the object's mass (m), gravitational acceleration (g = 9.8 m/s²), and vertical height (h) above a chosen reference plane.
Kinetic Energy (KE = 12mv²): Depends on the mass (m) and the square of its speed (v).

In an ideal isolated system free of non-conservative forces, the loss in potential energy during descent equals the exact gain in kinetic energy (Δ PE = -Δ KE). Thus, mgh₁ + 12mv₁² = mgh₂ + 12mv₂². In real-world setups, a small fraction of mechanical energy is dissipated into thermal and acoustic energy due to friction and air resistance, causing the marble to reach a slightly lower height on subsequent peaks.

05 · Take it further

Make It a Project

To turn this experiment into a science fair display, track how changing variables alters energy distribution:

Independent variable: Release height (h) and position along the track markers.
Dependent variable: Speed (v), calculated Kinetic Energy (KE), and calculated Potential Energy (PE).
Control variables: Mass of the marble, track material, and launch conditions.

Display your data using a energy bar chart showing PE and KE at key positions (top, bottom, and second peak). Prepare a graph plotting height against speed to show how total energy remains nearly flat despite individual energy changes.

06 · Questions students ask

FAQs

Why does the marble never reach its original height on the second hill?

Friction between the marble and track, along with air resistance, converts a small portion of mechanical energy into heat and sound. Because total mechanical energy decreases slightly due to these non-conservative forces, the marble loses a bit of peak height on every bounce or hill.

Does a heavier marble roll faster down the curved track?

In an ideal system without friction, mass cancels out in the energy conservation equation, so all objects fall or roll at the same rate. However, a heavier marble has more momentum, helping it overcome track friction better than a light marble.

Where on the track is kinetic energy at its absolute maximum?

Kinetic energy reaches its maximum at the lowest point of the track, often called the valley. At this point, height is zero relative to the reference plane, meaning all initial gravitational potential energy has transformed into maximum speed.

How do you calculate potential energy if the track isn't on the floor?

Measure the vertical height from your chosen reference level, such as the table surface, to the marble. Multiply the marble's mass in kilograms by gravitational acceleration (9.8 m/s²) and the vertical height in meters to find potential energy in Joules.

Why do we use a curved track instead of a straight ramp?

A curved track lets you observe continuous interconversion between kinetic and potential energy as the marble moves through peaks and valleys. It clearly demonstrates both speeding up during descent and slowing down during ascent on a single continuous path.

Write it up

Your lab notebook

Two minutes here and your lab record is done. Everything stays on this device until you copy it out.

Did it work?

What I actually saw What I would change next time

💼 Same science, as a real job

The physics or chemistry on this bench is what a working business charges for. See the numbers, the licences and the worst case before anyone spends a rupee.