Egg-Citing Eggs-Periments

Who knew the humble egg could be a science superstar? But our kitchens hold a fantastic, fragile, and fascinating tool for exploring some core physics concepts. So, forget boring textbooks and see some physics in action – with the following egg-citing eggs-periments!

1. The Spinning Egg Challenge: The Law of Inertia
2. Soft Landing of an Egg: Force, Impulse, Momentum
3. Hard Landing of an Egg: Energy Transformation
4. The Floating Egg: Density and Buoyancy

1. The Spinning Egg Challenge: The Law of Inertia

The core idea behind Newton’s First Law is this: an object will either remain at rest or keep moving in a straight line at a constant speed unless an outside force makes it change its state of rest or motion. Let’s see this in action with eggs.

Cracking Open Newton’s Law of Inertia

Here’s a classic experiment that can be used as a challenge in a classroom where students are asked to identify a raw egg from a hard-boiled one without cracking it open.

Class Discussion

This challenge can lead to a class discussion in which students might guess various ways of identifying which egg is raw/boiled and their guesses / hypotheses could be experimentally tested.

Conducting The Experiment

1. Place the boiled and the raw egg on a flat plate.
2. Give each egg a good spin.
3. After they’ve been spinning for a couple of seconds, gently touch each egg with your finger to stop its rotation for a moment, then quickly release it.

REFERENCE VIDEO: https://www.youtube.com/watch?v=Avj7Z0CXIFE

Observations

You’ll notice that one egg stops immediately when you touch it, while the other seems to want to keep spinning, wobbling a bit, and then resuming its spin.

The Physics Behind It (Inertia!)

The hard-boiled egg stops instantly because it’s a solid mass. When you stop the shell, the entire egg stops.

The raw egg, however, has a liquid yolk inside. When you stop the shell of the raw egg, the liquid inside wants to keep moving due to inertia (i.e. an object’s tendency to resist changes in its state of motion or rest). This continued motion of the liquid causes the egg to wobble and often resume spinning even after you’ve briefly touched it.

Inertia in Everyday Life

You experience inertia all the time:

• When a bicycle suddenly stops, the rider tends to continue moving forward.
• When a car suddenly brakes, the driver continues to move forward – that’s why seatbelts are crucial.

2. Soft Landing with an Egg: Understanding Impulse and Momentum

Have you ever wondered why dropping something fragile on a hard floor causes it to shatter, but dropping it on a soft cushion leaves it intact? It all comes down to two key concepts of physics: impulse and momentum. We can demonstrate this perfectly with a simple boiled egg.

Conducting The Experiment: Hard Surface vs. Soft Surface

Take a boiled egg and drop it from the same height onto two different surfaces:

1. A hard, unyielding surface (like a concrete floor or a kitchen counter).
2. A soft, yielding surface (like a cushion or a pillow).

The egg dropped on the hard surface will almost certainly crack or break. The egg dropped on the cushion, however, will likely remain perfectly intact.

The Physics Explained: Impulse and Momentum

Let’s break this down using the language of physics:

• Momentum (p): When the egg falls, it gains momentum. Just before it hits either surface, it has the same momentum because it’s falling from the same height and has the same mass and terminal velocity. When the egg comes to a stop, its momentum changes from its initial value to zero.
• This change in momentum (Δp) is the same in both cases, whether it hits the hard surface or the cushion. We can write this as Δp=m.v−m.0, where m is the mass, v is the velocity just before impact and 0, the velocity just after impact
• Impulse (J): Impulse is defined as the change in momentum (Δp). It’s also defined as the force (F) applied over a period of time (Δt). So, we have the relationship:

J=F⋅Δt=Δp

Since the change in momentum (Δp) is the same for the egg in both drops, the impulse (J) is also the same for both scenarios. This means:

F1⋅Δt1=F2⋅Δt2

Where:

• F1 is the force on the egg from the hard surface, and Δt1 is the very short time of impact.
• F2 is the force on the egg from the cushion, and Δt2 is the longer time of impact.

The Verdict: Why the Cushion Saves the Egg

When the egg hits the hard surface, the impact time (Δt1) is extremely short. Since the impulse (J) must remain constant, the force (F1) exerted on the egg must be very large. A large force over a short time causes the shell to crack.

However, when the egg hits the cushion, the cushion deforms, increasing the time of impact (Δt2). Because Δt2 is greater than Δt1, the force (F2) exerted on the egg by the cushion is significantly smaller (i.e., F1>F2). This spread-out force over a longer time prevents the egg from breaking.

In essence, the cushion acts as a shock absorber, increasing the collision time and thereby reducing the damaging force on the egg. This simple egg experiment beautifully illustrates the powerful relationship between force, time, impulse, and momentum.

3. Hard Landing of an Egg: Energy Transformation

The simple act of dropping an egg can beautifully illustrate fundamental physics concepts – how potential energy transforms into kinetic energy, and the work done by gravity. Let’s follow an egg’s journey from height to its final impact.

Imagine an egg at three different points during its drop – 1, 2, and 3:

Point 3: Just Before Impact (Lowest Point)

• Kinetic Energy (KE): The egg has reached its maximum speed just before hitting the surface, so its kinetic energy is at its maximum.
• Potential Energy (PE): The egg is at its lowest height, meaning its potential energy is at its minimum (or effectively zero if we define the ground as zero potential energy).

Note: The Total Energy (TE) = PE + KE remains constant

After the Egg Reaches the Ground & Stops, Where Does its Kinetic Energy Go?

When the egg finally hits the surface and cracks, its kinetic energy, which was at its peak just before impact, rapidly converts into other forms of energy. This energy is used to:

• do the work required to deform and break the eggshell.
• produce the cracking sound.
• generate a small amount of heat.

Essentially, the force of impact, acting over a very short distance, utilizes that built-up kinetic energy to overcome the structural integrity of the eggshell, causing it to crack.

4. The Floating Egg: Density and Buoyancy

This one needs a just few simple ingredients, and it’s super cool!

The Experiment:

1. Fill two clear glasses with tap water.
2. Gently place an egg in one glass. It will likely sink.
3. In the second glass, add several spoonful of salt and stir until dissolved. Keep adding salt until no more dissolves.
4. Gently place another egg into the salt water.

What to Observe: The egg in the tap water sinks, while the egg in the saltwater floats.

The Physics Behind

This is a perfect demonstration of buoyancy and density. An object floats if it is less dense than the fluid it’s in. Tap water is less dense than an egg, so the egg sinks. When you add salt to the water, you increase the density of water. Eventually, the salt water becomes denser than the egg, providing enough buoyant force to make the egg float. This is the same principle that allows ships to float!

By Nilanjan P Choudhury, STEM Leader, CuriousEd