Science Behind

Why IS liquid nitrogen so cold? What is dry ice made of? Learn about the science behind the fun activities during this year’s Snow Day!

DEMOS

Liquid Nitrogen

Nitrogen is an element that makes up 78% of the earth's atmosphere. Commonly, we encounter nitrogen as a gas, and it takes A LOT of energy to condense it into a liquid! For nitrogen to stay liquid, it must be kept at -321 F (or -196 C). When room temperature objects are exposed to liquid nitrogen, their physical properties may change, becoming more brittle. For example, a rubber ball exposed to liquid nitrogen can shatter...like glass!

  • Gas is less dense than liquid! Lower temperature = smaller volume, and higher temperature = higher volume

  • When liquid nitrogen warms, it expands 700 times, turning back into a gas. When this happens, it should not be contained, or an explosion will occur. A special insulated flask called a Dewar flask is used to keep the liquid nitrogen cold.

FROSTY BUBBLES

When dry ice is added into warm water, the water begins to bubble vigorously and create a fog in the jug. The smoke or fog that is created is caused when dry ice is warmed rapidly. This is called sublimation. Sublimation is when a solid transitions to a gas state without passing through the liquid state. Dry ice is compressed, frozen carbon dioxide gas. Once the dry ice is added to the warm water, it combines with the water to create the smoke or fog. The fog is the mixture of carbon dioxide and water vapor. When added to a soap solution, the smoke filled bubbles are created.

FROSTEE CHALLENGE

Water exists in three states: solid (ice), liquid (water), and gas (water vapor). When a t-shirt is frozen, the water in the fabric changes from a liquid to a solid (ice), making the t-shirt stiff and difficult to wear. The frozen fibers in the t-shirt become rigid and difficult to move or stretch. The frozen water in the t-shirt needs heat to melt and return to liquid form. Touching the t-shirt transfers heat to the fabric, helping it warm up, and, eventually, making it easier to put on.

SNOWBALL SLINGSHOT

The farther you pull back the slingshot, the more tension and potential energy you are creating. When you launch the snowball, that energy is converted into kinetic energy to send the snowball flying to hit the target.

HOT ICE

When things react in science, they can either give off heat or take in heat. This happens in both physical changes (like melting ice) and chemical reactions (like baking a cake). Exothermic reactions are reactions that release heat, making the surroundings warmer. This is called an exothermic reaction because "exo-" means "out," and the heat goes out into the surroundings.

SNOWFAKES

A simple chemical reaction occurs when you mix baking soda and shaving cream, forming a number of new substances – sodium stearate, carbon dioxide and water – that look and feel like snow! The snow feels cold because the chemical reaction causes the liquid in the shaving cream to evaporate. This is a type of chemical reaction known as an endothermic reaction, which means it takes in heat and causes its surroundings to be cooler.

MINI SLED DERBY

Downhill, gravity-assisted racing is about one thing: mass. Mass placement affects the potential energy. To calculate potential energy, the formula PE = mass x gravity x height is used. Typical rules for pinewood derby racing limit the mass of the car up to a certain point. So if you cannot make the mass of the car greater and gravitational pull on Earth is constant, how do you make the car faster?

 

ACTIVITIES

SNOWFAKES

A simple chemical reaction occurs when you mix baking soda and shaving cream, forming a number of new substances – sodium stearate, carbon dioxide and water – that look and feel like snow! The snow feels cold because the chemical reaction causes the liquid in the shaving cream to evaporate. This is a type of chemical reaction known as an endothermic reaction, which means it takes in heat and causes its surroundings to be cooler.

SNOWBALL SLINGSHOT

The farther you pull back the slingshot, the more tension and potential energy you are creating. When you launch the snowball, that energy is converted into kinetic energy to send the snowball flying to hit the target.

MINI SLED DERBY

Downhill, gravity-assisted racing is about one thing: mass. Mass placement affects the potential energy. To calculate potential energy, the formula PE = mass x gravity x height is used. Typical rules for pinewood derby racing limit the mass of the car up to a certain point. So if you cannot make the mass of the car greater and gravitational pull on Earth is constant, how do you make the car faster?

Mass loads that are placed further towards the back of the car tend to raise the center of mass of the car slightly higher, giving a greater amount of potential energy (PE). When the car is released, that energy is converted into kinetic energy (KE). Since the car has the mass slightly higher, there is a bit more PE and it runs out as KE for a longer period.

  • Other variables that affect car speed include: friction (between the wheels and axles, and the wheels and track), aerodynamics, and wheel alignment.

Snowy Spaghetti Tower Challenge

The Engineering Design Process (EDP) focuses on solving a challenge or problem, considering any design limitations, and making changes to improve the product as you go. Building strong towers relies heavily on physics, particularly the forces acting throughout the structure. One of the primary forces to consider is gravity, which pulls objects toward each other and anchors everything on Earth downward. The strength of gravitational pull on an object depends on its mass (the amount of matter it contains); the greater the mass, the stronger the gravitational pull.

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